Organic aerosol (OA) data acquired by the Aerosol Mass Spectrometer (AMS) in 37 field campaigns were deconvolved into hydrocarbon‐like OA (HOA) and several types of oxygenated OA (OOA) components. HOA has been linked to primary combustion emissions (mainly from fossil fuel) and other primary sources such as meat cooking. OOA is ubiquitous in various atmospheric environments, on average accounting for 64%, 83% and 95% of the total OA in urban, urban downwind, and rural/remote sites, respectively. A case study analysis of a rural site shows that the OOA concentration is much greater than the advected HOA, indicating that HOA oxidation is not an important source of OOA, and that OOA increases are mainly due to SOA. Most global models lack an explicit representation of SOA which may lead to significant biases in the magnitude, spatial and temporal distributions of OA, and in aerosol hygroscopic properties.

Abstract. We evaluate black carbon (BC) model predictions from the AeroCom model intercomparison project by considering the diversity among year 2000 model simulations and comparing model predictions with available measurements. These model-measurement intercomparisons include BC surface and aircraft concentrations, aerosol absorption optical depth (AAOD) retrievals from AERONET and Ozone Monitoring Instrument (OMI) and BC column estimations based on AERONET. In regions other than Asia, most models are biased high compared to surface concentration measurements. However compared with (column) AAOD or BC burden retreivals, the models are generally biased low. The average ratio of model to retrieved AAOD is less than 0.7 in South American and 0.6 in African biomass burning regions; both of these regions lack surface concentration measurements. In Asia the average model to observed ratio is 0.7 for AAOD and 0.5 for BC surface concentrations. Compared with aircraft measurements over the Americas at latitudes between 0 and 50N, the average model is a factor of 8 larger than observed, and most models exceed the measured BC standard deviation in the mid to upper troposphere. At higher latitudes the average model to aircraft BC ratio is 0.4 and models underestimate the observed BC loading in the lower and middle troposphere associated with springtime Arctic haze. Low model bias for AAOD but overestimation of surface and upper atmospheric BC concentrations at lower latitudes suggests that most models are underestimating BC absorption and should improve estimates for refractive index, particle size, and optical effects of BC coating. Retrieval uncertainties and/or differences with model diagnostic treatment may also contribute to the model-measurement disparity. Largest AeroCom model diversity occurred in northern Eurasia and the remote Arctic, regions influenced by anthropogenic sources. Changing emissions, aging, removal, or optical properties within a single model generated a smaller change in model predictions than the range represented by the full set of AeroCom models. Upper tropospheric concentrations of BC mass from the aircraft measurements are suggested to provide a unique new benchmark to test scavenging and vertical dispersion of BC in global models.

[1] Reliable assessment of the impact of aerosols emitted from boreal forest fires on the Arctic climate necessitates improved understanding of emissions and the microphysical properties of carbonaceous (black carbon (BC) and organic aerosols (OA)) and inorganic aerosols. The size distributions of BC were measured by an SP2 based on the laser-induced incandescence technique on board the DC-8 aircraft during the NASA ARCTAS campaign. Aircraft sampling was made in fresh plumes strongly impacted by wildfires in North America (Canada and California) in summer 2008 and in those transported from Asia (Siberia in Russia and Kazakhstan) in spring 2008. We extracted biomass burning plumes using particle and tracer (CO, CH 3 CN, and CH 2 Cl 2 ) data. OA constituted the dominant fraction of aerosols mass in the submicron range. The large majority of the emitted particles did not contain BC. We related the combustion phase of the fire as represented by the modified combustion efficiency (MCE) to the emission ratios between BC and other species. In particular, we derived the average emission ratios of BC/CO = 2.3 ± 2.2 and 8.5 ± 5.4 ng m −3 /ppbv for BB in North America and Asia, respectively. The difference in the BC/CO emission ratios is likely due to the difference in MCE. The count median diameters and geometric standard deviations of the lognormal size distribution of BC in the BB plumes were 136-141 nm and 1.32-1.36, respectively, and depended little on MCE. These BC particles were thickly coated, with shell/core ratios of 1.3-1.6. These parameters can be used directly for improving model estimates of the impact of BB in the Arctic.

Abstract. We evaluate black carbon (BC) model predictions from the AeroCom model intercomparison project by considering the diversity among year 2000 model simulations and comparing model predictions with available measurements. These model-measurement intercomparisons include BC surface and aircraft concentrations, aerosol absorption optical depth (AAOD) from AERONET and Ozone Monitoring Instrument (OMI) retrievals and BC column estimations based on AERONET. In regions other than Asia, most models are biased high compared to surface concentration measurements. However compared with (column) AAOD or BC burden retreivals, the models are generally biased low. The average ratio of model to retrieved AAOD is less than 0.7 in South American and 0.6 in African biomass burning regions; both of these regions lack surface concentration measurements. In Asia the average model to observed ratio is 0.6 for AAOD and 0.5 for BC surface concentrations. Compared with aircraft measurements over the Americas at latitudes between 0 and 50 N, the average model is a factor of 10 larger than observed, and most models exceed the measured BC standard deviation in the mid to upper troposphere. At higher latitudes the average model to aircraft BC is 0.6 and underestimates the observed BC loading in the lower and middle troposphere associated with springtime Arctic haze. Low model bias for AAOD but overestimation of surface and upper atmospheric BC concentrations at lower latitudes suggests that most models are underestimating BC absorption and should improve estimates for refractive index, particle size, and optical effects of BC coating. Retrieval uncertainties and/or differences with model diagnostic treatment may also contribute to the model-measurement disparity. Largest AeroCom model diversity occurred in northern Eurasia and the remote Arctic, regions influenced by anthropogenic sources. Changing emissions, aging, removal, or optical properties within a single model generated a smaller change in model predictions than the range represented by the full set of AeroCom models. Upper tropospheric concentrations of BC mass from the aircraft measurements are suggested to provide a unique new benchmark to test scavenging and vertical dispersion of BC in global models.

[1] We used laser-induced fluorescence to measure the concentrations of OH and HO 2 radicals in central Tokyo during two intensive campaigns (IMPACT IVand IMPACT L) in January-February and July-August 2004. The estimated detection limit for the 10-min data was 1.3 Â 10 5 cm À3 for the nighttime and 5.2 Â 10 5 cm À3 for the daytime. The median values of the daytime peak concentrations of HO 2 were 1.1 and 5.7 pptv for the winter and summer periods, respectively, while the values for OH were 1.5 Â 10 6 and 6.3 Â 10 6 cm À3 . High HO 2 mixing ratios (>50 pptv) were observed on a day in summer when O 3 mixing ratios exceeded 100 ppbv. The average nighttime concentrations of HO 2 were 0.7 and 2.6 pptv for the winter and summer periods, respectively, while the values for OH were 1.8 Â 10 5 and 3.7 Â 10 5 cm À3 . A photochemical box model constrained by ancillary observations was able to reproduce daytime OH concentrations reasonably well for both periods, although daytime HO 2 concentrations were underestimated in winter and overestimated in summer. Increasing the wintertime hydrocarbon concentrations in the model led to an increase in daytime HO 2 concentrations, thereby showing better agreement with observations; however, the model continued to underestimate HO 2 concentrations at high NO mixing ratios. This underestimate was most pronounced in the mornings of both periods and during the daytime in winter. We studied processes that are capable of explaining this discrepancy, including unknown reactions of HNO 4 or an unidentified HO x source that is linearly scalable to the NO mixing ratio. The important processes in terms of producing radicals were the olefin + O 3 reactions in the nighttime of both periods and during the daytime in winter, the photolysis of carbonyls in the daytime for both periods, and the photolysis of HONO during the daytime in winter (using measured HONO concentrations) and during mornings in summer (using estimated HONO concentrations).

[1] Submicron organic aerosol was measured simultaneously with an Aerodyne aerosol mass spectrometer (AMS) and a particle-into-liquid sampler (PILS) capable of measuring water-soluble organic carbon (WSOC) during the winter and summer of 2004 in Tokyo. Both techniques are being used to investigate the formation of secondary organic aerosol (SOA), and the combined data sets provide unique insights. In summer, about 80% (40-65%) of organic aerosols were oxygenated when scaled by total (carbon) mass concentration, due to high photochemical activity, leading to the active formation of SOA. In winter the fraction of oxygenated organic aerosol is reduced to 39% (total mass base) and 23% (carbon mass base). Previous AMS studies have shown that signals at m/z 44 of the AMS mass spectra of ambient aerosols are dominated by COO + , which typically originates from oxygenated organic aerosols (OOA). The signals at m/z 44 and the derived OOA mass concentrations were highly correlated with WSOC (r 2 = 0.78-0.91) throughout these seasons, indicating that OOA and WSOC were very similar in their chemical characteristics. Approximately 88 ± 29% of OOA was found to be water soluble on the basis of the comparison of the WSOC concentrations with those of oxygenated organic carbon (OOC) derived from the AMS data.

In this study, we show that black carbon (BC) mass concentrations measured by different techniques are consistent and traceable. First, we present the volatilities of 13 organic compounds passed through a heated inlet. These data were used to quantify the interference of organic aerosols on the BC measurement techniques. The masses of the refractory particles that incandesce (m * ref ) were used to calibrate BC mass measured by a single-particle soot photometer (SP2), which uses laser-induced incandescence. This calibration was influenced little by refractory organics and agreed well with that of fullerene soot, which indicates the consistency of the standards. We estimated the interference of pyrolyzed refractory organics on the BC measured with a filter-based absorption photometer continuous soot monitoring system (COSMOS) with a heated inlet to be small in Asia. This was also confirmed by the stable mass absorption cross section (MAC) obtained by the high correlations between BC mass concentrations measured by COSMOS (M COSMOS ) and those measured by the thermal-optical transmittance method (M TOT ) (Kondo et al. 2009). M COSMOS was also compared with total BC mass concentrations measured with an SP2 (M SP2 ) in Tokyo in 2009. M COSMOS and M SP2 were highly correlated (r 2 = 0.97) and agreed to within about 10% on average. These results demonstrate that M SP2 , M COSMOS , and M TOT were nearly identical. Use of the masses of incandescing refractory BC

Abstract. We performed measurements of nitrous acid (HONO) during the PRIDE-PRD2006 campaign in the Pearl River Delta region 60 km north of Guangzhou, China, for 4 weeks in June 2006. HONO was measured by a LOPAP in-situ instrument which was setup in one of the campaign supersites along with a variety of instruments measuring hydroxyl radicals, trace gases, aerosols, and meteorological parameters. Maximum diurnal HONO mixing ratios of 1-5 ppb were observed during the nights. We found that the nighttime build-up of HONO can be attributed to the heterogeneous NO 2 to HONO conversion on ground surfaces and the OH + NO reaction. In addition to elevated nighttime mixing ratios, measured noontime values of ≈200 ppt indicate the existence of a daytime source higher than the OH + NO→HONO reaction. Using the simultaneously recorded OH, NO, and HONO photolysis frequency, a daytime additional source strength of HONO (P M ) was calculated to be 0.77 ppb h −1 on average. This value compares well to previous measurements in other environments. Our analysis of P M provides evidence that the photolysis of HNO 3 adsorbed on ground surfaces contributes to the HONO formation.