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We use the NASA GEOS-5 transport model with tagged tracers to investigate the contributions of different regional sources of CO and black carbon (BC) to their concentrations in the Western Arctic (i.e., 50–90° N and 190–320° E) in spring and summer 2008. The model is evaluated by comparing the results with airborne measurements of CO and BC from the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaigns to demonstrate the strengths and limitations of our simulations. We also examine the reliability of tagged CO tracers in characterizing air mass origins using the measured fossil fuel tracer of dichloromethane and the biomass burning tracer of acetonitrile. Our tagged CO simulations suggest that most of the enhanced CO concentrations (above background level from CH4 production) observed during April originate from Asian anthropogenic emissions. Boreal biomass burning emissions and Asian anthropogenic emissions are of similar importance in July domain wise, although the biomass burning CO fraction is much larger in the area of the ARCTAS field experiments. The fraction of CO from Asian anthropogenic emissions is larger in spring than in summer. European sources make up no more than 10% of CO levels in the campaign domain during either period. Comparisons of CO concentrations along the flight tracks with regional averages from GEOS-5 show that the along-track measurements are representative of the concentrations within the large domain of the Western Arctic in April but not in July.

Measurements of ambient OH and HO2 radicals were performed by laser induced fluorescence (LIF) during CAREBeijing2006 (Campaigns of Air Quality Research in Beijing and Surrounding Region 2006) at the suburban site Yufa in the south of Beijing in summer 2006. On most days, local air chemistry was influenced by aged air pollution that was advected by a slow, almost stagnant wind from southern regions. Observed daily concentration maxima were in the range of (4–17) × 106 cm−3 for OH and (2–24) × 108 cm−3 for HO2 (including an estimated interference of 25% from RO2). During daytime, OH reactivities were generally high (10–30 s−1) and mainly contributed by observed VOCs and their calculated oxidation products. The comparison of modelled and measured HOx concentrations reveals a systematic underprediction of OH as a function of NO. A large discrepancy of a factor 2.6 is found at the lowest NO concentration encountered (0.1 ppb), whereas the discrepancy becomes insignificant above 1 ppb NO. This study extends similar observations from the Pearl-River Delta (PRD) in South China to a more urban environment. The OH discrepancy at Yufa can be resolved, if NO-independent additional OH recycling is assumed in the model. The postulated Leuven Isoprene Mechanism (LIM) has the potential to explain the gap between modelled and measured OH at Beijing taking into account conservative error estimates, but lacks experimental confirmation. This and the hereby unresolved discrepancy at PRD suggest that other VOCs besides isoprene might be involved in the required, additional OH recycling. Fast primary production of ROx radicals up to 7 ppb h−1 was determined at Beijing which was dominated by the photolysis of O3, HONO, HCHO, and dicarbonyls. For a special case, 20 August, when the plume of Beijing city was encountered, a missing primary HOx source (about 3 ppb h−1) was determined under high NOx conditions similar to other urban areas like Mexico City. CAREBeijing2006 emphasizes the important role of OVOCs as a radical source and sink, and the need for further investigation of the chemical degradation of VOCs in order to better understand radical chemistry in VOC-rich air.

Black carbon (BC) aerosols alter the radiation budget both directly (by absorbing solar visible radiation) and indirectly (by acting as cloud condensation nuclei) and cause adverse health effects. The absorbing efficiency and direct radiative effect of BC strongly depend on its mass concentration (MBC) and type of emission source. In the present study, we report measurements of MBC at the Research Center for Advanced Science and Technology (RCAST), located at the center of the urban boundary of Tokyo, using an EC-OC analyzer from 2003 to 2005 and a filter-based Continuous Soot Monitoring System (COSMOS) during 2007–2010. The results indicate that MBC have decreased significantly from 2.6 μg m−3 to 0.5 μg m−3 (∼80% reduction) between 2003 and 2010. Vehicular emissions are the dominant source of BC in Tokyo, and the observed reduction in MBC is mainly attributed to the stringent regulations of particulate matter exhaust from vehicles imposed by the Japanese government. In addition, this observation is also supported from emission estimates using diurnal-weekly variations of MBC in Tokyo and explains the observed reduction to within about 20%. This is the first clear evidence of a significant reduction in BC emissions in Tokyo and shows that measures taken to reduce BC emissions from traffic sources have a strong effect on air quality in a mega-city and also reduce the climate impact of traffic emissions. We highlight the importance of long-term and reliable measurements in detecting BC trends and for the validation and regulation of emission control measures in mega-cities.

Ambient OH and HO2 concentrations were measured by laser induced fluorescence (LIF) during the PRIDE-PRD2006 (Program of Regional Integrated Experiments of Air Quality over the Pearl River Delta, 2006) campaign at a rural site downwind of the megacity of Guangzhou in Southern China. The observed OH concentrations reached daily peak values of (15–26) × 106 cm−3 which are among the highest values so far reported for urban and suburban areas. The observed OH shows a consistent high correlation with j(O1D) over a broad range of NOx conditions. The correlation cannot be reproduced by model simulations, indicating that OH stabilizing processes are missing in current models. The observed OH exhibited a weak dependence on NOx in contrast to model predictions. While modelled and measured OH agree well at NO mixing ratios above 1 ppb, a continuously increasing underprediction of the observed OH is found towards lower NO concentrations, reaching a factor of 8 at 0.02 ppb NO. A dependence of the modelled-to-measured OH ratio on isoprene cannot be concluded from the PRD data. However, the magnitude of the ratio fits into the isoprene dependent trend that was reported from other campaigns in forested regions. Hofzumahaus et al. (2009) proposed an unknown OH recycling process without NO, in order to explain the high OH levels at PRD in the presence of high VOC reactivity and low NO. Taking a recently discovered interference in the LIF measurement of HO2 into account, the need for an additional HO2 → OH recycling process persists, but the required source strength may be up to 20% larger than previously determined. Recently postulated isoprene mechanisms by Lelieveld et al. (2008) and Peeters and Müller (2010) lead to significant enhancements of OH expected for PRD, but an underprediction of the observed OH by a factor of two remains at low NO (0.1–0.2 ppb). If the photolysis of hydroperoxy aldehydes from isoprene is as efficient as proposed by Peeters and Müller (2010), the corresponding OH formation at PRD would be more important than the primary OH production from ozone and HONO. While the new isoprene mechanisms need to be confirmed by laboratory experiments, there is probably need for other, so far unidentified chemical processes to explain entirely the high OH levels observed in Southern China.

Both organic carbon (OC) and elemental carbon (EC) were measured during PRIDE-PRD 2006 summer campaign by using a semi-continuous thermal-optical carbon analyzer at a rural site, Back Garden (BG), which is located 50 km to the northwest of Guangzhou City. Together with the online EC/OC analyzer, various kinds of instruments related to aerosol chemical properties were employed here, which provided a good opportunity to check data quality. The concentrations of OC correlated well with the mass of organic matter (OM) and water soluble organic carbon (WSOC), implying the reliability of the data measured in this campaign. The average OC concentrations in fine particle for three typical periods during the campaign (local emission influence, typhoon and precipitation and normal days) were 28.1 μgC m−3, 4.0 μgC m−3 and 5.7 μgC m−3, respectively; and EC were 11.6 μgC m−3, 1.8 μgC m−3, and 3.3 μgC m−3, respectively. The diurnal patterns of EC and OC during the campaign were higher at night and in early morning than daytime, which was probably caused by the primary emission and accumulation in the occurrence of low boundary layer. Compared with the constant diurnal enhancement ratios of EC, the enhancement ratio of OC (OC versus (CO-CObackground)) kept in a relative high level in the afternoon, with a similar diurnal profile to oxygenated organic aerosol (OOA), due to the strong photochemical formation of OC. Here, a modified EC tracer method was used to estimate the formation of secondary organic carbon (SOC). These results showed that the average SOC concentration (normal days) at BG site was about 2.0 ± 2.3 μgC m−3, and the SOC fraction in OC could reach up to 80% with the average of 47%. The modified approach in this study proved to be effective and reliable for SOC estimation based on good correlations between estimated SOC versus OOA or WSOC, and estimated POC versus hydrocarbon-like organic aerosol (HOA).

We use ozone and carbon monoxide measurements from the Tropospheric Emission Spectrometer (TES), model estimates of Ozone, CO, and ozone pre-cursors from the Real-time Air Quality Modeling System (RAQMS), and data from the NASA DC8 aircraft to characterize the source and dynamical evolution of ozone and CO in Asian wildfire plumes during the spring ARCTAS campaign 2008. On the 19 April, NASA DC8 O3 and aerosol Differential Absorption Lidar (DIAL) observed two biomass burning plumes originating from North-Western Asia (Kazakhstan) and South-Eastern Asia (Thailand) that advected eastward over the Pacific reaching North America in 10 to 12 days. Using both TES observations and RAQMS chemical analyses, we track the wildfire plumes from their source to the ARCTAS DC8 platform. In addition to photochemical production due to ozone pre-cursors, we find that exchange between the stratosphere and the troposphere is a major factor influencing O3 concentrations for both plumes. For example, the Kazakhstan and Siberian plumes at 55 degrees North is a region of significant springtime stratospheric/tropospheric exchange. Stratospheric air influences the Thailand plume after it is lofted to high altitudes via the Himalayas. Using comparisons of the model to the aircraft and satellite measurements, we estimate that the Kazakhstan plume is responsible for increases of O3 and CO mixing ratios by approximately 6.4 ppbv and 38 ppbv in the lower troposphere (height of 2 to 6 km), and the Thailand plume is responsible for increases of O3 and CO mixing ratios of approximately 11 ppbv and 71 ppbv in the upper troposphere (height of 8 to 12 km) respectively. However, there are significant sources of uncertainty in these estimates that point to the need for future improvements in both model and satellite observations. For example, it is challenging to characterize the fraction of air parcels from the stratosphere versus those from the fire because of the low sensitivity of the TES CO estimates used to mark stratospheric air versus air parcels affected by the smoke plume. Model transport uncertainties, such as too much dispersion, results in a broad plume structure from the Kazakhstan fires that is approximately 2 km lower than the plume observed by aircraft. Consequently, the model and TES data do not capture the photochemical production of ozone in the Kazakhstan plume that is apparent in the aircraft in situ data. However, ozone and CO distributions from TES and RAQMS model estimates of the Thailand plume are within the uncertainties of the TES data. Therefore, the RAQMS model is better able to characterize the emissions from this fire, the mixing of ozone from the stratosphere to the plume, and the photochemical production and transport of ozone and ozone pre-cursors as the plume moves across the Pacific.

In order to characterize the features of particulate pollution in the Pearl River Delta (PRD) in the summer, continuous measurements of particle number size distributions and chemical compositions were simultaneously performed at Guangzhou urban site (GZ) and Back-garden downwind regional site (BG) in July 2006. Particle number concentration from 20 nm to 10 μm at BG was (1.7±0.8)×104 cm−3, about 40% lower than that at GZ, (2.9±1.1)×104 cm−3. The total particle volume concentration at BG was 94±34 μm3 cm−3, similar to that at GZ, 96±43 μm3 cm−3. More 20–100 nm particles, significantly affected by the traffic emissions, were observed at GZ, while 100–660 nm particle number concentrations were similar at both sites as they are more regional. PM2.5 values were similar at GZ (69±43 μg m−3) and BG (69±58 μg m−3) with R2 of 0.71 for the daily average PM2.5 at these two sites, indicating the fine particulate pollution in the PRD region to be regional. Two kinds of pollution episodes, the accumulation pollution episode and the regional transport pollution episode, were observed. Fine particles over 100 nm dominated both number and volume concentrations of total particles during the late periods of these pollution episodes. Accumulation and secondary transformation are the main reasons for the nighttime accumulation pollution episode. SO42−, NO3− accounted for about 60% in 100–660 nm particle mass and PM2.5 increase. When south or southeast wind prevailed in the PRD region, regional transport of pollutants took place. Regional transport contributed about 30% to fine particulate pollution at BG during a regional transport case. Secondary transformation played an important role during regional transport, causing higher increase rates of secondary ions in PM1.0 than other species and shifting the peaks of sulfate and ammonium mass size distributions to larger sizes. SO42−, NO3−, and NH4+ accounted for about 70% and 40% of PM1.0 and PM2.5, respectively.

In situ measurements of the mass concentration of black carbon (BC) and mixing ratios of carbon monoxide (CO) and carbon dioxide (CO2) were made at Guangzhou, an urban measurement site in the Pearl River Delta (PRD), China, in July 2006. The average ± standard deviation (SD) concentrations of BC, CO, and CO2 were 4.7± 2.3 μgC m−3, 798± 459 ppbv, and 400± 13 ppmv, respectively. The trends of these species were mainly controlled by synoptic-scale changes in meteorology during the campaign. Based on back trajectories, data are analyzed separately for two different air mass types representing northerly and southerly flows. The northerly air masses, which constituted ~25% of the campaign, originated mostly in the PRD and hence represent observations on regional scales. On the other hand, during southerly flow (~75%), the measurements were influenced by dilution due to cleaner marine air. The diurnal patterns of BC, CO, and CO2 exhibited peak concentrations during the morning and evening hours coinciding with rush-hour traffic. The ratios of OC/BC were lower during the morning hour peaks in the concentrations of primary pollutants due to their fresh emissions mainly from vehicular traffic in Guangzhou. The diurnal variations of BC observed in southerly air masses tended to follow the traffic patterns of heavy-duty vehicles (HDV) in Guangzhou, while the roles of other sources need to be investigated. The slopes of ΔBC/ΔCO, ΔBC/ΔCO2, and ΔCO/ΔCO2 observed during northerly flows were 0.0045 μgC m−3/ppbv, 0.13 μgC m−3/ppmv, and 49.4 ppbv/ppmv, respectively, agreeing reasonably with their respective emission ratios derived from regional emission inventories.

An airborne instrument for fast-response, high-precision measurement of tropospheric carbon monoxide (CO) was developed using a vacuum ultraviolet (VUV) resonance fluorescence technique. The excitation radiation is obtained by a DC discharge CO resonance lamp combined with an optical filter for the CO fourth positive band emission around 150 nm. The optical filter consists of a VUV monochromator and a crystalline quartz window (

Vertical profiles of HNO 3 , N 2 O, O 3 , and the aerosol extinction coefficient at 780 nm were observed by the Improved Limb Atmospheric Spectrometer (ILAS) on board the Advanced Earth Observing Satellite (ADEOS) during the Arctic winter of 1996-1997. Irreversible redistribution of HNO 3 is evaluated using HNO 3 -N 2 O and HNO 3 -O 3 correlations. Denitrification and nitrification started to be observed just after the Arctic vortex cooled to below the ice frost point (T ICE ) on February 10. Trajectory analyses show that denitrification occurred only in air masses, which were once cooled to near T ICE and were kept at temperatures below the nitric acid trihydrate saturation threshold continuously for more than 4 days. Such a temperature history provides the necessary conditions for nucleation and growth of particles causing denitrification. The average extent of denitrification at 19 km reached 43% at the center of the vortex, suggesting that stratospheric ozone could be affected by denitrification deep inside the vortex. Denitrification (>2 ppbv) and nitrification (> 1 ppbv) covered 40±10% and 35±10% of the vortex area, respectively. Redistributed numbers of HNO 3 molecules at each altitude were calculated by integrating the area-weighted changes in the HNO 3 concentration. The decreases in total HNO 3 concentration at 17-21 km in late February and early March agreed with the increases at 12-15 km to within 25%, confirming conservation of HNO 3 during sedimentation and evaporation of HNO 3 -containing polar stratospheric cloud particles.

Airborne observations of NO during the Subsonics Assessment Ozone and Nitrogen Oxides Experiment (SONEX) reveal episodes of high NOx in the upper troposphere believed to be associated with lightning. Linkage to specific periods of lightning activity is possible through back trajectories and data from the National Lightning Detection Network. Lagrangian model calculations are used to explore the evolution of these high NOx plumes over the 1–2 days between their introduction and subsequent sampling by NASA's DC-8 aircraft. Simulations include expected changes in HNO3, H2O2, CH3OOH, HO2, and OH. Depending on the time of injection and dilution rate, initial NOx concentrations are estimated to range from 1 to 7 ppbv. Similar to many previous studies, simulated HNO3 concentrations tend to be greater than observations. Several possible explanations for this difference are explored. H2O2 observations are shown to be consistent with removal in convective activity. While it is possible that upper tropospheric CH3OOH is enhanced by convection, simulations show such increases in CH3OOH can be short-lived (e.g.

The Improved Limb Atmospheric Spectrometer (ILAS), a solar occultation infrared satellite sensor, was launched in August 1996. The ILAS validation balloon campaigns were carried out from Kiruna, Sweden (68°N, 21°E), in February and March 1997 and Fairbanks, Alaska (65°N, 148°W), in April and May 1997. During these campaigns, measurements of nitric acid (HNO3) were made using infrared emission spectrometers (Cold Atmospheric Emission Spectral Radiometer, Michelson Interferometer for Passive Atmospheric Sounding-Balloon-Borne version 2, and farinfrared spectrometer) and infrared solar occultation spectrometers (Limb Profile Monitor of the Atmosphere and Mark IV interferometer). An in situ experiment (Chemiluminescence Detector) measured total reactive nitrogen (NOy,), from which HNO3 mixing ratios in the lower stratosphere were calculated. In addition, an in situ NOy, measurement was also made at 12 km altitude from the Deutsche Luft-und Raumfahrt Falcon aircraft in January 1997. The ILAS version 3.10 HNO3 mixing ratios obtained at the nearest location and averaged ILAS mixing ratios obtained within certain criteria were compared with the balloon data. The precision of the ILAS measurements was estimated from the random differences to be 0.8 parts per billion by volume (ppbv), corresponding to about 35% at 15 km and 10–15% at 20–35 km. While the absolute accuracy estimated from the systematic differences was as good as 0.5 ppbv (5%) at 20 km, the ILAS HNO3 mixing ratios were systematically lower than the balloon values by 1 ppbv (15–20%) at 25–30 km. The error in the altitude registration in the ILAS retrieval algorithm is a possible cause for the negative bias at higher altitudes.

Results of the comparison of carbon monoxide ground-based infrared solar spectroscopic measurements with data obtained during 1994 Measurement of Air Pollution From Space (MAPS) flights are presented. Spectroscopic measurements were performed correlatively with April and October MAPS flights by nine research groups from Belgium, Canada, Germany, Japan, New Zealand, Russia, and the United States. Characterization of the techniques and error analysis were performed. The role of the CO a priori profile used in the retrieval was estimated. In most cases an agreement between spectroscopic and MAPS data is within estimated MAPS accuracy of _+ 10%.

Measurements of NO, NO(y), O3, and CO were made during NASA's Global Tropospheric Experiment/Pacific Exploratory Mission-West B (GTE/PEM-West B) carried out over the western Pacific in February and March 1994. NO(x) was calculated from NO using a photostationary state model ((NO(x)(sub mc)). Correlations between these species are presented, and some insights into the sources of NO(x) and NO(y) are described. The boundaries between the lower, middle, and upper troposphere have been defined at potential temperatures of 311 K and 328 K, which correspond to the geometric altitudes of about 5 and 9 km at 30degN. Enhancements in the mixing ratios of NO(y) and CO were observed in the lower and middle troposphere. A positive correlation was found between these two species suggesting that the high NO(y) values were due to anthropogenic emissions over the continental surface. On the other hand, O3 increased little with increase in CO. As a result, NO(y)/O3 ratios were higher in air more influenced by pollution. NO(y), values in 55 and 28% of the air masses sampled in the lower and middle troposphere, respectively, were higher than the clean free tropospheric NO(y)-O3 range when O3 values simultaneously observed were used. High (NOx)mc/NOy ratios between 0.15 and 0.3 were found in the boundary layer with relatively low mixing ratios of CO and NOy during the three flights. These air masses were transported from a higher altitude (approximately 5 km) and a higher latitude (approximately 50degN) within a few days. The peroxyacetyl nitrate (PAN)/NO(y) ratios were generally high (approximately 0.4) in these air masses, and the thermal decomposition of PAN was a probable source of NO(x). In the middle troposphere the (NO(x))mc mixing ratio did not generally increase with NO(y) or CO, suggesting that the transport of air masses affected by anthropogenic emissions did not increase the NO(x) level significantly. In the upper troposphere, very minor effects from the continental surface sources were seen in the CO mixing ratio. By contrast, NO(y) values in 33% of the air masses were higher than those expected when stratospheric air intrusion is assumed to be a single source of NO(y) based on NO(y)-O3 correlation analyses. This result suggests significant free tropospheric NO(y) sources, namely exhaust from the aircraft and NO production by lightning activity. In fact, spikes in the (NO(x))(sub m)c mixing ratios were observed near the aircraft corridor south of Tokyo at an altitude of 10 km. These two free tropospheric NO(x) sources were considered to be important in determining the levels of the upper tropospheric NO(x) and NO(y) during PEM-West B.

Latitudinal distributions of NO, NO(y), O3, CO, CH3I, and H2O mixing ratios at 8.9-12 km were obtained between 30deg N and 1deg S by DC-8 aircraft measurements made in February 1994 during Pacific Exploratory Mission-West B (PEM-West B). Very low NO(y), mixing ratios with a median value of 51 parts per trillion by volume (pptv) were observed at 9.5-12 km at 1deg N-14deg N during two flights made within 3 days. A very low median O3 mixing ratio of 19 parts per billion by volume (ppbv) and high mixing ratios of H2O and CH3I were simultaneously observed, suggesting that the low NO(y), values were probably due to the convective transport of air from the tropical marine boundary layer to this altitude. The median NO(y)/O3 ratio being a factor of 2 smaller than in the air masses in the tropical marine boundary layer might suggest the possibility that the heterogeneous removal of HNO3 during convective transport further reduced NO(y) levels. In addition to the measurements between 9.5 and 12 km, low values of NO(y) and O3 were observed between 4 and 12 km at 1deg N. Divergent wind fields at 200 and 1000 hPa and infrared (IR) cloud images show that there was large scale convection (greater than 1000 km x 1000 km) in the northeast of New Guinea Island centered around Odeg S and 150deg E as part of systematic convective activity of the Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ). This type of large scale convection could have transported air with low levels of NO(y) and O3 to the middle and upper troposphere over a wide area in the tropics. On the other hand, NO mixing ratios of 50-200 pptv and high NQ,/NOY ratios of 0.4-0.6 were observed at 9.5 km between 4deg S and 10deg S. High H2O Mixing ratios of 600-1200 parts per million by volume (ppmv) and low CO mixing ratios of 65 ppbv observed in the air mass indicated that the high NO values were probably due to NO production by lightning. Satellite observations showed relatively frequent lightning flashes over the New Guinea Island for 3 days prior to the aircraft measurements. These results are considered to be consistent with the idea that, in general, marine convection is not accompanied by lightning activity, whereas convection over land is. Because of the large areal extent of the influences from these processes, the convective transport of low NO(y) air and NO production by lightning should play critical roles in controlling the abundance of reactive nitrogen in the equatorial region.

Signatures of the N2O5 hydrolysis by sulfate aerosols have been previously documented, primarily from balloon and remote-sensing platforms, by measurements of nitrogen species aboard the NASA ER-2 flying at an altitude of approximately 20 km and some ER-2 and DC-8 measurements near the tropopause during stratospheric campaigns. This study documents such signatures in the NOx/NOy ratios derived from DC-8 measurements during Pacific Exploratory Measurements in the Western Pacific Ocean (PEM-West B) in stratospherically influenced air masses sampled during a level leg at an altitude of 10.7 km in flight 17 out of Japan. Despite the very low abundance of total bromine, we also show that heterogeneous hydrolysis of BrNO3 on sulphate aerosols can catalytically convert NOx and liquid H2O into HNO3 and OH and thereby lower the calculated equilibrium NOx/NOy by about 20 to 35% in these air masses, bringing closer agreement with the nitrogen partitioning deduced from measurements. However, the NOx/NOy ratios calculated from a model including heterogeneous chemistry were a factor of 3 smaller than ratios derived from data for a segment of this flight leg when DC-8 measurements indicated a stronger tropospheric influence. We also modeled the equilibrium partitioning of nitrogen species for all upper tropospheric air masses encountered by the DC-8; since NOy in the troposphere may contain nonnegligible contributions from long-lived nitrates (such as peroxyacetylnitrate), we have compared instead modeled and measured NOx/HNO3. The calculated equilibrium NOx/HNO3 ratios using only gas-phase chemistry are on the average smaller than those deduced from measurements in upper tropospheric air masses; inclusion of N2O5 hydrolysis reduces these ratios by an additional 20%, thus worsening the discrepancy. These results suggest a rapid transition from “denoxified” conditions in the lower stratosphere to “renoxified” conditions in the upper troposphere. This transition could be due to intrinsically different chemistry in the troposphere. Alternatively, rapid transport in the troposphere could keep the NOx and HNO3 away from chemical equilibrium. Detailed analysis of current and future tropospheric data could shed light on this issue.

Measurements of NO and NOy using a chemiluminescence technique were made on board a DC-8 aircraft during NASA's Pacific Exploratory Mission-West B (PEM-West B). The gold converter to convert NOy species into NO was operated at a constant pressure using a servo-controlled Teflon valve, which has been used for NOy measurements on board the ER-2 aircraft. The results of laboratory tests and some flight data during PEM-West B are presented. These experiments indicate no detectable inlet loss of HNO3 in dry air, although some loss was observed at H2O mixing ratios of 1–2%. The laboratory tests also showed small variability in the NOy artifact, high conversion efficiency for NO2 and HNO3, low HCN conversion efficiency, good repeatability of the measurements, and fast response. The control of the converter pressure during flight has been proven to be very advantageous in making reliable aircraft NOy measurements in the troposphere. The uncertainties of the NO and NOy PEM-West B data, including the effects of HCN conversion and HNO3 inlet loss, have been estimated.

This study examines the influence of photochemical processes on tropospheric ozone distributions over the extratropical western North Pacific. The analysis presented here is based on data collected during the Pacific Exploratory Mission-West Phase B (PEM-West B) field study conducted in February-March 1994. Sampling in the study region involved altitudes of 0-12 km and latitudes of 10deg S to 50deg N. The extratropical component of the data set (i.e., 20-50deg N) was defined by markedly different photochemical environments north and south of 30deg N. This separation was clearly defined by an abrupt decrease in the tropopause height near 30deg N and a concomitant increase in total O3 column density. This shift in overhead O3 led to highly reduced rates of O3 formation and destruction for the 30-50deg N latitude regime. Both latitude ranges, however, still exhibited net O3 production at all altitudes. Of special significance was the finding that net O3 production prevailed even at boundary layer and lower free tropospheric altitudes (e.g., less than 4 km), a condition uncommon to Pacific marine environments. These results reflect the strong impact of continental Outflow of O3 precursors (e.g., NO and NMHCS) into the northwestern Pacific Basin. Comparisons with PEM-West A, which sampled the same region in a different season (September-October), revealed major differences at altitudes below 4 km, the altitude range most influenced by continental outflow. The resulting net rate of increase in the tropospheric O3 column for PEM-West B was 1-3 % per day, while for PEM-West A it was approximately zero. Unique to the PEM-West B study is the finding that even under wintertime conditions substantial column production of tropospheric O3 can occur at subtropical and mid-latitudes. While such impacts may not be totally unexpected at near coast locations, the present study suggests that the impact from continental outflow on the marine BL could extend out to distances of more than 2000 km from the Asian Pacific Rim.

NO mixing ratios measured from Kiruna (68°N, 20°E), Sweden, on January 22, 1992, revealed values much smaller than those observed at midlatitude near equinox and had a sharper vertical gradient around 25 km. Location of the measurements was close to the terminator and near the edge of the polar vortex, which is highly distorted from concentric flow by strong planetary wave activities. These conditions necessitate accurate calculation, properly taking into account the transport and photochemical processes, in order to quantitatively explain the observed NO profile. A three-dimensional chemistry and transport model (CTM) and a trajectory model (TM) were used to interpret the profile observations within their larger spatial, temporal, and chemical context. The NOy profile calculated by the CTM is in good agreement with that observed on January 31, 1992. In addition, model NOy profiles show small variabilities depending on latitudes, and they change little between January 22 and 31. The TM uses the observed NOy values. The NO values calculated by the CTM and TM agree with observations up to 27 km. Between 20 and 27 km the NO values calculated by the trajectory model including only gas phase chemistry are much larger than those including heterogeneous chemistry, indicating that NO mixing ratios were reduced significantly by heterogeneous chemistry on sulfuric acid aerosols. Very little sunlight to generate NOx from HNO3 was available, also causing the very low NO values. The good agreement between the observed and modeled NO profiles indicates that models can reproduce the photochemical and transport processes in the region where NO values have a sharp horizontal gradient. Moreover, CTM and TM model results show that even when the NOy gradients are weak, the model NO depends upon accurate calculation of the transport and insolation for several days.

Remote and in situ measurements of gases and aerosols were made with airborne instrumentation to investigate the sources and sinks of tropospheric gases and aerosols over the western Pacific during the NASA Global Tropospheric Experiment (GTE)/Pacific Exploratory Mission-West A (PEM-West A) conducted in September–October 1991. This paper discusses the general characteristics of the air masses encountered during this experiment using an airborne lidar system for measurements of the large-scale variations in ozone (O3) and aerosol distributions across the troposphere and airborne in situ instrumentation for comprehensive measurements of air mass composition. In low latitudes of the western Pacific the airflow was generally from the east, and under these conditions the air was observed to have low aerosol loading and low ozone levels throughout the troposphere. Ozone was found to be below 10 parts per billion volume (ppbv) near the surface to 40–50 ppbv in the middle to upper troposphere. In the middle and high latitudes the airflow was mostly westerly, and the background O3 was generally less than 55 ppbv. On 60% of the PEM-West A flights, O3 was observed to exceed these levels in regions that were determined to be associated with stratospheric intrusions. In convective outflows from typhoons, near-surface air with low ozone ( 10 km). Several cases of continental plumes from Asia were observed over the Pacific during westerly flow conditions. These plumes were found in the lower troposphere with ozone levels in the 60–80 ppbv range and enhanced aerosol scattering. At low latitudes over the central Pacific the troposphere primarily contained air with background or low ozone levels; however, stratospherically influenced air with enhanced ozone (40–60 ppbv) was observed several times in the lower troposphere. The frequency of observation of the air masses and their average chemical composition are also discussed in this paper.

The Pacific Ocean is one of the few remaining regions of the northern hemisphere that is relatively free of direct anthropogenic emissions. However, long-range transport of air pollutants is beginning to have a significant impact on the atmosphere over the Pacific. In September and October 1991, NASA conducted the Pacific Exploratory Mission-West A expedition to study the atmospheric chemistry and background budgets of key atmospheric trace species. Aircraft sampling centered on the northern Pacific, 0° to 40°N and 115° to 180°E. The paper summarizes the chemical signature of relatively well-aged Pacific marine air (residence time ≥10 days over the ocean). The chemical signatures show that marine air is not always devoid of continental influences. Aged marine air which circulates around the semipermanent subtropical anticyclone located off the Asian continent is influenced by infusion of continental air with anthropogenic emissions. The infusion occurs as the result of Asian outflow swept off the continent behind eastward moving cold fronts. When compared to aged marine air with a more southerly pathway, this infusion results in enhancements in the mixing ratio of many anthropogenic/continental species and typically those with lifetimes of weeks in the free troposphere. Less enhancement is seen for the short-lived species with lifetimes of a few days as infused continental emissions are depleted during transport (about a week) around the semipermanent subtropical high.

The DC-8 mission of September 27, 1991, was designed to sample air flowing into Typhoon Mireille in the boundary layer, air in the upper tropospheric eye region, and air emerging from the typhoon and ahead of the system, also in the upper troposphere. The objective was to find how a typhoon redistributes trace constituents in the West Pacific region and whether any such redistribution is important on the global scale. The boundary layer air (300 m), in a region to the SE of the eye, contained low mixing ratios of the tracer species 03, CO, C2H6, C2H2, C3H8, C6H6 and CS2 but high values of dimethylsulfide (DMS). The eye region relative to the boundary layer, showed somewhat elevated levels of CO, substantially increased levels of 03, CS2 and all nonmethane hydrocarbons (NMHCs), and somewhat reduced levels of DMS. Ahead of the eye, CO and the NMHCs remained unchanged, 03 and CS2 showed a modest decrease, and DMS showed a substantial decrease. There was no evidence from lidar cross sections of ozone for the downward entrainment of stratospheric air into the eye region; these sections show that low ozone values were measured in the troposphere. The DMS data suggest sub- stantial entrainment of boundary layer air into the system, particularly into the eye wall region. Estimates of the DMS sulphur flux between the boundary layer and the free tro- posphere, based on computations of velocity potential and divergent winds, gave values of about 69 gg S m -2 d-averaged over a 17.5 o grid square encompassing the typhoon. A few hours aer sampling with the DC-8, Mireille passed over Oki Island, just to the north of Japan, producing surface values of ozone of 5.5 ppbv. These 03 levels are consistent with the low tropospheric values found by lidar and are more typical of equatorial regions. We suggest that the central eye region may act like a Taylor column which has moved poleward from low latitudes. The high-altitude photochemical environment within Typhoon Mireille was found to be quite active as evidenced by significant levels of measured gas phase H202 and CH300H and model-computed levels of OH.

[1] We evaluate the impact of transport from midlatitudes on aerosol number concentrations in the accumulation mode (light‐scattering particles (LSP) with diameters >180 nm) in the Arctic during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign. We focus on transport from the Asian continent. We find marked contrasts in the number concentration (NLSP), transport efficiency (TEN_LSP, the fraction transported from sources to the Arctic), size distribution, and the chemical composition of aerosols between air parcels from anthropogenic sources in East Asia (Asian AN) and biomass burning sources in Russia and Kazakhstan (Russian BB). Asian AN air had lower NLSP and TEN_LSP (25 cm �3 and 18% in spring and 6.2 cm �3 and 3.0% in summer) than Russian BB air (280 cm �3 and 97% in spring and 36 cm �3 and 7.6% in summer) due to more efficient wet scavenging during transport from East Asia. Russian BB in this spring is the most important source of accumulation‐mode aerosols over the Arctic, and BB emissions are found to be the primary source of aerosols within all the data in spring during ARCTAS. On the other hand, the contribution of Asian AN transport had a negligible effect on the accumulation‐mode aerosol number concentration in the Arctic during ARCTAS. Compared with background air, NLSP was 2.3–4.7 times greater for Russian BB air but 2.4–2.6 times less for Asian AN air in both spring and summer. This result shows that the transport of Asian AN air decreases aerosol number concentrations in the Arctic, despite the large emissions of aerosols in East Asia. The very low aerosol number concentrations in Asian AN air were caused by wet removal during vertical transport in association with warm conveyor belts (WCBs). Therefore, this cleansing effect will be prominent for air transported via WCBs from other midlatitude regions and seasons. The inflow of clean midlatitude air can potentially have an important impact on accumulation‐mode aerosol number concentrations in the Arctic. Citation: Matsui, H., et al. (2011), Accumulation‐mode aerosol number concentrations in the Arctic during the ARCTAS aircraft campaign: Long‐range transport of polluted and clean air from the Asian continent, J. Geophys. Res., 116, D20217, doi:10.1029/2011JD016189.

In the spring of 2008 NASA and NOAA funded the ARCTAS and ARCPAC field campaigns as contributions to POLARCAT, a core IPY activity. During the campaigns the NASA DC-8, P-3B and NOAA WP-3D aircraft conducted over 160 h of in-situ sampling between 0.1 and 12 km throughout the Western Arctic north of 55° N (i.e. Alaska to Greenland). All aircraft were equipped with multiple wavelength measurements of aerosol optics, trace gas and aerosol chemistry measurements, as well as direct measurements of the aerosol size distributions and black carbon mass. Late April of 2008 proved to be exceptional in terms of Asian biomass burning emissions transported to the Western Arctic. Though these smoke plumes account for only 11–14 % of the samples within the Western Arctic domain, they account for 42–47 % of the total burden of black carbon. Dust was also commonly observed but only contributes to 4–12 % and 3–8 % of total light absorption at 470 and 530 nm wavelengths above 6 km. Below 6 km, light absorption by carbonaceous aerosol derived from urban/industrial and biomass burning emissions account for 97–99 % of total light absorption by aerosol. Stratifying the data to reduce the influence of dust allows us to determine mass absorption efficiencies for black carbon of 11.2±0.8, 9.5±0.6 and 7.4±0.7 m2 g−1 at 470, 530 and 660 nm wavelengths. These estimates are consistent with 35–80 % enhancements in 530 nm absorption due to clear or slightly absorbing coatings of pure black carbon particulate. Assuming a 1/λ wavelength dependence for BC absorption, and assuming that refractory aerosol (420 °C, τ = 0.1 s) in low-dust samples is dominated by brown carbon, we derive mass absorption efficiencies for brown carbon of 0.83±0.15 and 0.27±0.08 m2 g−1 at 470 and 530 nm wavelengths. Estimates for the mass absorption efficiencies of Asian dust are 0.034 m2 g−1 and 0.017 m2 g−1. However the absorption efficiency estimates for dust are highly uncertain due to the limitations imposed by PSAP instrument noise. In-situ ARCTAS/ARCPAC measurements during the IPY provide valuable constraints for absorbing aerosol over the Western Arctic, species which are currently poorly simulated over a region that is critically under-sampled.

scale of about 1000 � 1000 km 2 under an anticyclonic pressure system. This air mass was transported northward fromthe high anthropogenic emission area extending south of Beijing with continuous photochemical production. Subsequent cold front passage broughtclean airfromthenorth,andpollutedairaround Beijingwassweptto thesouth of Beijing. This cycle was repeated about once a week and was found to be responsible for observed enhancements/reductions of aerosols at the intensive measurement sites. In contrast to secondary aerosols,the spatial distributions of primary aerosols (EC) reflected those of emissions, resulting in only slight variability despite the changes in synopticscale meteorology. In accordance with these results, source apportionment simulations revealed that primary aerosols around Beijing were controlled by emissions within 100 km around Beijing within the preceding 24 h, while emissions as far as 500 km and within the preceding 3 days were found to affect secondary aerosols.

[1] Organic carbon (OC) and elemental carbon (EC) in PM2.5 were measured hourly with a semicontinuous thermal-optical analyzer in Beijing, China, during four seasons from November 2005 to October 2006. The average OC concentrations measured at Peking University (PKU) site in urban Beijing were 20 ± 19, 12 ± 7, 10 ± 5, and 18 ± 11 μgC/m3 in winter, spring, summer, and autumn, respectively. Distinct seasonal and diurnal patterns of OC were observed, and their concentrations were significantly influenced by the seasonal and diurnal changes in sources, emission rates, and mesoscale meteorology. The impacts of meteorological parameters such as wind and precipitation on OC and EC concentrations are also discussed. OC and EC concentrations were found to be well correlated in winter, spring, and autumn, indicating their common origins, while their correlation was poorer in summer, especially in the afternoon, indicating that the influence of secondary organic carbon (SOC) was significant for this period. SOC concentrations were estimated by using the EC-tracer method as about 2.6 ± 3.1, 2.8 ± 2.4, 4.5 ± 2.9, and 4.1 ± 4.0 μgC/m3, accounting for 19%, 27%, 45%, and 23% of total organic carbon in winter, spring, summer, and autumn, respectively. This result showed that the relative contribution of SOC to OC in PM2.5 at this urban location was only comparable to that of primary organic carbon (POC) to OC in summer, while in the other three seasons, OC was dominated by POC.

This study was part of the international field measurement Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006). We investigated a new particle formation event in a highly polluted air mass at a regional site south of the megacity Beijing and its impact on the abundance and properties of cloud condensation nuclei (CCN). During the 1-month observation, particle nucleation followed by significant particle growth on a regional scale was observed frequently (similar to 30%), and we chose 23 August 2006 as a representative case study. Secondary aerosol mass was produced continuously, with sulfate, ammonium, and organics as major components. The aerosol mass growth rate was on average 19 mu g m(-3) h(-1) during the late hours of the day. This growth rate was observed several times during the 1-month intensive measurements. The nucleation mode grew very quickly into the size range of CCN, and the CCN size distribution was dominated by the growing nucleation mode ( up to 80% of the total CCN number concentration) and not as usual by the accumulation mode. At water vapor supersaturations of 0.07-0.86%, the CCN number concentrations reached maximum values of 4000-19,000 cm(-3) only 6-14 h after the nucleation event. During particle formation and growth, the effective hygroscopicity parameter kappa increased from about 0.1-0.3 to 0.35-0.5 for particles with diameters of 40-90 nm, but it remained nearly constant at similar to 0.45 for particles with diameters of similar to 190 nm. This result is consistent with aerosol chemical composition data, showing a pronounced increase of sulfate.

Total atmospheric OH reactivities (kOH) have been measured as reciprocal OH lifetimes by a newly developed instrument at a rural site in the densely populated Pearl River Delta (PRD) in Southern China in summer 2006. The deployed technique, LP-LIF, uses laser flash photolysis (LP) for artificial OH generation and laser-induced fluorescence (LIF) to measure the time-dependent OH decay in samples of ambient air. The reactivities observed at PRD covered a range from 10 s−1 to 120 s−1, indicating a large load of chemical reactants. On average, kOH exhibited a pronounced diurnal profile with a mean maximum value of 50 s−1 at daybreak and a mean minimum value of 20 s−1 at noon. The comparison of reactivities calculated from measured trace gases with measured kOH reveals a missing reactivity of about a factor of 2 at day and night. The reactivity explained by measured trace gases was dominated by anthropogenic pollutants (e.g., CO, NOx, light alkenes and aromatic hydrocarbons) at night, while it was strongly influenced by local, biogenic emissions of isoprene during the day. Box model calculations initialized by measured parameters reproduce the observed OH reactivity well and suggest that the missing reactivity is contributed by unmeasured, secondary chemistry products (mainly aldehydes and ketones) that were photochemically formed by hydrocarbon oxidation. Overall, kOH was dominated by organic compounds, which had a maximum contribution of 85% in the afternoon. The paper demonstrates the usefulness of direct reactivity measurements, emphasizes the need for direct measurements of oxygenated organic compounds in atmospheric chemistry studies, and discusses uncertainties of the modelling of OVOC reactivities.

[1] Eighteen C2–C7 NMHCs (nonmethane hydrocarbons) were measured hourly during the Integrated Measurement Program for Aerosol and Oxidant Chemistry in Tokyo (IMPACT) measurement campaigns conducted in central Tokyo during four different periods (summer/autumn of 2003 and winter/summer of 2004). The ambient atmospheric concentrations of NMHCs showed an inverse correlation with wind speed and mixing height and were significantly affected by mesoscale weather conditions. The mixing ratio of isoprene tightly correlated with solar flux and temperature in summer, as it was dominantly emitted by the local vegetation. All the observed NMHCs except isoprene showed high correlation with each other in winter (r2 > 0.5), suggesting concurrent accumulation under stagnant condition and common sources. Emission ratios were calculated on the basis of the correlation with carbon monoxide and ethyne. Compared to the typical winter NMHC composition, during summer there was a significant increase (up to 7 times higher than wintertime) of C4–C5 alkanes from fuel evaporation; of C2–C3 alkenes, n-hexane and benzene from chemical industry; and of toluene from local manufacturers, reflecting the temperature dependence of these evaporative emissions. In addition to the online measurements in Tokyo, canister sampling at a suburban site (Kisai) followed by multidimensional GC analyses was conducted during the summer campaign in 2004. The atmospheric concentrations of longer-lived compounds (≥ several days) at Kisai showed the buildup under sea breeze circulation. The average ambient concentration of toluene was 2 times higher than that in central Tokyo, likely because of substantial emissions from local industries as reported in the prefectural statistics.

[ 1] Tropospheric carbon monoxide ( CO) was measured throughout 2001 using groundbased Fourier transform IR ( FTIR) spectrometers at Moshiri (44.4 degrees N) and Rikubetsu (43.5 degrees N) observatories in northern Japan, which are separated by 150 km. Seasonal and day-to-day variations of CO are studied using these data, and contributions from various CO sources are evaluated using three-dimensional global chemistry transport model (GEOS-CHEM) calculations. Seasonal maximum and minimum FTIR-derived tropospheric CO amounts occurred in April and September, respectively. The ratio of partial column amounts between the 0 - 4 and 0 - 12 km altitude ranges is found to be slightly greater in early spring. The GEOS-CHEM model calculations generally reproduce these observed features. Source-labeled CO model calculations suggest that the observed seasonal variation is caused by seasonal contributions from various sources, in addition to a seasonal change in chemical CO loss by OH. Changes in meteorological fields largely control the relative importance of various source contributions. The contributions from fossil fuel (FF) combustion in Asia and photochemical CO production have the greatest yearly averaged contribution at 1 km among the CO sources (31% each). The Asian FF contribution increases from winter to summer, because weak southwesterly wind in summer brings more Asian pollutants to the observation sites. The seasonal variation from photochemical CO production is small ( +/- 17% at 1 km), likely because of concurrent increases ( decreases) of photochemical production and loss rates in summer ( winter), with the largest contribution between August and December. The contribution from intercontinental transport of European FF combustion CO is found to be comparable to that of Asian FF sources in winter. Northwesterly wind around the Siberian high in this season brings pollutants from Europe directly to Japan, in addition to southward transport of accumulated pollution from higher latitudes. The influences are generally greater at lower altitudes, resulting in a vertical gradient in the CO profile during winter. The model underestimates total CO by 12 - 14% between March and June. Satellite-derived fire-count data and the relationship between FTIR-derived HCN and CO amounts are generally consistent with biomass burning influences, which could have been underestimated by the model calculations.

[1] Mass concentrations of elemental carbon (EC) in fine mode and mixing ratios of carbon monoxide (CO) were measured at the University of Tokyo campus in Tokyo in different seasons in 2003–2005. Measurements of EC were made using a semicontinuous thermal-optical analyzer. The mass concentrations of nonvolatile aerosol measured by the calibrated scanning mobility particle sizer combined with a heated inlet agreed with the independent EC measurements with a systematic difference of about 4%, demonstrating that the mass concentrations of nonvolatile aerosol well represent those for EC. A majority of the nonvolatile aerosol and therefore EC mass concentration was in volume equivalent diameters between 50 and 200 nm, peaking at around 130 nm. The correlation of EC and CO was generally compact throughout the measurement period because of the similarity in sources. The slope of the EC-CO correlation (ΔEC/ΔCO) is therefore a useful parameter in validating EC emission inventories. The EC concentration and ΔEC/ΔCO showed distinct diurnal variation. On weekdays, EC and ΔEC/ΔCO reached maximum values of about 3 μg m−3 and 9 ng m−3/parts per billion by volume, respectively, in the early morning (0400–0800 local time), when the traffic density of heavy-duty trucks with diesel engines was highest. In addition, these values were lower by a factor of 2 on Sundays. The heavy truck traffic showed similar diurnal and weekday/weekend variations, indicating that exhaust from diesel engines is an important source of EC. Monthly mean ΔEC/ΔCO showed a seasonal variation, reaching broad maximum values in spring-autumn and reaching minimum values in midwinter, following the seasonal variation in temperature, as observed in Maryland, United States (Chen et al., 2001). This temperature dependence is likely due to the temperature dependence of EC emissions from diesel engines on intake air temperature. More stringent regulation of emissions of particles from diesel cars started in the Tokyo Metropolitan Area in October 2003. The ΔEC/ΔCO values did not change, however, exceeding the natural variability (10%) after 1 year from the start of the new regulations, when the temperature dependence is taken into account. This indicates that the regulation of particle emissions in the Tokyo Metropolitan Area was not effective in reducing the EC concentrations after 1 year.

[1] Simultaneous measurements of speciated, total reactive nitrogen (NOy) and particulate NO3 (particle diameter

[1] A recently developed new particle formation (NPF)-explicit version of the Weather Research and Forecasting Chemistry (WRF-chem) model can explicitly calculate the growth and sink of nucleated clusters with 20 aerosol size bins from 1 nm to 10 µm in diameter. In this study, the model was used to investigate spatial and temporal variations in NPF event frequency and the concentrations of aerosols (condensation nuclei, CN) and cloud condensation nuclei (CCN) within the boundary layer in East Asia in spring 2009. We found a distinct north-south contrast in the NPF frequency and mechanism in East Asia. NPF occurred mainly during limited periods over certain regions between 30° and 45°N (northeast China, Korea, and Japan, including regions around the active volcanoes Miyakejima and Sakurajima). In these latitudes, NPF was suppressed by high concentrations of preexisting particles under stagnant air conditions associated with high-pressure systems, although nucleation occurred more extensively during most of the simulation period. In contrast, south of 30°N, nucleation and NPF were both infrequent because of low SO2 emissions and H2SO4 concentrations. The period-averaged NPF frequency at 30°–45°N was three times that at 20°–30°N. This north-south contrast in NPF frequency was validated by surface measurements in outflow regions of East Asia. The simulated period- and domain-averaged contribution of secondary particles was estimated to be 44% for CN (>10 nm) and 26% for CCN at a supersaturation of 1.0%, though the contribution was highly sensitive to the amount and size distribution of primary aerosol emissions and the rate coefficient of the nucleation parameterization.

[1] The Pacific Exploration of Asian Continental Emission phase B (PEACE-B) aircraft mission was conducted over the western Pacific during April–May 2002. During several flights, large enhancements of CO greater than 200 parts per billion by volume (ppbv) were observed at altitudes between 5 and 10 km. In this paper, we describe vertical transport mechanisms over east Asia that were responsible for these enhancements, using the European Centre for Medium-Range Weather Forecasts (ECMWF) meteorological data and infrared cloud data obtained by the Geostationary Meteorological Satellite (GMS)-5. A case study for the highest CO event shows that it was likely due to vertical transport of pollutants caused by deep cumulus convection along a quasi-stationary frontal zone, which was formed over central China (around the Yangtze River at 30°N). In the mean meteorological field during the PEACE-B period, the warm, moist low-level southerlies converged into the frontal zone, sustaining cross-frontal temperature and moisture contrasts. Along the frontal zone, the mean vertical motion was distinctively upward, and a subtropical jet aloft was found to transport uplifted air parcels efficiently into the western Pacific. In this study, criteria to identify deep convection are defined using both the ECMWF and GMS data. The results show that convective activity, which was generally high below the subtropical jet, played an important role in producing updrafts over central China. The convective transport resulted mainly from a limited number of episodes, each of which followed the development of a weak cyclonic disturbance. Back trajectories of air parcels sampled at altitudes between 4 and 13 km on board the aircraft during PEACE-B show that among the air parcels originating from the 800-hPa level or below, 69% were likely to have undergone convective uplifting. In addition to convection, sloping isentropes often observed along the quasi-stationary jet axis yielded persistent slow quasi-adiabatic uplifting of air over the Far East, which was occasionally intensified with a classical warm conveyor belt (WCB) airstream on the passage of migratory cyclonic disturbances. Meteorological conditions during PEACE-B were thus favorable for the uplifting of boundary layer air influenced by anthropogenic emissions over central China. These results are consistent with the relatively high levels of Halon 1211 (CF2ClBr), a good tracer of Chinese anthropogenic emissions, observed in the air parcels that were likely uplifted in the frontal zone.

[1] Validation of the Measurements of Pollution in the Troposphere (MOPITT) retrievals of carbon monoxide (CO) has been performed with a varied set of correlative data. These include in situ observations from a regular program of aircraft observations at five sites ranging from the Arctic to the tropical South Pacific Ocean. Additional in situ profiles are available from several short-term research campaigns situated over North and South America, Africa, and the North and South Pacific Oceans. These correlative measurements are a crucial component of the validation of the retrieved CO profiles and columns from MOPITT. The current validation results indicate good quantitative agreement between MOPITT and in situ profiles, with an average bias less than 20 ppbv at all levels. Comparisons with measurements that were timed to sample profiles coincident with MOPITT overpasses show much less variability in the biases than those made by various groups as part of research field experiments. The validation results vary somewhat with location, as well as a change in the bias between the Phase 1 and Phase 2 retrievals (before and after a change in the instrument configuration due to a cooler failure). During Phase 1, a positive bias is found in the lower troposphere at cleaner locations, such as over the Pacific Ocean, with smaller biases at continental sites. However, the Phase 2 CO retrievals show a negative bias at the Pacific Ocean sites. These validation comparisons provide critical assessments of the retrievals and will be used, in conjunction with ongoing improvements to the retrieval algorithms, to further reduce the retrieval biases in future data versions.

[1] Aircraft measurements of ozone (O3) and its precursors (reactive nitrogen, CO, nonmethane hydrocarbons) were made over the western Pacific during the Transport and Chemical Evolution Over the Pacific (TRACE-P) campaign, which was conducted during February–April 2001. Biomass burning activity was high over Southeast Asia (SEA) during this period (dry season), and convective activity over SEA frequently transported air from the boundary layer to the free troposphere, followed by eastward transport to the sampling region over the western Pacific south of 30� N. This data set allows for systematic investigations of the chemical and physical processes in the outflow from SEA. Methyl chloride (CH3Cl) and CO are chosen as primary and secondary tracers, respectively, to gauge the degree of the impact of emissions of trace species from biomass burning. Biomass burning is found to be a major source of reactive nitrogen (NOx, PAN, HNO3, and nitrate) and O3 in this region from correlations of these species with the tracers. Changes in the abundance of reactive nitrogen during upward transport are quantified from the altitude change of the slopes of the correlations of these species with CO. NOx decreased with altitude due to its oxidation to HNO3. On the other hand, PAN was conserved during transport from the lower to the middle troposphere, consistent with its low water solubility and chemical stability at low temperatures. Large losses of HNO3 and nitrate, which are highly water soluble, occurred in the free troposphere, most likely due to wet removal by precipitation. This has been shown to be the major pathway of NOy loss in the middle troposphere. Increases in the mixing ratios of O3 and its precursors due to biomass burning in SEA are estimated using the tracers. Enhancements of CO and total reactive nitrogen (NOy), which are directly emitted from biomass burning, were largest at 2–4 km. At this altitudetheincreasesinNOyandO3were810partspertrillionbyvolume(pptv)and26parts per billion by volume (ppbv) above their background values of 240 pptv and 31 ppbv, respectively. The slope of the O3-CO correlation in biomass burning plumes was similar to those observed in fire plumes in northern Australia, Africa, and Canada. The O3 production efficiency (OPE) derived from the O3-CO slope and NOx/CO emission ratio (ER) is shown to be positively correlated with the C2H4/NOx ER, indicating that the C2H4/NOx ER is a critical parameter in determining the OPE. Comparison of the net O3 flux across the western Pacific region and total O3 production due to biomass burning in

[1] The current study provides a comparison of the photochemical environments for two NASA field studies focused on the western North Pacific (PEM-West-B (PWB) and TRACE-P (TP)). These two studies were separated in calendar time by approximately 7 years. Both studies were carried out under springtime conditions, with PWB being launched in 1994 and TP being deployed in 2001 (i.e., 23 February–15 March 1994 and 10 March–15 April 2001, respectively). Because of the 7-year time separation, these two studies presented a unique scientific opportunity to assess whether evidence could be found to support the Department of Energy's projections in 1997 that increases in anthropogenic emissions from East Asia could reach 5%/yr. Such projections would lead one to the conclusion that a significant shift in the atmospheric photochemical properties of the western North Pacific would occur. To the contrary, the findings from this study support the most recent emission inventory data [Streets et al., 2003] in that they show no significant systematic trend involving increases in any O3 precursor species and no evidence for a significant shift in the level of photochemical activity over the western North Pacific. This conclusion was reached in spite of there being real differences in the concentration levels of some species as well as differences in photochemical activity between PWB and TP. However, nearly all of these differences were shown to be a result of a near 3-week shift in TP's sampling window relative to PWB, thus placing it later in the spring season. The photochemical enhancements seen during TP were most noticeable for latitudes in the range of 25–45°N. Most important among these were increases in J(O1D), OH, and HO2 and values for photochemical ozone formation and destruction, all of which were typically two times larger than those calculated for PWB. A comparison of these airborne results with ozonesonde data from four Japanese stations provided further evidence showing that the 3-week shift in the respective sampling windows of PWB and TP was a likely cause for the differences seen in O3 levels and in photochemical activity between the two airborne studies.

[1] Measurements obtained during the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) experiment are used in conjunction with regional modeling analysis to evaluate emission estimates for Asia. A comparison between the modeled values and the observations is one method to evaluate emissions. Based on such analysis it is concluded that the inventory performs well for the light alkanes, CO, ethyne, SO2, and NOx. Furthermore, based on model skill in predicting important photochemical species such as O3, HCHO, OH, HO2, and HNO3, it is found that the emissions inventories are of sufficient quality to support preliminary studies of ozone production. These are important finding in light of the fact that emission estimates for many species (such as speciated NMHCs and BC) for this region have only recently been estimated and are highly uncertain. Using a classification of the measurements built upon trajectory analysis, we compare observed species distributions and ratios of species to those modeled and to ratios estimated from the emissions inventory. It is shown that this technique can reconstruct a spatial distribution of propane/benzene that looks remarkably similar to that calculated from the emissions inventory. A major discrepancy between modeled and observed behavior is found in the Yellow Sea, where modeled values are systematically underpredicted. The integrated analysis suggests that this may be related to an underestimation of emissions from the domestic sector. The emission is further tested by comparing observed and measured species ratios in identified megacity plumes. Many of the model derived ratios (e.g., BC/CO, SOx/C2H2) fall within ∼25% of those observed and all fall outside of a factor of 2.5.

[1] Data obtained during the TRACE-P experiment is used to evaluate how well the CFORS/STEM-2K1 regional-scale chemical transport model is able to represent the aircraft observations. Thirty-one calculated trace gas and aerosol parameters are presented and compared to the in situ data. The regional model is shown to accurately predict many of the important features observed. The mean values of all the model parameters in the lowest 1 km are predicted within ±30% of the observed values. The correlation coefficients (R) for the meteorological parameters are found to be higher than those for the trace species. For example, for temperature, R > 0.98. Among the trace species, ethane, propane, and ozone show the highest values (0.8 < R < 0.9), followed by CO, SO2, and NOy. NO and NO2 had the lowest values (R < 0.4). Analyses of pollutant transport into the Yellow Sea by frontal events are presented and illustrate the complex nature of outflow. Biomass burning from SE Asia is transported in the warm conveyor belt at altitudes above ∼2 km and at latitudes below 30N. Outflow of pollution emitted along the east coast of China in the postfrontal regions is typically confined to the lower ∼2 km and results in high concentrations with plume-like features in the Yellow Sea. During these situations the model underpredicts CO and black carbon (among other species). An analysis of ozone production in this region is also presented. In and around the highly industrialized regions of East Asia, where fossil fuel usage dominates, ozone is NMHC-limited. South of ∼30–35N, ozone production is NOx-limited, reflecting the high NMHC/NOx ratios due to the large contributions to the emissions from biomass burning, biogenics sources, and biofuel usage in central China and SE Asia.

[1] The NASA Langley Research Center and University of Wisconsin Regional Air Quality Modeling System (RAQMS) is used to estimate the tropospheric ozone budget over east Asia during the NASA Global Tropospheric Experiment (GTE) Transport and Chemical Evolution over the Pacific (TRACE-P) mission. The computed ozone budget explicitly accounts for stratosphere/troposphere exchange (STE) and in situ ozone production using on-line chemical calculations. The east Asian O3 budget is computed during the period from 7 March to 12 April 2001. Gross formation dominates STE by a ratio of 7 to 1 in east Asia during TRACE-P. However, this ratio is strongly influenced by altitude of the tropopause. Approximately 30% of the ozone that is advected across the tropopause over east Asia is subsequently advected out over the western Pacific within the upper 4 km of the troposphere by the Japan jet. The average net photochemical production (gross formation-gross destruction) within the regional domain is 0.37 Tg d−1 or 7% of the average flux at the eastern boundary of the domain during the TRACE-P time period. The budget analysis shows a very close balance between sources and sinks within the RAQMS regional domain during the TRACE-P time period. This balance results in very small average accumulation (∼1 Tg) of O3 in the east Asian region and very little net export averaged over the period (0.03 Tg d−1). The low ozone export from east Asia predicted by RAQMS during TRACE-P is a consequence of relatively high dry deposition rates, which are 37% of the gross ozone formation (1.469 Tg d−1) within the TRACE-P regional domain.

Measurements of HNO 3 mixing ratios from the chemical ionization mass spectrometer have been critically compared with simultaneous measurements of total gas phase NO y from the NO chemiluminescence detector aboard the NASA DC-8 aircraft during the SAGE 3 Ozone Loss and Validation Experiment (SOLVE). The data were obtained in the arctic upper troposphere and lower stratosphere in the winter of 1999-2000. A brief comparison to the NOy instrument aboard the NASA ER-2 is also presented. The time responses, detection limits, relative precision, and stability of relative calibrations for the instruments were in excellent agreement throughout the mission. However, the average slope of the HNO 3 to NO y correlation was 1.13 ± 0.03 overall and 1.06 ± 0.03 in stratospheric air, indicating that the two measurements had a systematic calibration offset. Possible sources for the offset error are presented, and methods to reduce the calibration error in future flights are suggested.

[1] We report the first in situ measurements of hydrogen cyanide (HCN) and methyl cyanide (CH3CN, acetonitrile) from the Pacific troposphere (0–12 km) obtained during the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) airborne mission (February–April 2001). Mean HCN and CH3CN mixing ratios of 243 ± 118 (median 218) ppt and 149 ± 56 (median 138) ppt, respectively, were measured. These in situ observations correspond to a mean tropospheric HCN column of 4.2 × 1015 molecules cm−2 and a CH3CN column of 2.5 × 1015 molecules cm−2. This is in good agreement with the 0–12 km HCN column of 4.4 (±0.6) × 1015 molecules cm−2 derived from infrared solar spectroscopic observations over Japan. Mixing ratios of HCN and CH3CN were greatly enhanced in pollution outflow from Asia and were well correlated with each other as well as with known tracers of biomass combustion (e.g., CH3Cl, CO). Volumetric enhancement (or emission) ratios (ERs) relative to CO in free tropospheric plumes, likely originating from fires, were 0.34% for HCN and 0.17% for CH3CN. ERs with respect to CH3Cl and CO in selected biomass burning (BB) plumes in the free troposphere and in boundary layer pollution episodes are used to estimate a global BB source of 0.8 ± 0.4 Tg (N) yr−1 for HCN and 0.4 ± 0.1 Tg (N) yr−1 for CH3CN. In comparison, emissions from industry and fossil fuel combustion are quite small (

[1] The NASA DC-8 and P-3B aircraft flew within about a kilometer or less of each other on three occasions during the Transport and Chemical Evolution Over the Pacific (TRACE-P) campaign in order to intercompare similar measurements on the two aircraft. The first and last intercomparisons were in relatively remote marine environments during transits to and from Asia. The first began with a boundary layer measurement followed by an ascent to 3 km. The second set of intercomparisons was at a fixed altitude of about 5.2 km off the coast of Japan, also in relatively clean air. Finally, the third measurement began at 5.3 km and then descended into the boundary layer. A number of measurements were compared with the best agreement observed for the most abundant compounds such as CO2 and CH4 and with very good agreement for CO, O3, and j values. Other comparisons, including measurements of the same compounds on both aircraft and measurements of the same compound by two different instruments on the DC-8, varied over a wide range from quite good for PAN, NO, HNO3, H2O; to reasonable agreement for OH, HO2 CH2O, acetone, and methylethylketone; and to generally poor for NO2,SO2, PPN, acetaldehyde, and methanol. The comparison results, particularly those for the fast 1-s CO and O3 measurements, suggest that credible intercomparisons can be made using two aircraft in close proximity for relatively long lifetime and stable compounds. Much new understanding can also be gained from measurements of more reactive and generally shorter lifetime compounds, but additional improvements are needed to make such studies as meaningful as those of longer lifetime compounds. Comparisons such as these, made as a component of a larger field campaign, have the advantage that they test the actual instrument configuration used during the field study and they require no additional instrument installation and testing.

[1] Peroxy radical concentrations were measured aboard the NASA P-3B aircraft during the Transport and Chemical Evolution over the Pacific (TRACE-P) campaign in the spring of 2001 and varied in ways that depended on radical production rates and reactive nitrogen concentrations. Measurements of HO2 ,H O2 +R O2, and OH during this study allowed calculation of radical ratios, examination of functional relationships of these ratios on controlling variables, and comparison with numerical model estimations. Radical production terms show changes in relative contributions at low, middle, and high total production rates that are understandable in terms of systematic variations in the controlling components (trace gas concentrations and photolysis rate coefficients). Ozone tendency calculations indicate net ozone production in the western Pacific basin because the concentrations of critical precursor trace gases (e.g., NOx, hydrocarbons) are highest there. The dependence of ozone tendency follows the concentration of NO systematically. Peroxy radical levels on the two aircraft (HO2 +R O2 on the P-3B and HO2 on the DC-8) during two relatively short prescribed intercomparison periods were in good agreement in one instance and poorer in another given reasonable assumptions about the apportioning of radicals between HO2 and RO2. Recommended changes to CH2O photolysis quantum yields, HO2 self reaction, and O( 1 D) quenching kinetics lead to small changes (

[1] The atmospheric CO2 mixing ratio was measured using a continuous measurement system onboard a Gulfstream-II aircraft between the northern midlatitudes and the southern subtropics during the Biomass Burning and Lightning Experiment Phase A (BIBLE A) campaign in September–October 1998. The vertical distribution of CO2 over tropical regions was almost constant from the surface to an altitude of 13 km. CO2 enhancements from biomass burning and oceanic release were observed in the tropical boundary layer. Measurements in the upper troposphere indicate interhemispheric exchange was effectively suppressed between 2°N–7°N. Interhemispheric transport of air in the upper troposphere was suppressed effectively in this region. The CO2 mixing ratios in the Northern and Southern Hemispheres were almost constant, with an average value of about 365 parts per million (ppm) and 366 ppm, respectively. The correlation between the CO2 and NOy mixing ratios observed north of 7°N was apparently different from that obtained south of 2°N. This fact strongly supports the result that the north-south boundary in the upper troposphere during BIBLE A was located around 2°N–7°N as the boundary is not necessary a permanent feature.

Measurements of total reactive odd nitrogen (NOy) and known individual odd nitrogen species were made over the Pacific Ocean in September and October 1991 during the NASA Global Tropospheric Experiment, Pacific Exploratory Mission-West A (GTE/PEM-West A). The ratios between NOx (NO + NO2) calculated from observed NO assuming photochemical equilibrium ((NOx)mc), peroxyacetyl nitrate (PAN), and NOy have been investigated for these data. The mixing ratios of (NOx)mc, PAN, and NOy in the lower and middle troposphere generally decreased with the air mass age, which has been defined by the propane/ethane ratio (C3H8/C2H6). The (NOx)mc/NOy ratios in the continental air showed a C-shaped vertical profile and median values were 0.27, 0.11, and 0.20 in the lower, middle, and upper troposphere, respectively. In the maritime and tropical air the (NOx)mc/NOy ratios generally increased with altitude and were about 0.1 and 0.15 in the lower and upper troposphere, respectively. In the middle troposphere the (NOx)mc/NOy ratios were similar in continental, maritime, and tropical air. These results are consistent with the fact that the (NOx)mc/NOy ratio did not decrease with the air mass age in the middle troposphere, suggesting the existence of NOx sources in the free troposphere. The PAN/NOy ratios in the continental air were about 0.3 at all altitudes. In maritime and tropical air the PAN/NOy ratio increased sharply at altitudes between 3 and 5 km with values of about 0.03 below 3 km and between 0.1 and 0.2 in the middle and upper troposphere. The PAN/NOy ratio generally decreased with the air mass age in the middle troposphere. In spite of a longer photochemical lifetime of PAN than NOx the PAN/(NOx)mc ratio also generally decreased with air mass age. These observations indicate that the reactive nitrogen ratios in the continental air mass are influenced by anthropogenic emissions at all altitudes, although relative contributions from various NOx sources in the upper troposphere are still poorly understood. Some influence from the continental air can be seen in the anthropogenic origin species in the maritime air mass when compared with the tropical air mass (Kondo et al., this issue). Similar (NOx)mc/NOy ratios, however, were generally found between the maritime and tropical air masses and a difference was only seen in the slightly higher PAN/NOy ratios in the maritime middle tropospheric air. The high-latitude air is characterized by low (NOx)mc/NOy ratios and high PAN/(NOx)mc ratios, probably due to the low atmospheric temperatures.

This study examines the influence of photochemical processes on ozone distributions in the western North Pacific. The analysis is based on data generated during NASA's western Pacific Exploratory Mission (PEM-West A) during the fall of 1991. Ozone trends were best described in terms of two geographical domains: the western North Pacific rim (WNPR) and the western tropical North Pacific (WTNP). For both geographical regions, ozone photochemical destruction, D(O3), decreased more rapidly with altitude than did photochemical formation, F(O3). Thus the ozone tendency, P(O3), was typically found to be negative for z 6–8 km. For nearly all altitudes and latitudes, observed nonmethane hydrocarbon (NMHC) levels were shown to be of minor importance as ozone precursor species. Air parcel types producing the largest positive values of P(O3) included fresh continental boundary layer (BL) air and high-altitude (z > 7 km) parcels influenced by deep convection/lightning. Significant negative P(O3) values were found when encountering clean marine BL air or relatively clean lower free-tropospheric air. Photochemical destruction and formation fluxes for the Pacific rim region were found to exceed average values cited for marine dry deposition and stratospheric injection in the northern hemisphere by nearly a factor of 6. This region was also found to be in near balance with respect to column-integrated O3 photochemical production and destruction. By contrast, for the tropical regime column-integrated O3 showed photochemical destruction exceeding production by nearly 80%. Both transport of O3 rich midlatitude air into the tropics as well as very high-altitude (10–17 km) photochemical O3 production were proposed as possible additional sources that might explain this estimated deficit. Results from this study further suggest that during the fall time period, deep convection over Asia and Malaysia/Indonesia provided a significant source of high-altitude NOx to the western Pacific. Given that the high-altitude NOx lifetime is estimated at between 3 and 9 days, one would predict that this source added significantly to high altitude photochemical O3 formation over large areas of the western Pacific. When viewed in terms of strong seasonal westerly flow, its influence would potentially span a large part of the Pacific.

[1] The Improved Limb Atmospheric Spectrometer-II (ILAS-II) was launched aboard the Advanced Earth Observing Satellite-II (ADEOS-II) in December 2002. Stratospheric vertical profiles of nitric acid (HNO3) concentration observed by ILAS-II (version 1.4) are validated using coincident HNO3 measurements by balloon-borne instruments (MIPAS-B2 and MkIV) in March and April 2003. Further validation is performed by making climatological comparisons of lower stratospheric HNO3-ozone (O3) correlations obtained by ILAS-II and ILAS (the predecessor of ILAS-II) for specific potential vorticity-based equivalent latitudes and seasons where and when ILAS data showed very compact correlations in 1997. The reduced scatter of ILAS-II HNO3 values around the reference HNO3, which is derived from ILAS-II O3 using the ILAS HNO3-O3 correlation, shows that the precision of the ILAS-II HNO3 data is better than 13–14%, 5%, and 1% at 15, 20, and 25 km, respectively. Combining all of the comparisons made in the present study, the accuracy of the ILAS-II HNO3 profiles at 15–25 km is estimated to be better than −13%/+26%.

[1] Data from 10 aircraft programs recorded over the central/eastern North Pacific (180°–120°W, 0°–45°N) were assembled for the purpose of assessing an atmospheric chemical climatology for this region. It represents an early effort at carrying out this task and, thus, it can be expected to undergo many updates in the future. Such a database is useful in both gaining further insights concerning the fundamental processes controlling the chemistry of this region as well as serving as an important baseline by which to evaluate future change. Critical photochemical precursors examined included O3, CO, NOx, and H2O. In addition, the distribution profiles for select nonmethane hydrocarbons were explored. The precursor data were analyzed according to latitude, pressure altitude, and season of the year. Contrasting the spring and fall measurements, major trends that surfaced in both ozone and CO included observing elevated levels in spring compared to fall, with the largest spring increase occurring at latitudes north of 15°N. Both NOx and H2O showed trends quite different from that of CO and O3, with an indication of higher mixing ratio levels during the fall season. Variations in precursor distribution patterns within a season will be explained based on climatological flow patterns for the region and the resulting connection to source regions. Where possible, comparisons were performed with other sampling strategies, including ground-based observations, sonde, and satellite data, and data collected during shuttle missions. Overall, these comparisons revealed a reasonably high level of correspondence between the airborne ensemble data and those collected using other sampling strategies.