.[1] The Aerosol Radiative Forcing in East Asia (A-FORCE) aircraft campaign was conducted over East Asia in March-April 2009. During the A-FORCE campaign, 120 vertical profiles of black carbon (BC) and carbon monoxide (CO) were obtained in the planetary boundary layer (PBL) and the free troposphere. This study examines the wet removal of BC in Asian outflow using the A-FORCE data. The concentrations of BC and CO were greatly enhanced in air parcels sampled at 3-6 km in altitude over the Yellow Sea on 30 March 2009, associated with upward transport due to a cyclone with modest amounts of precipitation over northern China. In contrast, high CO concentrations without substantial enhancements of BC concentrations were observed in air parcels sampled at 5-6 km over the East China Sea on 23 April 2009, caused by uplifting due to cumulus convection with large amounts of precipitation over central China. The transport efficiency of BC (TE BC , namely the fraction of BC particles not removed during transport) in air parcels sampled above 2 km during the entire A-FORCE period decreased primarily with the increase in the precipitation amount that air parcels experienced during vertical transport, although their correlation was modest (r 2 = 0.43). TE BC also depended on the altitude to which air parcels were transported from the PBL and the latitude where they were uplifted locally over source regions. The median values of TE BC for air parcels originating from northern China (north of 33°N) and sampled at 2-4 km and 4-9 km levels were 86% and 49%, respectively, during the A-FORCE period. These median values were systematically greater than the corresponding median values (69% and 32%, respectively) for air parcels originating from southern China (south of 33°N). Use of the A-FORCE data set will contribute to the reduction of large uncertainties in wet removal process of BC in global-and regional-scale models.

[1] The Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006) were mainly focused on the influence of the regional aerosol on the air pollution in Beijing. The urban aerosol was characterized in detail. The particle size distributions were also compared to those measured at a regional site (Yufa) approximately 50 km south of the urban site at Peking University (PKU). At PKU, total particle number and volume concentrations were (1.8 ± 0.8) Â 10 4 cm À3 and 83.5 ± 57.9 mm 3 cm À3 , respectively. Days in three consecutive summers of 2004, 2005, and 2006 were classified as polluted days with PM 10 over 150 mg m À3 and nonpolluted days with lower PM 10 . On nonpolluted days, particle number size distributions showed a maximum at about 60 nm with Aitken mode particles dominating number concentration. On polluted days, the contribution of accumulation mode particles increased, shifting the maximum of the number size distribution to over 80 nm. On polluted days with stagnant meteorological conditions, secondary aerosol dominated, with SO 4 2À , NO 3 À , and NH 4 + accounting for over 60% of accumulation mode particle mass. Particle number size distributions at both sites were similar. Number and volume concentrations of total particles at Yufa were 6% and 12% lower, respectively; those of accumulation mode particles were 2% and 15% lower. This means that air pollution in Beijing is mainly a regional problem. The regional accumulation mode particles are a metric for assessing the air quality since they influence most the visibility and total mass concentration. Their number and volume concentrations on polluted days were 5 Â 10 3 cm À3 and 30 mm 3 cm À3 , respectively. Five new particle formation (NPF) events with continuous smooth growth were observed at both PKU and Yufa during CAREBeijing-2006. These NPF events are regional or semiregional. Growth rates at PKU ranged from 1.2 to 5.6 nm h À1 , and formation rates ranged from 1.

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[1] To investigate the distributions and sources of water-soluble organic acids in the Mongolian atmosphere, aerosol samples (PM 2.5 , n = 34) were collected at an urban site (47.92°N, 106.90°E, ∼1300 m above sea level) in Ulaanbaatar, the capital of Mongolia, during the cold winter. The samples were analyzed for water-soluble dicarboxylic acids (C 2 -C 12 ) and related compounds (ketocarboxylic acids and a-dicarbonyls), as well as organic carbon (OC), elemental carbon, water-soluble OC, and inorganic ions. Distributions of dicarboxylic acids and related compounds were characterized by a predominance of terephthalic acid (tPh; 130 ± 51 ng m −3 , 19% of total detected organic acids) followed by oxalic (107 ± 28 ng m −3 , 15%), succinic (63 ± 20 ng m −3 , 9%), glyoxylic (55 ± 18 ng m −3 , 8%), and phthalic (54 ± 27 ng m −3 , 8%) acids. Predominance of terephthalic acid, which has not been reported previously in atmospheric aerosols, was mainly due to uncontrolled burning of plastic bottles and bags in home stoves for heating and waste incineration during the cold winter. This study demonstrated that most of the air pollutants were directly emitted from local sources such as heat and power plants, home stoves, and automobiles. Development of an inversion layer (<700 m above ground level) over the basin of Ulaanbaatar accelerated the accumulation of pollutants, causing severe haze episodes during the winter season.

[1] In order to investigate the optical properties of atmospheric aerosol in the urban area of Beijing, in situ and remote measurements of particulate pollutants were conducted at an urban site ( , respectively. Average mass scattering efficiency of PM 10 and PM 2.5 particle were found to be 2.5 ± 1.1 and 3.4 ± 1.2 m 2 g À1 , respectively. Average single scattering albedo (SSA) of dry PM 10 was characterized to be 0.82 ± 0.09. It was found that SSA decreased to lower values of $0.75 during the relatively clean condition while it increased up to $0.86 during polluted condition mainly owing to the increases of ammonium sulfate, ammonium nitrate, and organic mass by carbon's contributions to PM mass concentrations. Pollution episodes in Beijing were strongly related to wind speed and wind direction. Stagnant weather conditions with southerly wind and low wind speed accelerated the accumulation of the pollutants in Beijing, which led to severe haze. It has been found that high PM 2.5 /AOT (aerosol optical thickness) ratio of 228.2 mg m À3 was observed when air mass was transported from western or northern China while significantly lower PM 2.5 /AOT of 107.6 mg m À3 was observed when it was affected mostly by local air pollutants in Beijing.

Abstract. In situ measurements of the mass concentration of black carbon (BC) and mixing ratios of carbon monoxide (CO) and carbon dioxide (CO 2 ) were made at Guangzhou, an urban measurement site in the Pearl River Delta (PRD), China, in July 2006. The average ± standard deviation (SD) concentrations of BC, CO, and CO 2 were 4.7±2.3 µgC m −3 , 798±459 ppbv, and 400±13 ppmv, respectively. The trends of these species were mainly controlled by synoptic-scale changes in meteorology during the campaign. Based on back trajectories, data are analyzed separately for two different air mass types representing northerly and southerly flows. The northerly air masses, which constituted ∼25% of the campaign, originated mostly in the PRD and hence represent observations on regional scales. On the other hand, during southerly flow (∼75%), the measurements were influenced by dilution due to cleaner marine air. The diurnal patterns of BC, CO, and CO 2 exhibited peak concentrations during the morning and evening hours coinciding with rush-hour traffic. The ratios of OC/BC were lower during the morning hour peaks in the concentrations of primary pollutants due to their fresh emissions mainly from vehicular traffic in Guangzhou. The diurnal variations of BC observed in southerly airCorrespondence to: Y. Kondo (y.kondo@atmos.rcast.u-tokyo.ac.jp) masses tended to follow the traffic patterns of heavy-duty vehicles (HDV) in Guangzhou, while the roles of other sources need to be investigated. The slopes of BC/ CO, BC/ CO 2 , and CO/ CO 2 observed during northerly flows were 0.0045 µgC m −3 /ppbv, 0.13 µgC m −3 /ppmv, and 49.4 ppbv/ppmv, respectively, agreeing reasonably with their respective emission ratios derived from regional emission inventories.

deployed instrumented aircraft and ground-based measurements to elucidate causes of poor air quality related to high ozone and aerosol concentrations in South Korea. This work synthesizes data pertaining to aerosols (specifically, particulate matter with aerodynamic diameters <2.5 micrometers, PM 2.5) and conditions leading to violations of South Korean air quality standards (24-hr mean PM 2.5 < 35 µg m-3). PM 2.5 variability from AirKorea monitors across South Korea is evaluated. Detailed data from the Seoul vicinity are used to interpret factors that contribute to elevated PM 2.5. The interplay between meteorology and surface aerosols, contrasting synoptic-scale behavior vs. local influences, is presented. Transboundary transport from upwind sources, vertical mixing and containment of aerosols, and local production of secondary aerosols are discussed. Two meteorological periods are probed for drivers of elevated PM 2.5. Clear, dry conditions, with limited transport (Stagnant period), promoted photochemical production of secondary organic aerosol from locally emitted precursors. Cloudy humid conditions fostered rapid heterogeneous secondary inorganic aerosol production from local and transported emissions (Transport/Haze period), likely driven by a positive feedback mechanism where water uptake by aerosols increased gas-to-particle partitioning that increased water uptake. Further, clouds reduced solar insolation, suppressing mixing, exacerbating PM 2.5 accumulation in a shallow boundary layer. The combination of factors contributing to enhanced PM 2.5 is challenging to model, complicating quantification of contributions to PM 2.5 from local versus upwind precursors and production. We recommend co-locating additional continuous measurements at a few AirKorea sites across South Korea to help resolve this and other outstanding questions: carbon monoxide/carbon dioxide (transboundary transport tracer), boundary layer height (surface PM 2.5 mixing depth), and aerosol composition with aerosol liquid water (meteorologically-dependent secondary production). These data would aid future research to refine emissions targets to further improve South Korean PM 2.5 air quality.