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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] 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] 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.