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Oil sands mining and bitumen upgrading activities in the Athabasca Oil Sands Region (AOSR) have been identified as sources of metals and polycyclic aromatic compounds (PAC) being deposited to the regional snowpack. We performed an independent reanalysis of publicly available AOSR snow pack data to: replicate previous results; to provide new insights into the spatial and temporal patterns of metal and PAC deposition; and, to determine whether certain metals or PACs were associated with specific oil sands mining or upgrading activities. Using PAC ratios, we use a K-means clustering approach to classify snowpack data into two combustion-dominated classes, and three classes associated with oil sands mining and bitumen upgrading. Snow samples dominated by “oil sands mine” emissions are consistent with a petrogenic source and exhibited low UNS ratios and high DBT ratios. Snow samples dominated by “petroleum coke” emissions had the highest BaP ratios, high DBT ratios, and were collected nearest the upgrader complexes. Metals data indicate snow samples dominated by oil sands mine emissions are consistent with an Athabasca Sands type composition. Those dominated by emissions from petroleum coke show enrichment of biophile metals V, Ni, and M. We conclude that previous studies have over-estimated environmental loadings of PACs, their spatial extent, and direction of their trend over time. These differences are attributed to the use of arithmetic rather than geometric spatial averaging, use of an arbitrary location (AR6) to determine the extent of metals and PAC deposition, and because previous studies neglected to account for metals and PACs being deposited from non-oil sands sources. Oil sands operators continue to reduce their emissions intensity, however there is an emerging consensus that mitigating fugitive emissions from petroleum coke stockpiles may represent the greatest opportunity to reduce environmental loadings of PACs in the AOSR.

Life cycle greenhouse gas (GHG) emissions from the production of nuclear power (in g CO2e/kWh) are uncertain due partly to a paucity of data on emissions from individual phases of the nuclear fuel cycle. Here, we present the first comprehensive life cycle assessment of GHG emissions produced from the mining and milling of uranium in Canada. The study includes data from 2006-2013 for two uranium mine-mill operations in northern Saskatchewan (SK) and data from 1995-2010 for a third SK mine-mill operation. The mine-mill operations were determined to have GHG emissions intensities of 81, 64, and 34 kg CO2e/kg U3O8 at average ore grades of 0.74%, 1.54%, and 4.53% U3O8, respectively. The production-weighted average GHG emission intensity is 42 kg CO2e/kg U3O8 at an average ore grade of 3.81% U3O8. The production-weighted average GHG emission intensity drops to 24 kg CO2e/kg U3O8 when the local hydroelectric GHG emission factor (7.2 g CO2e/kWh) is substituted for the SK grid-average electricity GHG emission factor (768 g CO2e/kWh). This results in Canadian uranium mining-milling contributing only 1.1 g CO2e/kWh to total life cycle GHG emissions from the nuclear fuel cycle (0.7 g CO2e/kWh using the local hydroelectric emission factor).

We examine the relationship between the number concentration of boundary-layer cloud condensation nuclei (CCN) and light extinction to investigate underlying aerosol processes and satellite-based CCN estimates. For a variety of airborne and ground-based observations not dominated by dust, regression identifies the CCN (cm−3) at 0.4 ± 0.1% supersaturation with 100.3α +1.3σ0.75 where σ (Mm−1) is the 500 nm extinction coefficient by dried particles and α is the Angstrom exponent. The deviation of 1 km horizontal average data from this approximation is typically within a factor of 2.0. ∂logCCN / ∂logσ is less than unity because, among other explanations, growth processes generally make aerosols scatter more light without increasing their number. This, barring special meteorology–aerosol connections, associates a doubling of aerosol optical depth with less than a doubling of CCN, contrary to previous studies based on heavily averaged measurements or a satellite algorithm.

A modest operational program of systematic aircraft measurements can resolve key satellite aerosol data record limitations. Satellite observations provide frequent global aerosol amount maps but offer only loose aerosol property constraints needed for climate and air quality applications. We define and illustrate the feasibility of flying an aircraft payload to measure key aerosol optical, microphysical, and chemical properties in situ. The flight program could characterize major aerosol airmass types statistically, at a level of detail unobtainable from space. It would 1) enhance satellite aerosol retrieval products with better climatology assumptions and 2) improve translation between satellite-retrieved optical properties and species-specific aerosol mass and size simulated in climate models to assess aerosol forcing, its anthropogenic components, and other environmental impacts. As such, Systematic Aircraft Measurements to Characterize Aerosol Air Masses (SAM-CAAM) could add value to data records representing several decades of aerosol observations from space; improve aerosol constraints on climate modeling; help interrelate remote sensing, in situ, and modeling aerosol-type definitions; and contribute to future satellite aerosol missions. Fifteen required variables are identified and four payload options of increasing ambition are defined to constrain these quantities. “Option C” could meet all the SAM-CAAM objectives with about 20 instruments, most of which have flown before, but never routinely several times per week, and never as a group. Aircraft integration and approaches to data handling, payload support, and logistical considerations for a long-term, operational mission are discussed. SAM-CAAM is feasible because, for most aerosol sources and specified seasons, particle properties tend to be repeatable, even if aerosol loading varies.

During the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign, two NASA research aircraft, a DC-8 and a P-3B, were outfitted with extensive trace gas (the DC-8) and aerosol (both aircraft) instrumentation. Each aircraft spent about a half hour sampling air around the oil sands mining and upgrading facilities near Ft. McMurray, Alberta, Canada. The DC-8 circled the area, while the P-3B flew directly over the upgrading plants, sampling close to the exhaust stacks, then headed downwind to monitor the aerosol as it aged. At short range, the plume from the oil sands is a complex mosaic of freshly nucleated ultrafine particles from a SO2- and NO2-rich plume, soot and possibly fly ash from industrial processes, and dust from dirt roads and mining operations. Shortly downwind, organic aerosol appears in quantities that rival SO4, either as volatile organic vapors condense or as they react with the H2SO4. The DC-8 pattern allowed us to integrate total flux from the oil sands facilities within about a factor of 2 uncertainty that spanned values consistent with 2008 estimates from reported SO2 and NO2 emissions, though there is no reason to expect one flyby to represent average conditions. In contrast, CO fluxes exceeded reported regional emissions, due either to variability in production or sources missing from the emissions inventory. The conversion rate of SO2 to aerosol SO4 of ~6% per hour is consistent with earlier reports, though OH concentrations are insufficient to accomplish this. Other oxidation pathways must be active. Altogether, organic aerosol and black carbon emissions from the oil sands operations are small compared with annual forest fire emissions in Canada. The oil sands do contribute significant sulfate and exceed fire production of SO2 by an order of magnitude.

Accurate measurements of natural aerosol emissions over the ocean are needed to estimate the anthropogenic impact on the environment. In this study, we measured sea spray aerosol (SSA) concentrations with diameters larger than 0.040 μm produced by open-ocean breaking waves over the SEP (southeastern Pacific). Robust statistics were established through repeated airborne flights over 1000 km along 20° S from the coastline of Chile to 85° W during VOCALS-REx (VAMOS Ocean-Cloud-Atmosphere-Land-Study Regional Experiment). Non-volatile SSA number concentrations were inferred using a thermally resolved technique constrained for clean conditions with an Ångström exponent below 0.5, black carbon mass concentration at values lower than 15 ng m−3 and organic aerosol concentration less than 0.02 μg m−3. We found that number concentrations of SSAs active as cloud condensation nuclei (CCN) for a supersaturation of 0.25% varied between 17 and 36 cm−3, but these did not increase with the increasing mean wind speed typically observed further offshore along 20° S. Concurrent increases in mean offshore precipitation rate in excess of about 1 mm d−1 indicate that scavenging of SSAs by precipitation exceeds increases in production at wind speeds above about 8 m s−1. This demonstrates the critical role of precipitation as a major sink of SSA over the remote ocean. Finally, we found that under clean conditions and for estimated stratus supersaturations between 0.20 and 0.43%, SSA represented about 20% of the total potential CCN along 20° S.

Topography-induced steady-state accelerated wind flow in the Alenuihaha Channel between the islands of Hawaii and Maui provides about 100 km of fetch with winds that can nearly double over trade wind speed. Here ship- and aircraft-based observations of meteorological parameters and aerosols in Hawaii’s orographic natural “wind tunnel” are used for the study of sea salt aerosol (SSA) production, evolution, and related optical effects under clean oceanic conditions. There are certain advantages of channel measurements, such as a broad and uniform upstream area usually filled with background aerosol, stationary flow, and known fetch, but also some difficulties, like vigorous entrainment and persistent presence of organized structures (rolls). It is found that marine boundary layer (MBL) rolls are a common occurrence near the Hawaiian Islands even when cloud streets are not visible in satellite imagery. The presence of rolls tends to enhance the variability of ambient aerosol concentration and probably affects production of primary sea salt aerosol and entrainment from above. The possibility of channel measurements of the size-dependent flux of SSA is explored using a concentration buildup method as surface wind speeds range from 7 to 11 m s−1. Production of SSA particles with dry diameter as small as 0.18 μm was observed. General agreement with reported SSA fluxes was found.

Absorbing aerosols play an important, but uncertain, role in the global climate. Much of this uncertainty is due to a lack of adequate aerosol measurements. While great strides have been made in observational capability in the previous years and decades, it has become increasingly apparent that this development must continue. Scanning polarimeters have been designed to help resolve this issue by making accurate, multi-spectral, multi-angle polarized observations. This work involves the use of the Research Scanning Polarimeter (RSP). The RSP was designed as the airborne prototype for the Aerosol Polarimetery Sensor (APS), which was due to be launched as part of the (ultimately failed) NASA Glory mission. Field observations with the RSP, however, have established that simultaneous retrievals of aerosol absorption and vertical distribution over bright land surfaces are quite uncertain. We test a merger of RSP and High Spectral Resolution Lidar (HSRL) data with observations of boreal forest fire smoke, collected during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS). During ARCTAS, the RSP and HSRL instruments were mounted on the same aircraft, and validation data were provided by instruments on an aircraft flying a coordinated flight pattern. We found that the lidar data did indeed improve aerosol retrievals using an optimal estimation method, although not primarily because of the contraints imposed on the aerosol vertical distribution. The more useful piece of information from the HSRL was the total column aerosol optical depth, which was used to select the initial value (optimization starting point) of the aerosol number concentration. When ground based sun photometer network climatologies of number concentration were used as an initial value, we found that roughly half of the retrievals had unrealistic sizes and imaginary indices, even though the retrieved spectral optical depths agreed within uncertainties to independent observations. The convergence to an unrealistic local minimum by the optimal estimator is related to the relatively low sensitivity to particles smaller than 0.1 (μm) at large optical thicknesses. Thus, optimization algorithms used for operational aerosol retrievals of the fine mode size distribution, when the total optical depth is large, will require initial values generated from table look-ups that exclude unrealistic size/complex index mixtures. External constraints from lidar on initial values used in the optimal estimation methods will also be valuable in reducing the likelihood of obtaining spurious retrievals.

We describe aerosol optical depth (AOD) measured during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) experiment, focusing on vertical profiles, inter-comparison with correlative observations and fine-mode fraction. Arctic haze observed in 0.1. The retrieved fine-mode fraction of AOD is mostly between 0.7 and 1.0, and its root mean square difference (in both directions) from column-integral submicron fraction (measured with nephelometers, absorption photometers and an impactor) is 0.12. These AOD measurements from the NASA P-3 aircraft, after compensation for below-aircraft light attenuation by vertical extrapolation, mostly fall within ±0.02 of AERONET ground-based measurements between 340–1640 nm for five overpass events.

We use observations from the April 2008 NASA ARCTAS aircraft campaign to the North American Arctic, interpreted with a global 3-D chemical transport model (GEOS-Chem), to better understand the sources and cycling of hydrogen oxide radicals (HOx≡H+OH+peroxy radicals) and their reservoirs (HOy≡HOx+peroxides) in the springtime Arctic atmosphere. We find that a standard gas-phase chemical mechanism overestimates the observed HO2 and H2O2 concentrations. Computation of HOx and HOy gas-phase chemical budgets on the basis of the aircraft observations also indicates a large missing sink for both. We hypothesize that this could reflect HO2 uptake by aerosols, favored by low temperatures and relatively high aerosol loadings, through a mechanism that does not produce H2O2. We implemented such an uptake of HO2 by aerosol in the model using a standard reactive uptake coefficient parameterization with γ(HO2) values ranging from 0.02 at 275 K to 0.5 at 220 K. This successfully reproduces the concentrations and vertical distributions of the different HOx species and HOy reservoirs. HO2 uptake by aerosol is then a major HOx and HOy sink, decreasing mean OH and HO2 concentrations in the Arctic troposphere by 32% and 31% respectively. Better rate and product data for HO2 uptake by aerosol are needed to understand this role of aerosols in limiting the oxidizing power of the Arctic atmosphere.

Remote sensing of cloud condensation nuclei (CCN) would help evaluate the indirect effects of tropospheric aerosols on clouds and climate. To assess its feasibility, we examined relationships of submicron aerosol composition to CCN activity and optical properties observed during the MILAGRO/INTEX-B aircraft campaigns. An indicator of CCN activity, κ, was calculated from hygroscopicity measured under saturation. κ for dry 100 nm particles decreased with increasing organic fraction of non-refractory mass of submicron particles (OMF) as 0.34–0.20×OMF over Central Mexico and 0.47–0.43×OMF over the US West Coast. These fits represent the critical dry diameter, centered near 100 nm for 0.2% supersaturation but varied as κ(−1/3), within measurement uncertainty (~20%). The decreasing trends of CCN activity with the organic content, evident also in our direct CCN counts, were consistent with previous ground and laboratory observations of highly organic particles. The wider range of OMF, 0–0.8, for our research areas means that aerosol composition will be more critical for estimation of CCN concentration than at the fixed sites previously studied. Furthermore, the wavelength dependence of extinction was anti-correlated with OMF as −0.70×OMF+2.0 for Central Mexico's urban and industrial pollution air masses, for unclear reasons. The Angstrom exponent of absorption increased with OMF, more rapidly under higher single scattering albedo, as expected for the interplay between soot and colored weak absorbers (some organic species and dust). Because remote sensing products currently use the wavelength dependence of extinction albeit in the column integral form and may potentially include that of absorption, these regional spectral dependencies are expected to facilitate retrievals of aerosol bulk chemical composition and CCN activity over Central Mexico.

The NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) measures vertical profiles of aerosol extinction, backscatter, and depolarization at both 532 nm and 1064 nm. In March of 2006 the HSRL participated in the Megacity Initiative: Local and Global Research Observations (MILAGRO) campaign along with several other suites of instruments deployed on both aircraft and ground based platforms. This paper presents high spatial and vertical resolution HSRL measurements of aerosol extinction and optical depth from MILAGRO and comparisons of those measurements with similar measurements from other sensors and model predictions. HSRL measurements coincident with airborne in situ aerosol scattering and absorption measurements from two different instrument suites on the C-130 and G-1 aircraft, airborne aerosol optical depth (AOD) and extinction measurements from an airborne tracking sunphotometer on the J-31 aircraft, and AOD from a network of ground based Aerosol Robotic Network (AERONET) sun photometers are presented as a validation of the HSRL aerosol extinction and optical depth products. Regarding the extinction validation, we find bias differences between HSRL and these instruments to be less than 3% (0.01 km−1) at 532 nm, the wavelength at which the HSRL technique is employed. The rms differences at 532 nm were less than 50% (0.015 km−1). To our knowledge this is the most comprehensive validation of the HSRL measurement of aerosol extinction and optical depth to date. The observed bias differences in ambient aerosol extinction between HSRL and other measurements is within 15–20% at visible wavelengths, found by previous studies to be the differences observed with current state-of-the-art instrumentation (Schmid et al., 2006).

Submicron aerosol physical and chemical properties in remote marine air were measured from aircraft over the Southeast Pacific during VOCALS-REx in 2008 and the North Pacific during IMPEX in 2006, and aboard a ship in the Equatorial Pacific in 2009. A High Resolution – Particle Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) measured non-refractory submicron aerosol composition during all campaigns. Sulfate (SO4) and organics (Org), during VOCALS and the cruise show lower absolute values than those reported for previous "clean air" studies. In the marine boundary layer, average concentrations for SO4 were 0.52 μg m−3 for the VOCALS region and 0.85 μg m−3 for the equatorial region while average Org concentrations were 0.10 and 0.07 μg m−3, respectively. Campaign average Org/SO4 ratios were 0.19 (VOCALS) and 0.08 (equatorial Pacific). Black carbon (BC) measurements from a single particle soot photometer (SP2) and carbon monoxide (CO) concentrations over the Southeast Pacific provided sensitive indicators of pollution. CO and BC were used to identify the least polluted air, which had average concentrations of SO4 and Org of 0.14 and 0.01 μg m−3, respectively, with an average Org/SO4 of 0.08. Data from IMPEX was constrained to similar clean air criterion, and resulted in an average Org/SO4 ratio of 0.19. Under the cleanest MBL conditions during VOCALS, identified by CO below 61 ppbv, a robust linear relationship between Org and BC concentrations revealed that even at very low pollution levels, combustion sources dominated organic aerosol, suggesting little to no marine source of submicrometer Org to the atmosphere over the eastern South Pacific. This means marine organics cannot be identified by merely setting a standard for background conditions below which anthropogenic influence can be disregarded. Other methods must be used to exclude non-marine sources.

Dimethylsulfide (DMS) emitted from the ocean is a biogenic precursor gas for sulfur dioxide (SO2) and non-sea-salt sulfate aerosols (SO42−). During the VAMOS-Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in 2008, multiple instrumented platforms were deployed in the Southeastern Pacific (SEP) off the coast of Chile and Peru to study the linkage between aerosols and stratocumulus clouds. We present here observations from the NOAA Ship Ronald H. Brown and the NSF/NCAR C-130 aircraft along ~20° S from the coast (70° W) to a remote marine atmosphere (85° W). While SO42− and SO2 concentrations were distinctly elevated above background levels in the coastal marine boundary layer (MBL) due to anthropogenic influence (~800 and 80 pptv, respectively), their concentrations rapidly decreased west of 78° W (~100 and 25 pptv). In the remote region, entrainment from the free troposphere (FT) increased MBL SO2 burden at a rate of 0.05 ± 0.02 μmoles m−2 day−1 and diluted MBL SO42 burden at a rate of 0.5 ± 0.3 μmoles m−2 day−1, while the sea-to-air DMS flux (3.8 ± 0.4 μmoles m−2 day−1) remained the predominant source of sulfur mass to the MBL. In-cloud oxidation was found to be the most important mechanism for SO2 removal and in situ SO42− production. Surface SO42− concentration in the remote MBL displayed pronounced diel variability, increasing rapidly in the first few hours after sunset and decaying for the rest of the day. We theorize that the increase in SO42− was due to nighttime recoupling of the MBL that mixed down cloud-processed air, while decoupling and sporadic precipitation scavenging were responsible for the daytime decline in SO42−.

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.

[1] We use an ensemble of satellite (MODIS), aircraft, and ground-based aerosol observations during the ICARTT field campaign over eastern North America in summer 2004 to (1) examine the consistency between different aerosol measurements, (2) evaluate a new retrieval of aerosol optical depths (AODs) and inferred surface aerosol concentrations (PM2.5) from the MODIS satellite instrument, and (3) apply this collective information to improve our understanding of aerosol sources. The GEOS-Chem global chemical transport model (CTM) provides a transfer platform between the different data sets, allowing us to evaluate the consistency between different aerosol parameters observed at different times and locations. We use an improved MODIS AOD retrieval based on locally derived visible surface reflectances and aerosol properties calculated from GEOS-Chem. Use of GEOS-Chem aerosol optical properties in the MODIS retrieval not only results in an improved AOD product but also allows quantitative evaluation of model aerosol mass from the comparison of simulated and observed AODs. The aircraft measurements show narrower aerosol size distributions than those usually assumed in models, and this has important implications for AOD retrievals. Our MODIS AOD retrieval compares well to the ground-based AERONET data (R = 0.84, slope = 1.02), significantly improving on the MODIS c005 operational product. Inference of surface PM2.5 from our MODIS AOD retrieval shows good correlation to the EPA-AQS data (R = 0.78) but a high regression slope (slope = 1.48). The high slope is seen in all AOD-inferred PM2.5 concentrations (AERONET: slope = 2.04; MODIS c005: slope = 1.51) and could reflect a clear-sky bias in the AOD observations. The ensemble of MODIS, aircraft, and surface data are consistent in pointing to a model overestimate of sulfate in the mid-Atlantic and an underestimate of organic and dust aerosol in the southeastern United States. The sulfate overestimate could reflect an excessive contribution from aqueous-phase production in clouds, while the organic carbon underestimate could possibly be resolved by a new secondary pathway involving dicarbonyls.

A double-moment cloud microphysics scheme with a prognostic treatment of aerosols inside clouds has been implemented into the International Pacific Research Center Regional Atmospheric Model (iRAM) to simulate marine boundary layer clouds over the eastern Pacific and to study aerosol-cloud interactions, including the aerosol indirect effect. This paper describes the new model system and presents a comparison of model results with observations. The results show that iRAM with the double-moment cloud microphysics scheme is able to reproduce the major features, including the geographical patterns and vertical distribution of the basic cloud parameters such as cloud droplet number, liquid water content, or droplet effective radii over the eastern Pacific reasonably well. However, the model tends to underestimate cloud droplet number concentrations near the coastal regions strongly influenced by advection of continental aerosols and precursor gases. In addition, the average location of the stratocumulus deck off South America is shifted to the northwest compared with the satellite observations. We apply the new model system to assess the indirect aerosol effect over the eastern Pacific by comparing a simulation with preindustrial aerosol to an otherwise identical simulation with present-day aerosol. Resulting changes in the cloud droplet number concentration are particularly pronounced in Gulf of Mexico and along the Pacific coastlines with local changes up to 70 cm(-3) (50% of the present-day value). The modeled domain-averaged 3-month (August-October) mean change in top-of-atmosphere net cloud forcing over the ocean owing to changes in the aerosol burden by anthropogenic activities is -1.6W m(-2) (Less)

Measurements of CH2O from a tunable diode laser absorption spectrometer (TDLAS) were acquired onboard the NASA DC-8 during the summer 2004 INTEX-NA (Intercontinental Chemical Transport Experiment - North America) campaign to test our understanding of convection and production mechanisms in the upper troposphere (UT, 6-12-km) over continental North America and the North Atlantic Ocean. Point-by-point comparisons with box model calculations, when MHP (CH3OOH) measurements were available for model constraint, resulted in a median CH2O measurement/model ratio of 0.91 in the UT. Multiple tracers were used to arrive at a set of UT CH2O background and perturbed air mass periods, and 46% of the TDLAS measurements fell within the latter category. At least 66% to 73% of these elevated UT observations were caused by enhanced production from CH2O precursors rather than direct transport of CH2O from the boundary layer. This distinction is important, since the effects from the former can last for over a week or more compared to one day or less in the case of convective transport of CH2O itself. In general, production of CH2O from CH4 was found to be the dominant source term, even in perturbed air masses. This was followed by production from MHP, methanol, PAN type compounds, and ketones, in descending order of their contribution. In the presence of elevated NO from lightning and potentially from the stratosphere, there was a definite trend in the CH2O discrepancy, which for the highest NO mixing ratios produced a median CH2O measurement/model ratio of 3.9 in the 10-12-km range. Discrepancies in CH2O and HO2 in the UT with NO were highly correlated and this provided further information as to the possible mechanism(s) responsible. These discrepancies with NO are consistent with additional production sources of both gases involving CH3O2 + NO reactions, most likely caused by unmeasured hydrocarbons.

[1] We use data collected aboard the NASA DC-8 aircraft during the summer 2004, Intercontinental Transport and Chemical Evolution Experiment over North America (INTEX-NA) field campaign to examine the origin, composition, physical and optical properties of aerosols within air masses sampled over and downwind of the northeastern U.S. We note that aerosol concentrations within the region exhibited steep vertical gradients and significant variability in both time and space. An examination of air mass chemical signatures and backward trajectories indicates that transport from four, significantly different source regions contributed to the variability: the subtropical Atlantic Ocean (AO); the U.S. west coast and eastern Pacific (WCP); the U.S. east coast and Midwestern states (EC); and northwest Canada and Alaska (CA). AO air masses were typically confined to below 2 km altitude, exhibited low pollutant contents, contained enhanced levels of sea salt, and were typically observed when the Bermuda High strengthened. The most common air mass present in the upper troposphere, WCP air often contained weak dust and aged pollution enhances from convective input occurring over the central part of the continent. CA air exhibited enhancements in anthropogenic pollution tracers below 2 km and contained some black-carbon rich haze layers between 3 and 5 km that could be traced to forest fires burning in western Canada and Alaska. EC air was prevalent at lower elevations throughout the study area and exhibited enhanced scattering along with elevated levels of sulfate aerosols and combustion tracers. There is an overall balance between the observed cations and anions for all cases, except EC air mass below 4 km.

Gas phase HCl was measured from the marine boundary layer (MBL) to the lower stratosphere from the NASA DC-8 during five science flights (41 h) of the Intercontinental Chemical Transport Experiment-Phase B (INTEX-B) field campaign. In the upper troposphere/lower stratosphere (UT/LS, 8–12 km) HCl was observed to range from a few tens to 100 pptv due to stratospheric influence with a background tropospheric level of less than 2 pptv. In the 8–12 km altitude range, a simple analysis of the O3/HCl correlation shows that pure stratospheric and mixed tropospheric/stratospheric air masses were encountered 30% and 15% of the time, respectively. In the mid troposphere (4–8 km) HCl levels were usually below 2 pptv except for a few cases of stratospheric influence and were much lower than reported in previous work. These data indicate that background levels of HCl in the mid and upper troposphere are very low and confirm its use in these regions as a tracer of stratospheric ozone. However, a case study suggests that HCl may be produced in the mid troposphere by the dechlorination of dust aerosols. In the remote marine boundary layer HCl levels were consistently above 20 pptv (up to 140 pptv) and strongly correlated with HNO3. Cl atom levels were estimated from the background level of HCl in the MBL. This analysis suggests a Cl concentration of ~3×103 atoms cm−3, which corresponds to the lower range of previous studies. Finally, the observed HCl levels are compared to predictions by the Real-time Air Quality Modeling System (RAQMS) to assess its ability to characterize the impact of stratospheric transport on the upper troposphere.

[1] Aerosol column optical depth (AOD) is related to the aerosol direct radiative effect and readily available as a satellite product. The mass of dry aerosol up to 2.5 μm aerodynamic, or PM2.5, is a common measure of surface aerosol pollution at selected regional sites. A link between these two parameters would provide a way to infer PM2.5 and its change over extensive regions observed by satellites. This requires determination of the response of aerosol dry mass to the widely variable influence of ambient humidity and its optical contribution to column AOD. During the INTEX-North America aircraft campaign, we obtained 72 profiles of visible aerosol light scattering up to 10 km and its response to water uptake. The ambient AODs determined from these measurements, and confirmed for three profiles near surface AERONET, were generally below 0.4 except in the presence of a humid boundary layer with high aerosol loading. The fraction of ambient AOD due to water uptake, Wf, was found to be 37 ± 15% (average and standard deviation). Boundary layer PM2.5 was estimated (PM2.5proxy) from low-altitude size distributions measured from the aircraft. Despite the large variety of vertical aerosol structure, the ambient AOD was found correlated with the PM2.5proxy with R2 = 0.77, after 4% of data with AOD > 0.8 for >90% RH were removed. Our results support the application of remote sensing to retrievals of surface PM2.5 mass. The wavelength dependence of ambient AOD was found to be less effective in stratifying the mass versus extinction relationship on the column integral basis than on a layer by layer basis.

We present a statistical representation of the aggregate effects of deep convection on the chemistry and dynamics of the upper troposphere (UT) based on direct aircraft observations of the chemical composition of the UT over the eastern United States and Canada during summer. These measurements provide unique observational constraints on the chemistry occurring downwind of convection and the rate at which air in the UT is recycled. These results provide quantitative measures that can be used to evaluate global climate and chemistry models.

[1] An extensive set of aerosol physical and optical measurements was taken over the waters east of Asia during the Aerosol Characterization Experiment-Asia (ACE-Asia) project in the spring of 2001. Dust storms upwind of the study area combined with intense pollution plumes from coastal cities yielded an opportunity to examine both types of aerosol, in isolation and as they interacted. Scattering calculated from aerosol size distributions measured with an optical particle counter agreed well with simultaneous nephelometer measurements. We periodically heated sample air to evaporate sulfates and organic material. The change in volume upon heating agreed well with simultaneous measurements of aerosol composition. This volatile material was distributed on dust in rough proportion to surface area. Here we use the particle size and composition data to improve estimates of scattering at ambient humidity and to examine the effects of mixing on the optical properties of both pollution and dust aerosols. The presence of dust results in uptake of soluble and condensible species onto its surface and thereby reduces the mass scattering efficiency of the pollution aerosol by 50% and suppresses the change in scattering due to relative humidity (f(RH)) by up to 35%.

Previous laboratory and field studies suggest that oxidation of organic aerosols can be a source of oxygenated volatile organic compounds (OVOC). Using measurements of atmospheric oxidants and aerosol size distributions performed on the NASA DC-8 during the INTEX-NA campaign, we estimate the potential magnitude of the continental summertime OVOC flux from organic aerosol oxidation by OH to be as large as ∼70 pptv C/day in the free troposphere. Contributions from O_3, H_2O_2, photolysis, and other oxidants may increase this estimate. These processes may provide a large, diffuse source of OVOC that has not been included in current atmospheric models, and thus have a significant impact on our understanding of organic aerosol, OVOC, PAN, and HO_x chemistry. The potential importance and highly uncertain nature of our estimate highlights the need for more field and laboratory studies on organic aerosol composition and aging.

On five occasions spanning the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) field campaign in spring 2001, the Multiangle Imaging Spectroradiometer spaceborne instrument took data coincident with high-quality observations by instruments on two or more surface and airborne platforms. The cases capture a range of clean, polluted, and dusty aerosol conditions. With a three-stage optical modeling process, we synthesize the data from over 40 field instruments into layer-by-layer environmental snapshots that summarize what we know about the atmospheric and surface states at key locations during each event. We compare related measurements and discuss the implications of apparent discrepancies, at a level of detail appropriate for satellite retrieval algorithm and aerosol transport model validation. Aerosols within a few kilometers of the surface were composed primarily of pollution and Asian dust mixtures, as expected. Medium- and coarse-mode particle size distributions varied little among the events studied; however, column aerosol optical depth changed by more than a factor of 4, and the near-surface proportion of dust ranged between 25% and 50%. The amount of absorbing material in the submicron fraction was highest when near-surface winds crossed Beijing and the Korean Peninsula and was considerably lower for all other cases. Having simultaneous single-scattering albedo measurements at more than one wavelength would significantly reduce the remaining optical model uncertainties. The consistency of component particle microphysical properties among the five events, even in this relatively complex aerosol environment, suggests that global, satellite-derived maps of aerosol optical depth and aerosol mixture (air-mass-type) extent, combined with targeted in situ component microphysical property measurements, can provide a detailed global picture of aerosol behavior.

[1] Two major aircraft experiments occurred off the Pacific coast of Asia during spring 2001: the NASA sponsored Transport and Chemical Evolution over the Pacific (TRACE-P) and the National Science Foundation (NSF) sponsored Aerosol Characterization Experiment-Asia (ACE-Asia). Both experiments studied emissions from the Asian continent (biomass burning, urban/industrial pollution, and dust). TRACE-P focused on trace gases and aerosol during March/April and was based primarily in Hong Kong and Yokota Air Force Base, Japan, and involved two aircraft: the NASA DC-8 and the NASA P3-B. ACE-Asia focused on aerosol and radiation during April/May and was based in Iwakuni Marine Corps Air Station, Japan, and involved the NSF C-130. This paper compares aerosol measurements from these aircraft including aerosol concentrations, size distributions (and integral properties), chemistry, and optical properties. Best overall agreement (generally within RMS instrumental uncertainty) was for physical properties of the submircron aerosol, including condensation nuclei concentrations, scattering coefficients, and differential mobility analyzer and optical particle counter (OPC) accumulation mode size distributions. Larger differences (typically outside of the RMS uncertainty) were often observed for parameters related to the supermicron aerosols (total scattering and absorption coefficients, coarse mode Forward Scattering Spectrometer Probe and OPC size distributions/integral properties, and soluble chemical species usually associated with the largest particles, e.g., Na+, Cl−, Ca2+, and Mg2+), where aircraft sampling is more demanding. Some of the observed differences reflect different inlets (e.g., low-turbulence inlet enhancement of coarse mode aerosol), differences in sampling lines, and instrument configuration and design. Means and variances of comparable measurements for horizontal legs were calculated, and regression analyses were performed for each platform and allow for an assessment of instrument performance. These results provide a basis for integrating aerosol data from these aircraft platforms for both the TRACE-P and ACE-Asia experiments.

[1] Ground-based aerosol size distribution measurements at the Gosan, Korea, sampling site during ACE-Asia showed occasionally elevated concentrations of nucleation mode aerosol particles, with subsequent growth to the Aitken mode. Similar results from aircraft and ship-based measurements at around the same time indicated that at least one event exhibited a broad spatial extent. One of the most pronounced events, with total number concentrations of particles as high as 105 cm−3, occurred on 12 April at the same time as a large dust event, when the total aerosol surface area of particles with diameters less than 10 μm was increase by a factor of 1.7 compared to the average value for the study. Aircraft data showed layers of enlarged SO2 concentration coinciding with an increased aerosol total number concentration, with the highest detected SO2 concentration being 12 ppbv and aerosol number concentration reaching 8 × 104 cm−3 at 800 m altitude. Aircraft data showed that newly formed particles and dust were stratified in different layers in marine environment and transported to the surface close to the island. Atmospheric thermodynamic data suggested that particles were formed above the marine boundary layer and transported by vertical mixing toward the surface as a result of a 3 K north-to-south increase in the sea surface temperature. This temperature increase changed atmosphere stratification from stable to neutral/slightly unstable and deepened the internal mixed layer from below 300 m to above 800 m altitude. Measured hygroscopic properties of nucleation mode aerosol particles were consistent with those of ammonium sulfate particles. Here we reported a novel case study of tropospheric aerosol formation identifying particle chemical composition of nucleation mode aerosols in real time by measuring their water uptake properties. Then we demonstrated that particles formed in a layer aloft and were transported to the ground site by growth of the mixed boundary layer while nucleation was chemically induced and did not require turbulent mixing.

[1] During Transport and Chemical Evolution over the Pacific (TRACE-P) and Asian Aerosol Characterization Experiment (ACE-Asia) we measured the dry size distribution of Asian aerosols, their state of mixing, and the optical properties of dust, black carbon (BC) and other aerosol constituents in combustion and/or dust plumes. Optical particle sizing in association with thermal heating extracted volatile components and resolved sizes for dust and refractory soot that usually dominated light absorption. BC was internally mixed with volatile aerosol in � 85% of accumulation mode particles and constituted � 5–15% of their mass. These optically effective sizes constrained the soot and dust size distributions and the imaginary part of the dust refractive index, k, to 0.0006 ± 0.0001. This implies a single-scatter albedo, v (550 nm), for dust ranging from 0.99+ for Dp

areas as high as 1200 mm 2 cm � 3 . Concentrations of sulfuric acid generally appeared insufficient for binary nucleation, but observations, models, and theory are consistent with a ternary nucleation mechanism involving H2SO4-H2O-NH3. Growth rates of � 2n m h � 1 can be explained by the condensation of sulfuric acid at a rate of 2 ± 1 � 10 6 molecules cm � 3 s � 1 . Aerosol volatility suggested increasing neutralization of the aerosol during growth. Size distribution measurements suggest that weak (mean condensation nuclei (CN) 3–13 nm � 500 cm � 3 ) new particle production was a common occurrence in the region. However, new particle production was enhanced by � 1 order of magnitude (mean CN 3–13 nm � 5000 cm � 3 ) in postfrontal air masses associated with offshore flow during cloud-free conditions. Fog and clouds appear to be regionally important in modulating nucleation events through scavenging of secondary aerosol and through depletion of gas-phase precursors through enhanced heterogeneous chemistry. Our results indicate that only 10–30% of the total aerosol population consists of aged secondary aerosols after � 2 days of transport from source regions. In spite of their high production during nucleation events, secondary aerosols advected out over the Pacific Ocean will have a small impact upon indirect forcing and a negligible impact upon direct forcing compared to primary aerosol emissions and the species that condense upon them. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 4801 Oceanography: Biological and Chemical: Aerosols (0305); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; 9320 Information Related to Geographic Region: Asia

[1] During the ACE-Asia intensive observation period (IOP), an intercomparison experiment with ground-based lidars and aircraft observations was conducted near Tokyo. On 23 April 2001, four Mie backscatter lidars were simultaneously operated in the Tokyo region, while the National Center for Atmospheric Research C-130 aircraft flew a steppedascent profile between the surface and 6 km over Sagami Bay southwest of Tokyo. The C-130 observation package included a tracking Sun photometer and in situ packages measuring aerosol optical properties, aerosol size distribution, aerosol ionic composition, and SO2 concentration. The three polarization lidars suggested that the observed modest concentrations of Asian dust in the free troposphere extended up to an altitude of 8 km. We found a good agreement in the backscattering coefficient at 532 nm among lidars and in situ 180� backscatter nephelometer observations. The intercomparison indicated that the aerosol layer between 1.6 and 3.5 km was a remarkably stable and homogenous in mesoscale. We also found reasonable agreement between the aerosol extinction coefficients (sa � 0.03 km � 1 ) derived from the airborne tracking Sun photometer, in situ optical instruments, and those estimated from the lidars above the planetary boundary layer (PBL). We also found considerable vertical variation of the aerosol depolarization ratio (da) and a negative correlation between da and the backscattering coefficient (da) below 3.5 km. Airborne measurements of size-dependent optical parameters (e.g., the fine mode fraction of scattering) and of aerosol ionic compositions suggests that the mixing ratio of the accumulation-mode and coarse-mode (dust) aerosols was primarily responsible for the observed variation of da. Aerosol observations during the intercomparison period captured the following three types of layers in the atmosphere: a PBL (surface to 1.2–1.5 km) where fine (mainly sulfate) particles with a low da (

[1] Airborne measurements of aerosol light scattering (using nephelometers) and absorption (using particle/soot absorption photometers; PSAPs) in the Asian outflow region are presented. Aerosol particles were sampled through a new low turbulence inlet that proved very effective at transmitting coarse-mode particles. Noise and artifacts are characterized using in-flight measurements of particle-free air and measurements with identical instruments operated in parallel. For example, the sensitivities of PSAP noise to changing altitude, changing relative humidity (RH), and particle-loading on the internal filter are quantified. On the basis of these and previous instrument characterizations, we report averages, variations, and uncertainties of optical properties, focusing on data from approximately 300 level-leg samples obtained during 19 research flights in the spring of 2001. Several broad patterns emerge from this analysis. Two dominant components, fine-mode pollution and coarse-mode mineral dust, were observed to vary independently when separated using a cut point of 1 μm aerodynamic diameter at low RH. Fine-mode pollution was found to be moderately absorbing (single scatter albedo at low RH and 550 nm, ω = 0.88 ± 0.03; mean and 95% confidence uncertainty) and moderately hygroscopic (relative increase in scattering from 40% to 85% RH, fRH = 1.7 ± 0.2), while coarse-mode dust was found to have very low absorption (ω = 0.96 ± 0.01) and to be almost nonhygroscopic (fRH = 1.1 ± 0.1). These and other optical properties are intended to serve as constraints on optical models of the Asian aerosol for the purpose of satellite retrievals and calculations of direct radiative effects.

Measurements of aerosol composition were made with an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) on board the NSF/NCAR C-130 aircraft as part of the Intercontinental Chemical Transport Experiment Phase B (INTEX-B) field campaign over the Eastern Pacific Ocean. The HR-ToF-AMS measurements of non-refractory submicron aerosol mass are shown to compare well with other aerosol instrumentation in the INTEX-B field study. Two case studies are described for pollution layers transported across the Pacific from the Asian continent, intercepted 3–4 days and 7–10 days downwind of Asia, respectively. Aerosol chemistry is shown to be a robust tracer for air masses originating in Asia, specifically the presence of sulfate dominated aerosol is a distinguishing feature of Asian pollution layers that have been transported to the Eastern Pacific. We examine the time scales of processing for sulfate and organic aerosol in the atmosphere and show that our observations confirm a conceptual model for transpacific transport from Asia proposed by Brock et al. (2004). Our observations of both sulfate and organic aerosol in aged Asian pollution layers are consistent with fast formation near the Asian continent, followed by washout during lofting and subsequent transformation during transport across the Pacific. Our observations are the first atmospheric measurements to indicate that although secondary organic aerosol (SOA) formation from pollution happens on the timescale of one day, the oxidation of organic aerosol continues at longer timescales in the atmosphere. Comparisons with chemical transport models of data from the entire campaign reveal an under-prediction of organic aerosol mass in the MOZART model, but much smaller discrepancies with the GEOS-Chem model than found in previous studies over the Western Pacific. No evidence is found to support a previous hypothesis for significant secondary organic aerosol formation in the free troposphere.

In-situ airborne measurements of trace gases, aerosol size distributions, chemistry and optical properties were conducted over Mexico and the Eastern North Pacific during MILAGRO and INTEX-B. Heterogeneous reactions between secondary aerosol precursor gases and mineral dust lead to sequestration of sulfur, nitrogen and chlorine in the supermicrometer particulate size range. Simultaneous measurements of aerosol size distributions and weak-acid soluble calcium result in an estimate of 11 wt% of CaCO3 for Asian dust. During transport across the North Pacific, ~5–30% of the CaCO3 is converted to CaSO4 or Ca(NO3)2 with an additional ~4% consumed through reactions with HCl. The 1996 to 2008 record from the Mauna Loa Observatory confirm these findings, indicating that, on average, 19% of the CaCO3 has reacted to form CaSO4 and 7% has reacted to form Ca(NO3)2 and ~2% has reacted with HCl. In the nitrogen-oxide rich boundary layer near Mexico City up to 30% of the CaCO3 has reacted to form Ca(NO3)2 while an additional 8% has reacted with HCl. These heterogeneous reactions can result in a ~3% increase in dust solubility which has an insignificant effect on their optical properties compared to their variability in-situ. However, competition between supermicrometer dust and submicrometer primary aerosol for condensing secondary aerosol species led to a 25% smaller number median diameter for the accumulation mode aerosol. A 10–25% reduction of accumulation mode number median diameter results in a 30–70% reduction in submicrometer light scattering at relative humidities in the 80–95% range. At 80% RH submicrometer light scattering is only reduced ~3% due to a higher mass fraction of hydrophobic refractory components in the dust-affected accumulation mode aerosol. Thus reducing the geometric mean diameter of the submicrometer aerosol has a much larger effect on aerosol optical properties than changes to the hygroscopic:hydrophobic mass fractions of the accumulation mode aerosol. In the presence of dust, nitric acid concentrations are reduced to y as a fraction of total nitrogen (NOy plus particulate nitrate), is reduced from >85% to 60–80% in the presence of dust. These observations support previous model studies which predict irreversible sequestration of reactive nitrogen species through heterogeneous reactions with mineral dust during long-range transport.