Atmospheric Environment (v.78, #C)

An overview of regional experiments on biomass burning aerosols and related pollutants in Southeast Asia: From BASE-ASIA and the Dongsha Experiment to 7-SEAS by Neng-Huei Lin; Si-Chee Tsay; Hal B. Maring; Ming-Cheng Yen; Guey-Rong Sheu; Sheng-Hsiang Wang; Kai Hsien Chi; Ming-Tung Chuang; Chang-Feng Ou-Yang; Joshua S. Fu; Jeffrey S. Reid; Chung-Te Lee; Lin-Chi Wang; Jia-Lin Wang; Christina N. Hsu; Andrew M. Sayer; Brent N. Holben; Yu-Chi Chu; Xuan Anh Nguyen; Khajornsak Sopajaree; Shui-Jen Chen; Man-Ting Cheng; Ben-Jei Tsuang; Chuen-Jinn Tsai; Chi-Ming Peng; Russell C. Schnell; Tom Conway; Chang-Tang Chang; Kuen-Song Lin; Ying I. Tsai; Wen-Jhy Lee; Shuenn-Chin Chang; Jyh-Jian Liu; Wei-Li Chiang; Shih-Jen Huang; Tang-Huang Lin; Gin-Rong Liu (1-19).
By modulating the Earth-atmosphere energy, hydrological and biogeochemical cycles, and affecting regional-to-global weather and climate, biomass burning is recognized as one of the major factors affecting the global carbon cycle. However, few comprehensive and wide-ranging experiments have been conducted to characterize biomass-burning pollutants in Southeast Asia (SEA) or assess their regional impact on meteorology, the hydrological cycle, the radiative budget, or climate change. Recently, BASE-ASIA (Biomass-burning Aerosols in South-East Asia: Smoke Impact Assessment) and the 7-SEAS (7-South-East Asian Studies)/Dongsha Experiment were conducted during the spring seasons of 2006 and 2010 in northern SEA, respectively, to characterize the chemical, physical, and radiative properties of biomass-burning emissions near the source regions, and assess their effects. This paper provides an overview of results from these two campaigns and related studies collected in this special issue, entitled “Observation, modeling and impact studies of biomass burning and pollution in the SE Asian Environment”. This volume includes 28 papers, which provide a synopsis of the experiments, regional weather/climate, chemical characterization of biomass-burning aerosols and related pollutants in source and sink regions, the spatial distribution of air toxics (atmospheric mercury and dioxins) in source and remote areas, a characterization of aerosol physical, optical, and radiative properties, as well as modeling and impact studies. These studies, taken together, provide the first relatively complete dataset of aerosol chemistry and physical observations conducted in the source/sink region in the northern SEA, with particular emphasis on the marine boundary layer and lower free troposphere (LFT). The data, analysis and modeling included in these papers advance our present knowledge of source characterization of biomass-burning pollutants near the source regions as well as the physical and chemical processes along transport pathways. In addition, we raise key questions to be addressed by a coming deployment during springtime 2013 in northern SEA, named 7-SEAS/BASELInE (Biomass-burning Aerosols & Stratocumulus Environment: Lifecycles and Interactions Experiment). This campaign will include a synergistic approach for further exploring many key atmospheric processes (e.g., complex aerosol–cloud interactions) and impacts of biomass burning on the surface–atmosphere energy budgets during the lifecycles of biomass-burning emissions.Display Omitted
Keywords: Biomass burning; Aerosol; Air toxics; Southeast Asia; 7-SEAS; BASE-ASIA; Dongsha Experiment;

From BASE-ASIA toward 7-SEAS: A satellite-surface perspective of boreal spring biomass-burning aerosols and clouds in Southeast Asia by Si-Chee Tsay; N. Christina Hsu; William K.-M. Lau; Can Li; Philip M. Gabriel; Qiang Ji; Brent N. Holben; E. Judd Welton; Anh X. Nguyen; Serm Janjai; Neng-Huei Lin; Jeffrey S. Reid; Jariya Boonjawat; Steven G. Howell; Barry J. Huebert; Joshua S. Fu; Richard A. Hansell; Andrew M. Sayer; Ritesh Gautam; Sheng-Hsiang Wang; Colby S. Goodloe; Laddawan R. Miko; Peter K. Shu; Adrian M. Loftus; Jingfeng Huang; Jin Young Kim; Myeong-Jae Jeong; Peter Pantina (20-34).
► Multi-year, international efforts for studying aerosol and climate impacts across Southeast Asia. ► Aerosol and cloud properties measured from both ground- and satellite-based platforms. ► Investigation of aerosol–cloud interactions and planning for future experiments.
Keywords: Biomass-burning; Aerosol; Cloud; Southeast Asia; BASE-ASIA; 7-SEAS;

Climate and weather characteristics in association with the active fires in northern Southeast Asia and spring air pollution in Taiwan during 2010 7-SEAS/Dongsha Experiment by Ming-Cheng Yen; Chi-Ming Peng; Tsing-Chang Chen; Ching-Sen Chen; Neng-Huei Lin; Ren-Yow Tzeng; Yung-An Lee; Cheng-Chih Lin (35-50).
Climatologically, the East Asian high merges with the westward expansion of the northwestern Pacific subtropical high in March. The local East–West cell/circulation is enhanced by a well-organized convergent center that forms over Indochina at 925 h Pa in March. This allows the emitted air pollutants from the biomass burning to be uplifted to the free troposphere and immediately transported downwind to the east. Using the data collected from the 2010 7-SEAS/Dongsha Experiment, six cases of long-range transport events involving air pollutants during March–April were identified at the Hengchun air quality monitoring station in southern Taiwan. These events were related to active burning phases over Indochina Peninsula. The air pollutants produced by these events were transported to Taiwan after a 2–3 day journey. A composite analysis for these identified six cases showed that the boundary layer of the southwesterly flow confluence coupled with a well-organized convergent center located over a thermal low under clear skies over the Indochina Peninsula may induce a distinct ascending motion to form the upward branch of the transient local East–West cell/circulation during the burning phase. This inferred upward motion together with the strong thermal buoyancy created by the active biomass burnings could carry the air pollutants to the lower free troposphere where they would effectively be conveyed downwind along the westerly flow above 850 h Pa level. The air pollutants were brought down to the surface by downward branch of the transient local East–West cell/circulation, which was induced by the subsidence of a cold surge anticyclone. Using continuous point sources, the six identified cases were simulated with the Hybrid Single-Particle Lagrangian-Integrated Trajectory (HYSPLIT) particle dispersion forward model to confirm our supposition regarding the mechanism for the long-range transport of Southeast Asian biomass burning pollutants that has a significant impact on the surface air quality of the downstream areas, particularly in Taiwan.► Southeast Asian biomass burning pollutants long-range transport identified on Taiwan surface. ► The East Asian high merges with northwestern Pacific subtropical high east of Taiwan. ► Local East–West cell/circulation helps air pollutants uplift and downwind transport. ► Clear sky surface thermal low over Indochina may induce a distinct upward motion. ► Forward particle dispersion simulations confirm the long-range transport speculation.
Keywords: Biomass burning; Cold surge; Divergent circulation; Long-range transport; Northwestern Pacific subtropical high; Local East–West circulation;

Characterization of aerosols over the Indochina peninsula from satellite-surface observations during biomass burning pre-monsoon season by Ritesh Gautam; N. Christina Hsu; Thomas F. Eck; Brent N. Holben; Serm Janjai; Treenuch Jantarach; Si-Chee Tsay; William K. Lau (51-59).
This paper presents characterization of aerosols over the Indochina peninsular regions of Southeast Asia during pre-monsoon season from satellite and ground-based radiometric observations. Our analysis focuses on the seasonal peak period in aerosol loading and biomass burning, prior to the onset of the Asian summer monsoon, as observed in the inter-annual variations of Aerosol Optical Depth (AOD) and fire count data from MODIS. Multi-year (2007–2011) analysis of spaceborne lidar measurements, from CALIOP, indicates presence of aerosols mostly within boundary layer, however extending to elevated altitudes to ∼4 km over northern regions of Indochina, encompassing Myanmar, northern Thailand and southern China. In addition, a strong gradient in aerosol loading and vertical distribution is observed from the relatively clean equatorial conditions to heavy smoke-laden northern regions (greater aerosol extinction and smaller depolarization ratio). Based on column-integrated ground-based measurements from four AERONET locations distributed over Thailand, the regional aerosol loading is found to be significantly absorbing with spectral single scattering albedo (SSA) below 0.91 ± 0.02 in the 440–1020 nm range, with lowest seasonal mean SSA (most absorbing aerosol) over the northern location of Chiang Mai (SSA ∼ 0.85) during pre-monsoon season. The smoke-laden aerosol loading is found to exhibit a significant diurnal pattern with higher AOD departures during early morning observations relative to late afternoon conditions (peak difference of more than 15% amplitude). Finally, satellite-based aerosol radiative impact is assessed using CERES shortwave Top-of-Atmosphere flux, in conjunction with MODIS AOD. Overall, a consistency in the aerosol-induced solar absorption characteristic is found among selected regions from ground-based sunphotometer-derived spectral SSA retrievals and satellite-based radiative forcing analysis.► Characterization of aerosols over Indochina from satellite and surface observations. ► Multi-year analysis of aerosol vertical distribution is presented from CALIOP data. ► Regional aerosol loading is found to be significantly absorbing from AERONET data. ► The smoke-laden aerosol loading is found to exhibit a significant diurnal pattern. ► Satellite-based aerosol radiative impact is assessed using CERES data.
Keywords: Aerosol; Remote sensing; Southeast Asia; Biomass burning;

Characteristics and composition of atmospheric aerosols in Phimai, central Thailand during BASE-ASIA by Can Li; Si-Chee Tsay; N. Christina Hsu; Jin Young Kim; Steven G. Howell; Barry J. Huebert; Qiang Ji; Myeong-Jae Jeong; Sheng-Hsiang Wang; Richard A. Hansell; Shaun W. Bell (60-71).
Comprehensive measurements of atmospheric aerosols were made in Phimai, central Thailand (15.183°N, 102.565°E, elevation: 206 m) during the BASE-ASIA field experiment from late February to early May in 2006. The observed aerosol loading was sizable for this rural site (mean aerosol scattering: 108 ± 64 Mm−1; absorption: 15 ± 8 Mm−1; PM10 concentration: 33 ± 17 μg m−3), and dominated by submicron particles. Major aerosol compounds included carbonaceous (OC: 9.5 ± 3.6 μg m−3; EC: 2.0 ± 2.3 μg m−3) and secondary species (SO4 2−: 6.4 ± 3.7 μg m−3, NH4 +: 2.2 ± 1.3 μg m−3). While the site was seldom under the direct influence of large forest fires to its north, agricultural fires were ubiquitous during the experiment, as suggested by the substantial concentration of K+ (0.56 ± 0.33 μg m−3). Besides biomass burning, aerosols in Phimai during the experiment were also strongly influenced by industrial and vehicular emissions from the Bangkok metropolitan region and long-range transport from southern China. High humidity played an important role in determining the aerosol composition and properties in the region. Sulfate was primarily formed via aqueous phase reactions, and hygroscopic growth could enhance the aerosol light scattering by up to 60%, at the typical morning RH level of 85%. The aerosol single scattering albedo demonstrated distinct diurnal variation, ranging from 0.86 ± 0.04 in the evening to 0.92 ± 0.02 in the morning. This experiment marks the first time such comprehensive characterization of aerosols was made for rural central Thailand. Our results indicate that aerosol pollution has developed into a regional problem for northern Indochina, and may become more severe as the region's population and economy continue to grow.► First detailed, comprehensive aerosol measurements in rural central Thailand. ► Industrial emissions, long-range transport and agricultural fires all influence aerosol loading. ► Effects of aerosol hygroscopic growth on light extinction investigated.
Keywords: Southeast Asia; Aerosols; Chemical composition; Microphysical properties; Optical properties;

Characterization of aerosol chemical properties from near-source biomass burning in the northern Indochina during 7-SEAS/Dongsha experiment by Ming-Tung Chuang; Charles C.-K. Chou; Khajornsak Sopajaree; Neng-Huei Lin; Jia-Lin Wang; Guey-Rong Sheu; You-Jia Chang; Chung-Te Lee (72-81).
Biomass burning (BB) in Indochina produces a great amount of aerosols, but related information on this phenomenon is scarce. In the present study, aerosol samples were collected from Suthep Mountain (98° 53′E, 18° 48′N, 1396 m) in Chiangmai, Northern Indochina, in March and April 2010. To our knowledge, this study is the first to reveal the chemical characteristics of BB aerosol near the burning sources in Indochina. The composition analyzed included water-soluble ions, carbonaceous fractions obtained using the thermal optical reflectance method, low-molecular-weight dicarboxylates, anhydrosugars, and water-soluble organic carbon (WSOC). Enriched tracers from the collected aerosols, such as potassium ion (K+) and levoglucosan, confirmed that the samples were influenced by BB activity. The percentage of K+ in PM2.5 (2.51% ± 0.31%) in the present study is higher than that in other studies. The analysis also showed that directly emitted organic carbon (OC) is the most abundant component in the collected particles. The percentage of WSOC in OC in the present study is greater than that in laboratory experiments. Moreover, the char-EC to soot-EC ratio (defined as the ratio of the subtraction of pyrolized OC from the measured EC1, EC1-OP, over the sum of EC2 and EC3) of 9.4 ± 3.8 in PM2.5 is similar to the value of BB in the literature. Using the recognized BB aerosol tracers K+ and levoglucosan, the present study inferred that PM2.5 EC1-OP and OC3 are also good BB tracers near sources. The collected BB aerosols may have been contributed by the smoldering state of softwood burning.► The first aerosol characterization for near-source biomass burning in Indochina. ► Organic carbon is the most abundant aerosol component. ► The percentage of K+ in PM2.5 is higher than in other ambient studies. ► PM2.5 K+, levoglucosan, EC1-OP, and OC3 are good BB tracers near sources. ► The collected aerosol was inferred from the smoldering state of softwood burning.
Keywords: Indochina; Aerosol source profile; Aerosol chemical composition; Biomass burning aerosol tracers;

Aerosol chemical properties and related pollutants measured in Dongsha Island in the northern South China Sea during 7-SEAS/Dongsha Experiment by Ming-Tung Chuang; Shuenn-Chin Chang; Neng-Huei Lin; Jia-Lin Wang; Guey-Rong Sheu; You-Jia Chang; Chung-Te Lee (82-92).
Aerosol observations were conducted at Dongsha Island in two batches from 19 to 23 March and 10 to 19 April 2010. Dongsha Island is located in a remote area over the northern South China Sea (SCS), distantly surrounded by southern China, Taiwan, the Philippines, and the Indochinese Peninsula. During the study period, the average PM10 and PM2.5 mass concentrations were 26.5 ± 19.4 and 12.6 ± 6.0 μg m−3, respectively. In particular, a daily PM10 concentration of 94.1 μg m−3 caused by a yellow-dust event originating from the Asian Continent was recorded on 21 March. Other than this event, the PM2.5 and PM10–2.5 daily levels were 7.1 ± 1.2 and 12.6 ± 5.0 μg m−3, respectively, on days without pollution from anthropogenic sources in the surrounding areas. Water-soluble ions (WSIs) were the predominant components that accounted for 58.7% ± 10.5% and 51.1% ± 7.2% of the PM10 and PM2.5 mass. The second most abundant component was carbonaceous content, which accounted for 9.5% ± 4.7% and 17.5% ± 5.3% of PM10 and PM2.5, respectively. SO 4 2 − was the most abundant PM2.5 WSI, whereas the Na+ and Cl pair was the most abundant PM10–2.5 WSI. Based on the U.S. IMPROVE protocol, the resolved carbonaceous fractions were mainly distributed in PM2.5 and influenced by coal combustion, mobile vehicles, and biomass burning. Most of the resolved WSIs in particles were in the liquid phase due to the humid environment around the northern SCS.► This study provides aerosol information in the northern South China Sea. ► The yellow-dust transport from the Asian Continent was observed. ► Ground PM2.5 level was about 7 μg m−3 in the pristine West Pacific.
Keywords: Aerosol chemical properties; South China Sea; Dongsha Island; 7-SEAS;

Source indicators of biomass burning associated with inorganic salts and carboxylates in dry season ambient aerosol in Chiang Mai Basin, Thailand by Ying I. Tsai; Khajornsak Sopajaree; Auranee Chotruksa; Hsin-Ching Wu; Su-Ching Kuo (93-104).
PM10 aerosol was collected between February and April 2010 at an urban site (CMU) and an industrial site (TOT) in Chiang Mai, Thailand, and characteristics and provenance of water-soluble inorganic species, carboxylates, anhydrosugars and sugar alcohols were investigated with particular reference to air quality, framed as episodic or non-episodic pollution. Sulfate, a product of secondary photochemical reactions, was the major inorganic salt in PM10, comprising 25.9% and 22.3% of inorganic species at CMU and TOT, respectively. Acetate was the most abundant monocarboxylate, followed by formate. Oxalate was the dominant dicarboxylate. A high acetate/formate mass ratio indicated that primary traffic-related and biomass-burning emissions contributed to Chiang Mai aerosols during episodic and non-episodic pollution. During episodic pollution carboxylate peaks indicated sourcing from photochemical reactions and/or directly from traffic-related and biomass burning processes and concentrations of specific biomarkers of biomass burning including water-soluble potassium, glutarate, oxalate and levoglucosan dramatically increased. Levoglucosan, the dominant anhydrosugar, was highly associated with water-soluble potassium (r = 0.75–0.79) and accounted for 93.4% and 93.7% of anhydrosugars at CMU and TOT, respectively, during episodic pollution. Moreover, levoglucosan during episodic pollution was 14.2–21.8 times non-episodic lows, showing clearly that emissions from biomass burning are the major cause of PM10 episodic pollution in Chiang Mai. Additionally, the average levoglucosan/mannosan mass ratio during episodic pollution was 14.1–14.9, higher than the 5.73–7.69 during non-episodic pollution, indicating that there was more hardwood burning during episodic pollution. Higher concentrations of glycerol and erythritol during episodic pollution further indicate that biomass burning activities released soil biota from forest and farmland soils.► PM10 pollution in Chiang Mai, Thailand, during biomass burning. ► Two sites and two types of pollution (episodic and non-episodic) compared. ► Carboxylates show traffic, photochemical and biomass sources in PM10 episodes. ► Levoglucosan highs indicate biomass burning major cause of PM10 episodic pollution. ► Levo/Manno ratio shows hardwood burning, particularly, leads to PM10 episodes.
Keywords: Chiang Mai; Biomarkers; Carboxylates; Levoglucosan; Sugar alcohols; Soil biota;

Intensive monitoring for PM mass and composition was conducted during December 2006–February 2007 at a mixed site in Hanoi, Vietnam. Fluctuations in levels of 24 h PM2.5 (26–143 μg m−3) and PM10 (37–165 μg m−3) were examined in relation to weather conditions and regional synoptic patterns. High 24 h PM levels were observed at low wind speeds when a stagnating ridge governed over Northern Vietnam. Diurnal variations of PM mass and composition, analyzed using 4 h-samples, reflected the influence of local emissions with peaks of PM mass and EC/OC observed during morning and evening rush hours. The 24 h EC and OC levels in PM2.5, 1.5–4.9 μg m−3 and 10–39 μg m−3, respectively, constituted about 90% of the total EC and OC in PM10. Ionic species ( SO 4 2 − , NO 3 − , NH 4 + , Cl and K+) were the major composition of PM2.5, whereas elements (Ca, Si, Al and Fe) were the major components in the coarse fraction (PM10 2.5). The reconstructed mass, explained 78 ± 11% of PM2.5 and 61 ± 11% of PM10 2.5, suggested significant contributions of secondary PM (OM, SO 4 2 − , NO 3 − and NH 4 + ) and combustion (biomass, diesel, etc.) to PM2.5. PMF model revealed 7 source factors of PM2.5: secondary mixed PM (40%), diesel traffic (10%), residential/commercial cooking (16%), secondary sulfate rich (16%), aged seasalt mixed (11%), industry/incinerator (6%), and construction/soil (1%). Contributions from local emission sources and the potential long-range transport were analyzed using the PM compositions and the diurnal variations in relation to local source activities, location of local sources, winds and air mass HYSPLIT trajectories. Major part of PM2.5 mass appeared to link to local emission origins. Additional measurement data are required to characterize the weekend–weekday and inter-seasonal patterns of PM.► PM2.5 and PM10 2.5 were investigated during polluted winter period in Hanoi. ► Variation in PM mass and composition were analyzed with meteorology and emission. ► Reconstructed mass and PMF model were used for source identification and apportionment. ► Contribution of local sources and long range transport to PM2.5 were analyzed.
Keywords: Fine particulate matter; EC/OC; Diurnal variation; Meteorology; Source apportionment; Hanoi;

Source categories and contribution of biomass smoke to organic aerosol over the southeastern Tibetan Plateau by Xuefang Sang; Zhisheng Zhang; Chuenyu Chan; Guenter Engling (113-123).
An intensive measurement campaign was conducted at a mountain and suburban site at the edge of the southeastern Tibetan Plateau during spring. Concentrations of PM2.5, carbonaceous species (OC and EC) and anhydrosugars (levoglucosan, mannosan and galactosan) as well as their ratios were utilized to identify possible biomass burning categories and contributions of biomass burning smoke to ambient aerosols. The average concentrations of levoglucosan and mannosan were 193.8 and 12.4 ng m−3, respectively at the mountain site, and 713 and 61.5 ng m−3 respectively at the suburban site. According to characteristic levoglucosan/mannosan (Lev/Man) and mannosan/galactosan (Man/Gal) ratios, we identified for the first time that mixed smoke particles (18.5, 72.3 and 9.1% for crop residues, softwood and hard wood respectively) derived from the study region and Southeast Asia contributed to the aerosol burden in the southeastern Tibetan Plateau. The biomass smoke contributions to organic carbon and organic matter were estimated to be 28.4% and 18.9–25.7% respectively at the mountain site and 38.3% and 33.5–45.4% respectively at the suburban site. The large contribution estimates indicate that biomass burning was an important anthropogenic/natural source of aerosol particles which impact regional atmospheric chemistry and climate in the southeastern Tibetan Plateau.► Spring time aerosol characterization in southeastern Tibetan Plateau. ► High levoglucosan and mannosan concentrations at a mountain and suburban site. ► Smoke aerosols from crop residues, softwood and hard wood burning in the study region and Southeast Asia. ► Biomass smoke contributions to OC and OM of up to 38.3 and 45.4%.
Keywords: Biomass burning; Levoglucosan; Anhydrosugars; Long-range transport; Tibetan Plateau;

Origin, transport, and vertical distribution of atmospheric pollutants over the northern South China Sea during the 7-SEAS/Dongsha Experiment by Sheng-Hsiang Wang; Si-Chee Tsay; Neng-Huei Lin; Shuenn-Chin Chang; Can Li; Ellsworth J. Welton; Brent N. Holben; N. Christina Hsu; William K.M. Lau; Simone Lolli; Chun-Chiang Kuo; Hao-Ping Chia; Chia-Yang Chiu; Chia-Ching Lin; Shaun W. Bell; Qiang Ji; Richard A. Hansell; Guey-Rong Sheu; Kai-Hsien Chi; Chi-Ming Peng (124-133).
During the spring of 2010, comprehensive in situ measurements were made for the first time on a small atoll (Dongsha Island) in the northern South China Sea (SCS), a key region of the 7-SEAS (the Seven South East Asian Studies) program. This paper focuses on characterizing the source origins, transport processes, and vertical distributions of the Asian continental outflows over the region, using measurements including mass concentration, optical properties, hygroscopicity, and vertical distribution of the aerosol particles, as well as the trace gas composition. Cluster analysis of backward trajectories classified 52% of the air masses arriving at ground level of Dongsha Island as having a continental origin, mainly from northern China to the northern SCS, passing the coastal area and being confined in the marine boundary layer (0–0.5 km). Compared to aerosols of oceanic origin, the fine mode continental aerosols have a higher concentration, extinction coefficient, and single-scattering albedo at 550 nm (i.e., 19 vs. 14 μg m−3 in PM2.5; 77 vs. 59 Mm−1 in β e ; and 0.94 vs. 0.90 in ω, respectively). These aerosols have a higher hygroscopicity (f at 85% RH = 2.1) than those in the upwind inland regions, suggesting that the aerosols transported to the northern SCS were modified by the marine environment. In addition to the near-surface aerosol transport, a significant upper-layer (3–4 km) transport of biomass-burning aerosols was observed. Our results suggest that emissions from both China and Southeast Asia could have a significant impact on the aerosol loading and other aerosol properties over the SCS. Furthermore, the complex vertical distribution of aerosols-coinciding-with-clouds has implications for remote-sensing observations and aerosol–cloud–radiation interactions.► First detailed aerosol optical properties in northern South China Sea were investigated. ► Back-trajectory analysis suggested 52% continental origin and 48% oceanic origin. ► Continental origin, mainly from Chinese coastal areas, with higher aerosol loading. ► Comparison with inland measurements, aerosol evolution and mixture were addressed. ► Upper-level (3–4 km) transport of biomass-burning aerosol was investigated by lidar.
Keywords: Aerosols; Optical properties; Back trajectory; UV lidar; Biomass burning;

Size resolved measurements of springtime aerosol particles over the northern South China Sea by Samuel A. Atwood; Jeffrey S. Reid; Sonia M. Kreidenweis; Steven S. Cliff; Yongjing Zhao; Neng-Huei Lin; Si-Chee Tsay; Yu-Chi Chu; Douglas L. Westphal (134-143).
Large sources of aerosol particles and their precursors are ubiquitous in East Asia. Such sources are known to impact the South China Sea (henceforth SCS), a sometimes heavily polluted region that has been suggested as particularly vulnerable to climate change. To help elucidate springtime aerosol transport into the SCS, an intensive study was performed on the remote Dongsha (aka Pratas) Islands Atoll in spring 2010. As part of this deployment, a Davis Rotating-drum Uniform size-cut Monitor (DRUM) cascade impactor was deployed to collect size-resolved aerosol samples at the surface that were analyzed by X-ray fluorescence for concentrations of selected elements. HYSPLIT backtrajectories indicated that the transport of aerosol observed at the surface at Dongsha was occurring primarily from regions generally to the north and east. This observation was consistent with the apparent persistence of pollution and dust aerosol, along with sea salt, in the ground-based dataset. In contrast to the sea-level observations, modeled aerosol transport suggested that the westerly flow aloft (∼700 hPa) transported smoke-laden air toward the site from regions from the south and west. Measured aerosol optical depth at the site was highest during time periods of modeled heavy smoke loadings aloft. These periods did not coincide with elevated aerosol concentrations at the surface, although the model suggested sporadic mixing of this free-tropospheric aerosol to the surface over the SCS. A biomass burning signature was not clearly identified in the surface aerosol composition data, consistent with this aerosol type remaining primarily aloft and not mixing strongly to the surface during the study. Significant vertical wind shear in the region also supports the idea that different source regions lead to varying aerosol impacts in different vertical layers, and suggests the potential for considerable vertical inhomogeneity in the SCS aerosol environment.► The marine boundary layer aerosol was a mixture of pollution, dust and sea salt. ► Strong vertical wind shear decoupled transport across the boundary layer inversion. ► Aerosol optical thickness was largely uncorrelated with surface mass concentrations.
Keywords: Asian aerosol; Aerosol vertical distributions; Marine aerosol; Dust aerosol; Biomass burning aerosol;

Influence of Asian continental outflow on the regional background ozone level in northern South China Sea by Chang-Feng Ou-Yang; Hsin-Cheng Hsieh; Sheng-Hsiang Wang; Neng-Huei Lin; Chung-Te Lee; Guey-Rong Sheu; Jia-Lin Wang (144-153).
Asian continental outflow is known to have very pronounced seasonality, which in turn can alter the trace gas contents of the Northern Hemisphere. In this study, field measurements were conducted during the spring of 2010, Dongsha, a small island situated between Taiwan and the Philippines, served as a remote site for monitoring surface ozone. Ozone was used as an effective indicator to distinguish between continental and marine air masses. Our measurements suggested that strong northeasterly winds arising from the winter Asian monsoon may have transported polluted air masses from the northern continent to locations as far south as Dongsha (latitude 20.70°N), as indicated by elevated ozone levels of approximately 60 ppbv. In contrast, during periodic calm periods when the monsoon subsided low ozone levels of about 30 ppb were detected, which is typical for marine air masses. This outflow of polluted air masses from the Asian continent and Taiwan facilitated by the winter monsoon was also successfully simulated using the Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model, version 5 (PSU/NCAR MM5) and the Taiwan Air Quality Model (TAQM).► It is the first continuous measurement of surface ozone in the northern SCS. ► The Asian continental outflows can affect latitudes as far south as Dongsha's. ► Dongsha is shown to be ideal for baseline establishment without land emissions.
Keywords: Ozone; Continental outflow; 7SEAS; South China Sea;

Dynamic variations of ultrafine, fine and coarse particles at the Lu-Lin background site in East Asia by Sheng-Chieh Chen; Shih-Chieh Hsu; Chuen-Jinn Tsai; Charles C.-K. Chou; Neng-Huei Lin; Chung-Te Lee; Gwo-Dong Roam; David Y.H. Pui (154-162).
The characteristics of atmospheric ultrafine particles (i.e. <100 nm, nanoparticles or PM0.1), PM2.5 and PM10 were studied at the Lulin Atmospheric Background Station (LABS, 2862 m a.s.l., Taiwan) as part of the 7SEAS/Dongsha campaign. Sampling was conducted in July and August of 2009 and September to November of 2010, during which two 96-h and four 72-h PM samples were taken. Real-time particle size distributions were measured continuously from July to August of 2009 and July to November of 2010. PM0.1, PM2.5 and PM10 were collected by using two MOUDIs (micro-orifice uniform deposit impactor, MSP 110) and a Dichotomous PM10 sampler (Andersen SA-241) while real-time size distributions of particles of 5.5–350 nm in diameter were measured by an SMPS (scanning mobility particle sizer, TSI 3936). Filter samples were analyzed for gravimetric mass and chemical compositions, including organic carbon (OC), element carbon (EC), water-soluble ions and trace elements. Meteorology parameters and gaseous O3 and CO concentrations were also monitored along with the SMPS data for studying particle nucleation, condensation, SOA (secondary organic aerosol) formation and long-range air pollutant transport at the LABS. SMPS data showed that nanoparticle concentrations at the LABS remained relatively stable at low level (∼300–500 #/cm3) during the nighttime (22:00–04:00), increased during daytime, and reached a maximum (∼2000–4000 #/cm3) in the afternoon (12:00–16:00). The NMD (number median diameter) showed an opposite trend with the peak number concentrations observed in the afternoon corresponding to the smallest NMD (20–40 nm). These results indicate the dominance of local sources rather than the transport from other atmospheric air because that the lifetime of nanoparticles was only few minutes. Chemical analysis of filter samples showed that the concentrations of trace elements K and Mn, which serve as biomass burning markers, were elevated in the fine particle fractions during November 9–12th when the air mass passed through South and Southeast Asia prior to reaching the LABS. The concentrations of K and Mn would have been low if the aerosols had local origins The biomass burning derived K was found in all fine particle samples at the LABS suggesting that the free troposphere around Taiwan is frequently impacted by the long-range transport of biomass burning plumes via the westerly winds.► Atmospheric PM0.1, PM2.5 and PM10 were studied at a background site. ► The concentration of biomass burning (BB) makers, K and Mn, elevated significantly. ► Free troposphere around Taiwan is impacted by BB plumes from Southeast Asia.
Keywords: Atmospheric aerosol; Ultrafine particle; Biomass burning; Biogenic aerosol; Chemical mass closure; Eastward transport;

Constraining aerosol optical models using ground-based, collocated particle size and mass measurements in variable air mass regimes during the 7-SEAS/Dongsha experiment by Shaun W. Bell; Richard A. Hansell; Judith C. Chow; Si-Chee Tsay; N. Christina Hsu; Neng-Huei Lin; Sheng-Hsiang Wang; Qiang Ji; Can Li; John G. Watson; Andrey Khlystov (163-173).
During the spring of 2010, NASA Goddard's COMMIT ground-based mobile laboratory was stationed on Dongsha Island off the southwest coast of Taiwan, in preparation for the upcoming 2012 7-SEAS field campaign. The measurement period offered a unique opportunity for conducting detailed investigations of the optical properties of aerosols associated with different air mass regimes including background maritime and those contaminated by anthropogenic air pollution and mineral dust. What appears to be the first time for this region, a shortwave optical closure experiment (λ = 550 nm) for both scattering and absorption was attempted over a 12-day period during which aerosols exhibited the most change. Constraints to the optical model included combined SMPS and APS number concentration data for a continuum of fine and coarse-mode particle sizes up to PM2.5. We also take advantage of an IMPROVE chemical sampler to help constrain aerosol composition and mass partitioning of key elemental species including sea-salt, particulate organic matter, soil, non sea-salt sulfate, nitrate, and elemental carbon. Achieving full optical closure is hampered by limitations in accounting for the role of water vapor in the system, uncertainties in the instruments and the need for further knowledge in the source apportionment of the model's major chemical components. Nonetheless, our results demonstrate that the observed aerosol scattering and absorption for these diverse air masses are reasonably captured by the model, where peak aerosol events and transitions between key aerosols types are evident. Signatures of heavy polluted aerosol composed mostly of ammonium and non sea-salt sulfate mixed with some dust with transitions to background sea-salt conditions are apparent in the absorption data, which is particularly reassuring owing to the large variability in the imaginary component of the refractive indices. Consistency between the measured and modeled optical parameters serves as an important link for advancing remote sensing and climate research studies in dynamic aerosol-rich environments like Dongsha.► First time attempt of optical closure at Dongsha in a dynamic aerosol environment. ► Observed optical properties are reasonably tracked by an optical model. ► Peak aerosol events and transitions between key types are captured. ► More resolved aerosol physicochemical datasets are needed for full optical closure.
Keywords: Aerosols; Scattering; Absorption;

Distribution of atmospheric mercury in northern Southeast Asia and South China Sea during Dongsha Experiment by Guey-Rong Sheu; Neng-Huei Lin; Chung-Te Lee; Jia-Lin Wang; Ming-Tung Chuang; Sheng-Hsiang Wang; Kai Hsine Chi; Chang-Feng Ou-Yang (174-183).
Northern South China Sea (SCS) is adjacent to major atmospheric mercury (Hg) emission source regions; however, studies concerning regional atmospheric Hg distribution and cycling are very limited. Accordingly, measurements of atmospheric Hg were conducted in March and April during the 2010 Dongsha Experiment to study its spatial and temporal distribution. Atmospheric Hg was measured at Hengchun and Dongsha Island (Taiwan), Da Nang (Vietnam), Chiang Mai (Thailand) and over the northern SCS. Atmospheric Hg concentrations ranged between 1.54 and 6.83 ng m−3, mostly higher than the Northern Hemisphere background value. Regional wind fields and backward trajectories indicated that the atmospheric Hg concentrations over northern SCS should principally reflect the export of the East Asian Hg emissions by northeast monsoon. However, significantly elevated Hg concentrations were always observed at Da Nang, possibly due to the influence of local Hg emissions. Chiang Mai is located in the intense biomass burning region in northern Thailand. Therefore, atmospheric Hg concentrations at Chiang Mai reflected the influence of regional biomass burning Hg emissions. Two dust storms were encountered at Dongsha Island, one on March 16 and the other on March 21, with atmospheric Hg enhancements. Compared with the 2008 summer values, elevated Hg levels were observed at Dongsha Island in the spring of 2010. Summer air masses were mainly from the deep SCS, representing relatively clean marine air. On the other hand, air masses were from the north in spring, passing eastern China or Taiwan prior to reaching Dongsha Island. Results of this research thus demonstrated the transport of atmospheric Hg from the East Asian continent to northern SCS by regional monsoon activity in spring, but special events, such as biomass burning and dust storms, can also cause enhancements of ambient Hg levels.► Atmospheric Hg was measured in Southeast Asia and over South China Sea (SCS). ► Elevated Hg concentrations were observed at all sites. ► Export of atmospheric Hg from the East Asian continent to SCS is demonstrated. ► Biomass burning and dust storm can also cause enhancements of Hg levels.
Keywords: Biomass burning; Dongsha Island; Dust storm; Indochina Peninsula;

Influence of the Southeast Asian biomass burnings on the atmospheric persistent organic pollutants observed at near sources and receptor site by Shun-Shiang Chang; Wen-Jhy Lee; Lin-Chi Wang; Neng-Huei Lin; Guo-Ping Chang-Chien (184-194).
Persistent organic pollutants (POPs) such as PCDD/Fs, PCBs, PBDD/Fs, PBBs and PBDEs are bio-accumulative, toxic, and susceptible to long-range transport (LRT). This study is the first that comprehensively discusses the long-range atmospheric transport behavior of these five groups of POPs. The main goal is to investigate the atmospheric characteristics of these POPs at the biomass burning sites of Chiang Mai in Thailand, and Da Nang in Vietnam, as well as the influence of the Southeast Asian biomass burnings on the Lulin Atmospheric Background Station (LABS) in Taiwan. Biomass burning in Southeast Asia is usually carried to remove the residues of agricultural activities. The ambient air in Da Nang seems to be more seriously affected by the local biomass burnings than that in Chiang Mai. The elevated atmospheric brominated POP (PBDD/Fs, PBBs and PBDEs) concentrations in Da Nang were attributed to the biomass burning and viewed as mostly unrelated to the local use of brominated flame retardants. In the spring of 2010, the mean atmospheric concentrations in LABS during the first and second Intensive Observation Periods (IOPs) were 0.00428 and 0.00232 pg I-TEQ Nm−3 for PCDD/Fs, 0.000311 and 0.000282 pg WHO-TEQ m−3 for PCBs, 0.000379 and 0.000449 pg TEQ Nm−3 for total PBDD/Fs, 0.0208 and 0.0163 pg Nm−3 for total PBBs, and 109 and 18.2 pg Nm−3 for total PBDEs, respectively. These values represent the above concentrations due to the Southeast Asian biomass burnings. The affected atmospheric POP concentrations at the LABS were still at least one order lower than those in other atmospheric environments, except for the PBDE concentrations during the first IOP (109 pg Nm−3), which was surprisingly higher than those in Taiwanese metal complex areas (93.9 pg Nm−3) and urban areas (34.7 pg Nm−3). Atmospheric POP concentrations do not seem to dramatically decrease during long-range transport, and the reasons for this need to be further investigated.► Biomass burnings elevate the atmospheric brominated POP concentrations in Da Nang. ► Backward trajectory model shows air masses transport from SE Asia to LABS in Taiwan. ► The atmospheric POPs of LABS were affected by the SE Asia biomass burning.
Keywords: Biomass burning; Long-range transport; PCDD/Fs; PBDEs; POPs;

Atmospheric PCDD/F measurement in Taiwan and Southeast Asia during Dongsha Experiment by Ngo Thi Thuan; Kai Hsien Chi; Sheng-Hsiang Wang; Moo Been Chang; Neng-Huei Lin; Guey-Rong Sheu; Chi-Ming Peng (195-202).
The international campaign of Dongsha Experiment was conducted in the northern Southeast Asian region during March–May 2010. To address the effects of long-range transport on the persistent organic pollutants and further understand the PCDD/F contamination in Vietnam, atmospheric PCDD/Fs were evaluated at a coastal station (Pingtung County, Sites A) in southern Taiwan, remote island station in South China Sea (Dongsha Island, Site B) and coastal station (Da Nang City, Site C) in central Vietnam during different sampling periods in this study. The measurements indicated that the atmospheric PCDD/F concentrations were 1.01–27.4 fg I-TEQ/m3 (n = 22), 1.52–10.8 fg I-TEQ/m3 (n = 17) and 23.4–146 fg I-TEQ/m3 (n = 16) at Sites A, B and C, respectively, during different periods in 2010. In March 2010, an Asian dust storm (ADS) that originated in Gobi deserts eventually reached populated areas of East Asia, including Taiwan and the island in northern South China Sea. During the ADS episode, measurements made in southern Taiwan and South China Sea on 16 and 21 March 2010 indicate that the atmospheric PCDD/F concentration increased 6.5 and 6.9 times at Sites A and B, respectively. Furthermore, the significantly higher PCDD/F concentrations and contents in suspended particles (134–546 pg I-TEQ/g-TSP) were measured at Site C in the central Vietnam. In addition, the distribution of PCDD/F congeners measured in Central Vietnam was quite different from those measured at other stations with high PCDD distribution (>80%) especially in OCDD (>70%). During the Vietnam conflict, United States (US) forces had sprayed a greater volume of defoliant with higher PCDD/F contents than originally estimated. We consider that the high fraction of PCDDs observed in Vietnam probably originated as anthropogenic emission from specific source in Vietnam.► During Asian dust storm episode, atmospheric PCDD/Fs significantly increased in South China Sea. ► Dongsha Experiment presents the first measurements of higher atmospheric PCDD/Fs in Vietnam. ► Higher fractions of ambient PCDDs in Da Nang city probably originated as Agent Orange contamination.
Keywords: Dioxin; Vietnam; Aerosol; Atmosphere; Agent Orange;

Evaluation of the distributions of ambient PCDD/Fs at remote locations in and around Taiwan by Kai Hsien Chi; Chuan-Yao Lin; Sheng-Hsiang Wang; Neng-Huei Lin; Guey-Rong Sheu; Chung-Te Lee (203-210).
Recently, the high PCDD/F emissions observed in the coastal provinces of eastern China have raised global concerns over their adverse effects on human health. To address the effects of the long-range transport of persistent organic pollutants, the observations of atmospheric PCDD/F pollution were conducted across Southeast Asian in this study. Atmospheric PCDD/F levels were evaluated at two background stations (Sites A and B) in Taiwan, three remote islands (Sites C, D and E) around Taiwan and at Dongsha Island (Site F) in South China Sea at various times. Significantly lower atmospheric PCDD/F concentrations (1.24–7.75 fg I-TEQ m 3) and PCDD/F contents (3.45–49.1 pg I-TEQ/g-TSP) in total suspended particles (TSPs) were measured during the summer season. Based on a 72-h backward trajectory analysis conducted for the sampling sites used in this study, the air mass containing theses low levels had originated from the Pacific Ocean and South China Sea during the summer. The highest PCDD/F concentrations (10.2–65.2 fg I-TEQ m 3) and PCDD/F contents (132–620 pg I-TEQ/g-TSP) in ambient air were measured in northern Taiwan (Site A) and at two islands (Site C and Site E) close to mainland China during the northeast monsoon periods. In the meantime, the PCDF compounds in ambient air also increased from 52–54% to 65–75% at those sampling sites. Based on these measurements and corresponding trajectory analysis, we conclude that the significant increase in atmospheric PCDD/Fs measured during the northeast monsoon period in this study was attributable to the long-range transport of emissions from the coastal regions of mainland China.► In South China Sea, there are not any combustion sources within 300 km of Dongsha Island. ► Lower PCDD/Fs (0.58 fg I-TEQ m3) were measured at Dongsha Island during southwest monsoon period. ► During northeast monsoon period, high fraction of PCDF compounds was observed in northern Taiwan. ► The higher PCDD/Fs (78.7 fg I-TEQ m3) were measured in Matsu Island close to mainland China. ► The increasing PCDD/Fs observed in this study were attributed to long-range transport from China.
Keywords: Dioxin; Dongsha Island; Aerosol; Long-range transport;

Daily ambient PM2.5 was collected during 8 September to 5 October (Julian Days, JDs 252–279), 2008 in Singapore to investigate impacts of transboundary biomass burning smoke on distribution among C2–C5 dicarboxylic acids (DCAs) and corresponding dicarboxylate salts (DCS) in the tropical urban atmosphere. Quantification of DCAs and DCS were performed using solvent and water extraction followed by chromatography analyses via GC–MS and ion chromatography. The averaged PM2.5 and PM10 concentrations from September 19–30 (JDs 263–274) were concurrently elevated by ∼40% due to the transboundary smoke. During this same period, C2–C5 total dicarboxylates (TDCAS, summation of DCAs and DCS), on average, increased more than two times, with C2-TDCAS accounted for in average 80% of the C2–C5 TDCAS. This demonstrates that the transboundary smoke enriched C2–C5 TDCAS more than PM2.5 in the urban environment. In the presence of the transboundary smoke, the averaged concentration ratios of C2–C5 DCS to corresponding DCA were 13.4, 2.9, 1.0, and 1.4 with oxalate salts exhibiting the highest concentration (355.0 ng m−3). The transboundary smoke increased malic acid concentration more than 3.5 times, which is the largest relative increase among the quantified TDCAS. Considering that malic acid is mainly generated through ambient photooxidation, such significant increase in malic acid demonstrates more prominent photooxidation incurred by the smoke.► DCAs and DCS reflect impacts of transboundary smoke more than PM2.5. ► Oxalate is most abundant among quantified species, >10 times of C2 DCS. ► Among speciated DCAs, transboundary smoke elevates malic acid the most. ► Significant increase in malic acid indicates stronger photooxidation. ► Transboundary biomass burning smoke triggers more prominent photooxidation.
Keywords: PM2.5; Photooxidation; Levoglucosan; Transboundary; Southeast Asia;

Analysis of source regions for smoke events in Singapore for the 2009 El Nino burning season by Samuel A. Atwood; Jeffrey S. Reid; Sonia M. Kreidenweis; Liya E. Yu; Santo V. Salinas; Boon Ning Chew; Rajasekhar Balasubramanian (219-230).
As part of the 7 SouthEast Asian Studies (7SEAS) program, a solar radiation and chemistry sampling site (“supersite”) was developed at the National University of Singapore (NUS) to monitor regional air quality. The first intensive operations period for this site occurred between August and October 2009, a period that coincided with a moderate El Nino event and enhanced tropical burning, particularly in peatlands. We use data from this period to analyze the transport of biomass burning emissions in the Maritime Continent (MC) to the NUS supersite. An overview of the aerosol environment is provided for Singapore, followed by more detailed discussion of four aerosol events. The 2009 burning season was similar to those described in previous analyses, which showed that fire activity begins in the western half of the MC in Sumatra and propagates eastward in time. Similarly, agricultural burning occurs first, generally followed by deforestation and peatland fires. Some of the biomass burning emissions make their way into the free troposphere, where they are transported regionally by the prevailing wind patterns. Our analyses show that the seasonal winds at 850 hPa (∼1500 m) shift transport patterns from source regions to the southwest of Singapore, to regions to the southeast over the course of the summer monsoon, patterns that allow Singapore to be impacted by peak burning regions in the MC. In contrast, winds at the surface are more typically from the south and southeast, demonstrating the prevalence of vertical wind shear over the region. As a result of the variable source regions influencing different levels of the atmosphere over Singapore, in-situ surface observations of aerosol mass concentrations are not always consistent with inferences of the presence of enhanced aerosol concentration from column optical depth. Our findings confirm the complexity of aerosol sources and transport over the MC, and the key role that biomass burning emissions play in influencing column aerosol optical depth and total particulate mass concentrations at the surface. The sea-level altitude of the NUS supersite means that non-local pollution transported above the boundary layer cannot be reliably sampled and characterized, but the combined effects of local emissions and downward-mixed, non-local pollutants in Singapore were consistently measured.
Keywords: Maritime Continent; Biomass burning; Aerosol transport; Receptor modeling; Summer monsoon; Air quality;

First measurements of aerosol optical depth and Angstrom exponent number from AERONET's Kuching site by Santo V. Salinas; Boon N. Chew; M. Mohamad; M. Mahmud; Soo C. Liew (231-241).
We report our first measurements, over the 2011 dry season period, of aerosol optical depth, Angstrom exponent number and its fine mode counterpart obtained from photometric measurements at AERONET's newest site located at the city of Kuching, Sarawak, East Malaysia. This site was set up as part of the collaborative efforts of the Seven South East Asian Studies (7SEAS) regional aerosol measurements initiative. Located at the converging zone between peninsular Malaysia and the land masses of Sumatra, Borneo, Java and Sulawesi, this site is expected to provide first hand evidence about the physical and optical characteristics of the regional aerosol environment, specially during the biomass burning months. Moreover, given its relative proximity to our Singapore radiation measurement super-site, Kuching is expected to provide further insight on aerosol transport pathways caused by seasonal winds transporting smoke to other parts of the maritime continent and the South Asia region.► In general, Kuching aerosol environment is relatively clean with low aerosol loading. ► Increased aerosol loading correlates with regional episodes of biomass burning. ► AOD and Angstrom number indicated a prevailing fine mode aerosol environment. ► Aerosols belongs mostly to urban, fossil fuel (aircraft activity) and biomass burning. ► Dry months, August–September, showed high aerosol loading. November the least.
Keywords: Aerosols; Biomass burning; AERONET; Kuching; South East Asia;

Biomass burning from the combustion of agricultural wastes and forest materials is one of the major sources of air pollution. The objective of the study is to investigate the major contribution of the biomass open burning events in the island of Borneo, Indonesia to the degradation of air quality in equatorial Southeast Asia. A total of 10173 active fire counts were detected by the MODIS Aqua satellite during August 2004, and consequently, elevated the PM10 concentration levels at six air quality stations in the state of Sarawak, in east Malaysia, which is located in northwestern Borneo. The PM10 concentrations measured on a daily basis were above the 50 μg m−3 criteria as stipulated by the World Health Organization Air Quality Guidelines for most of the month, and exceeded the 24-h Recommended Malaysian Air Quality Guidelines of 150 μg m−3 on three separate periods from the 13th to the 30th August 2004. The average correlation between the ground level PM10 concentrations and the satellite derived aerosol optical depth (AOD) of 0.3 at several ground level air quality stations, implied the moderate relationship between the aerosols over the depth of the entire column of atmosphere and the ground level suspended particulate matter. Multiple regression for meteorological parameters such as rainfall, windspeed, visibility, mean temperature, relative humidity at two stations in Sarawak and active fire counts that were located near the centre of fire activities were only able to explain for 61% of the total variation in the AOD.The trajectory analysis of the low level mesoscale meteorological conditions simulated by the TAPM model illustrated the influence of the sea and land breezes within the lowest part of the planetary boundary layer, embedded within the prevailing monsoonal southwesterlies, in circulating the aged and new air particles within Sarawak.► Moderate correlation exists between the ground level PM10 concentrations and AOD from biomass burning activities. ► Dispersion of smoke limited when the equatorial wind regime is weak. ► Weak monsoon, land–sea breeze conditions and topography increased smoke is in northern Borneo.
Keywords: Biomass open burning; Southeast Asia; Transboundary haze; Aerosols;

This paper presents an emission inventory (EI) for biomass open burning (OB) sources including forest, agro-residue and municipal solid waste (MSW) in Indonesia for year 2007. The EI covered toxic air pollutants and greenhouse gases (GHGs) and was presented as annual and monthly average for every district, and further on a grid of 0.25° × 0.25°. A rigorous analysis of activity data and emission factor ranges was done to produce the low, best and high emission estimates for each species. Development of EI methodology for MSW OB which, to our best knowledge, has not been presented in detail in the literature was a focus of this paper. The best estimates of biomass OB emission of toxic air pollutants for the country, in Gg, were: 9.6 SO2; 98 NO x ; 7411 CO; 335 NMVOC; 162 NH3; 439 PM10; 357 PM2.5; 24 BC; and 147 OC. The best emission estimates of GHGs, in Gg, were: 401 CH4, 57,247 CO2; and 3.6 N2O. The low and high values of the emission estimates for different species were found to range from −86% to +260% of the corresponding best estimates. Crop residue OB contributed more than 80% of the total biomass OB emissions, followed by forest fire of 2–12% (not including peat soil fire emission) and MSW (1–8%). An inter-annual active fires count for Indonesia showed relatively low values in 2007 which may be attributed to the high rainfall intensity under the influence of La Niña climate pattern in the year. Total estimated net climate forcing from OB in Indonesia was 110 (20 year horizon) and 73 (100 year horizon) Tg CO2 equivalents which is around 0.9–1.1% of that reported for the global biomass OB for both time horizons. The spatial distribution showed higher emissions in large urban areas in Java and Sumatra Island, while the monthly emissions indicated higher values during the dry months of August–October.► Emission inventory for biomass open burning in Indonesia was conducted for 2007. ► Best estimates and ranges of pollutants and GHG emission were produced. ► Methodology for solid waste open burning emission inventory was developed. ► Monthly and gridded (0.25°) emissions were obtained for 3D modeling. ► Climate forcing associated with Indonesian biomass open burning was assessed.
Keywords: Emission inventory; Biomass open burning; Solid waste; Uncertainty analysis; Climate forcing;

Estimated range of black carbon dry deposition and the related snow albedo reduction over Himalayan glaciers during dry pre-monsoon periods by Teppei J. Yasunari; Qian Tan; K.-M. Lau; Paolo Bonasoni; Angela Marinoni; Paolo Laj; Martin Ménégoz; Toshihiko Takemura; Mian Chin (259-267).
One of the major factors attributed to the accelerated melting of Himalayan glaciers is the snow darkening effect of atmospheric black carbon (BC). The BC is the result of incomplete fossil fuel combustion from sources such as open biomass burning and wood burning cooking stoves. One of the key challenges in determining the darkening effect is the estimation uncertainty of BC deposition (BCD) rate on surface snow cover. Here we analyze the variation of BC dry deposition in seven different estimates based on different dry deposition methods which include different atmospheric forcings (observations and global model outputs) and different spatial resolutions. The seven simulations are used to estimate the uncertainty range of BC dry deposition over the southern Himalayas during pre-monsoon period (March–May) in 2006. Our results show BC dry deposition rates in a wide range of 270–4700 μg m−2 during the period. Two global models generate higher BC dry deposition rates due to modeled stronger surface wind and simplification of complicated sub-grid surface conditions in this region. Using ice surface roughness and observation-based meteorological data, we estimate a better range of BC dry deposition rate of 900–1300 μg m−2. Under dry and highly polluted conditions, aged snow and sulfate-coated BC are expected to possibly reduce visible albedo by 4.2–5.1%. Our results suggest that for estimating aerosol-induced snow darkening effects of Himalaya snowpacks using global and regional models, realistic physical representation of ice or snow surface roughness and surface wind speed are critical in reducing uncertainties on the estimate of BC deposition over snow surface.► Black carbon emission is significant over Indo-Gangetic Plain. ► We estimated possible wider range of black carbon dry deposition over the southern Himalayas. ► Its impact on snow albedo reductions over Himalayan glaciers was also estimated. ► Surface wind and roughness affect the deposition amount and snow albedo reduction. ► Surface parameterization in transport model is important for their accurate estimate.
Keywords: Biomass burning; Himalayas; Black carbon; Deposition; Snow melting;

Chemical characterization of aerosols in the equatorial atmosphere over the Indian Ocean by Rajasekhar Balasubramanian; Sathrugnan Karthikeyan; John Potter; Oliver Wurl; Caroline Durville (268-276).
The region of the Indian Ocean and adjacent countries has received increased attention in recent years in the context of particulate air pollution. Aerosol samples were collected over the equatorial Indian Ocean during a one-year-long sailing cruise that covered the northeast and southwest monsoons, and an inter-monsoon period. The concentrations of airborne particulate matter (PM), selected metals and water-soluble ions were measured. In general, the PM concentrations were influenced by the proximity of sampling locations to land and air mass origins. The enrichment of metals in PM relative to those in the crustal material was very high (up to 40,000). The metal concentrations were significantly higher in PM samples which were influenced by volcanic emissions from the land masses of Indonesia. Volcanic plumes were traced using backward air mass trajectory and chemical tracers, and identified as a major particulate pollution source to the otherwise pristine air of the southern hemisphere of the Indian Ocean. NO 3 − , NH 4 + and SO 4 2 − were low in aerosols collected over the open ocean, but a linear relationship between NH 4 + and SO 4 2 − indicates their importance in the formation of cloud condensation nuclei.► Particulate samples were collected during the course of a year-long sailing cruise across the Indian Ocean. ► The concentrations of selected metals and water-soluble ions were measured. ► Metal concentrations were influenced by volcanic emissions from the land masses of Indonesia. ► Overall, the air masses collected south of the equator were found to be polluted.
Keywords: Aerosols; Trace metals; Indian ocean; Volcanic emissions;

This study is conducted to identify the synoptic weather patterns that are prone to cause high carbon monoxide (CO) concentrations observed at a mountain site, Lulin atmospheric background station (LABS), in Taiwan due to the biomass-burning activity in Southeast (SE) Asia. LABS is recognized as a clean background station. The study period targets the biomass-burning season (February to May) from 2007 to 2010. The synoptic weather patterns were classified using a two-stage clustering method with inputs from the Weather Research and Forecasting (WRF) meteorological model simulation result in a 27-km spatial grid. A 9-km resolution WRF modeling was performed additionally for 13 to 26 March 2007, when a high CO concentration reaching 500 ppb was observed at LABS. The simulation result indicates that not only the existence of the thermal forcing induced low pressure system formed in Indochina, but also the presence of the high terrain located in the northern part of SE Asia that further forced the uplift of the biomass-burning emissions. On the other hand, when the northeasterly monsoonal flow is strong enough and intruding into Indochina, this would hinder the development of the thermal low and weaken the upward movements, in turn preventing the transport of biomass-burning emissions from Indochina to the area of Taiwan. The simulation results also demonstrate that the location of the SE Asia high pressure system has a moderate effect on the particle dispersion path in the upper level.
Keywords: Weather classification; Synoptic weather pattern; Biomass-burning; Carbon monoxide; Transport mechanism;

Impact assessment of biomass burning on air quality in Southeast and East Asia during BASE-ASIA by Kan Huang; Joshua S. Fu; N. Christina Hsu; Yang Gao; Xinyi Dong; Si-Chee Tsay; Yun Fat Lam (291-302).
A synergy of numerical simulation, ground-based measurement and satellite observation was applied to evaluate the impact of biomass burning originating from Southeast Asia (SE Asia) within the framework of NASA's 2006 Biomass burning Aerosols in Southeast Asia: Smoke Impact Assessment (BASE-ASIA). Biomass burning emissions in the spring of 2006 peaked in March–April when most intense biomass burning occurred in Myanmar, northern Thailand, Laos, and parts of Vietnam and Cambodia. Model performances were reasonably validated by comparing to both satellite and ground-based observations despite overestimation or underestimation occurring in specific regions due to high uncertainties of biomass burning emission. Chemical tracers of particulate K+, OC concentrations, and OC/EC ratios showed distinct regional characteristics, suggesting biomass burning and local emission dominated the aerosol chemistry. CMAQ modeled aerosol chemical components were underestimated at most circumstances and the converted AOD values from CMAQ were biased low at about a factor of 2, probably due to the underestimation of biomass emissions. Scenario simulation indicated that the impact of biomass burning to the downwind regions spread over a large area via the Asian spring monsoon, which included Southern China, South China Sea, and Taiwan Strait. Comparison of AERONET aerosol optical properties with simulation at multi-sites clearly demonstrated the biomass burning impact via long-range transport. In the source region, the contribution from biomass burning to AOD was estimated to be over 56%. While in the downwind regions, the contribution was still significant within the range of 26%–62%.► We model biomass burning in Southeast Asia which has been rarely studied. ► Impact of biomass burning in both source and downwind regions are assessed. ► Contributions from biomass burning to aerosol are quantatively determined. ► Model evaluations suggest biomass burning emission inventory should be improved.
Keywords: Biomass burning; Southeast Asia; CMAQ; Long-range transport; Aerosol chemical property; Aerosol optical property;