[1] Simultaneous measurements of atmospheric organic and elemental carbon (OC and EC) were taken during winter and summer seasons at 2003 in 14 cities in China. Daily PM 2.5 samples were analyzed for OC and EC by the Interagency Monitoring of Protected Visual Environments (IMPROVE) thermal/optical reflectance protocol. Average PM 2.5 OC concentrations in the 14 cities were 38.1 mg m À3 and 13.8 mg m À3 for winter and summer periods, and the corresponding EC were 9.9 mg m À3 and 3.6 mg m À3 , respectively. OC and EC concentrations had summer minima and winter maxima in all the cities. Carbonaceous matter (CM), the sum of organic matter (OM = 1.6 Â OC) and EC, contributed 44.2% to PM 2.5 in winter and 38.8% in summer. OC was correlated with EC (R 2 : 0.56-0.99) in winter, but correlation coefficients were lower in summer (R 2 : 0.003-0.90). Using OC/EC enrichment factors, the primary OC, secondary OC and EC accounted for 47.5%, 31.7% and 20.8%, respectively, of total carbon in Chinese urban environments. More than two thirds of China's urban carbon is derived from directly emitted particles. Average OC/EC ratios ranged from 2.0 to 4.7 among 14 cities during winter and from 2.1 to 5.9 during summer. OC/EC ratios in this study were consistent with a possible cooling effect of carbonaceous aerosols over China.

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at Lulang, a high-altitude (>3300m above sea level) site on the southeast Tibetan Plateau (TP); objectives were to determine chemical characteristics of the aerosol and identify its major sources. We report aerosol (total suspended particulate, TSP) mass levels and the concentrations of selected elements, carbonaceous species, and water-soluble inorganic ions. Significant buildup of aerosol mass and chemical species (organic carbon, element carbon, nitrate, and sulfate) occurred during the premonsoon, while lower concentrations were observed during the monsoon. Seasonal variations in aerosol and chemical species were driven by precipitation scavenging and atmospheric circulation. Two kinds of high-aerosol episodes were observed: one was enriched with dust indicators (Fe and Ca , and Fe. The TSP loadings during the latter were 3 to 6 times those on normal days. The greatest aerosol optical depths (National Centers for Environmental Protection/National Center for Atmospheric Research reanalysis) occurred upwind, in eastern India and Bangladesh, and trajectory analysis indicates that air pollutants were transported from the southwest. Northwesterly winds brought high levels of natural emissions (Fe, Ca 2+ ) and low levels of pollutants (SO 4 2À , NO 3 À , K + , and EC); this was consistent with high aerosol optical depths over the western deserts and Gobi. Our work provides evidence that both geological and pollution aerosols from surrounding regions impact the aerosol population of the TP.

[1] During spring 2002, three dust storm events were monitored by filter sampling in Xi'an near an Asian dust source region of northwest China. The carbonate (CO 3 2À ) fraction was determined by sample acidification and thermal evolution. The CO 3 2À accounted for 8.0 ± 0.8% of particles with aerodynamic diameter 2.5 mm (PM 2.5 ) during dust storms and 4.7 ± 3.0% of PM 2.5 between storms. The ratios of calcium to carbonate carbon were consistent with those of calcite (CaCO 3 ). The d C and d18 O abundances in dust storm samples were À2.7 ± 0.7% and À5.8 ± 1.5%, which differed from À8.3 ± 1.9% for d 13 C and À10.8 ± 2.0% for d 18O during normal conditions. The d 13C is positively correlated with d 18O values (r = 0.78). This first measurement of isotopic abundance in Asian dust indicates the potential to quantify its contribution at distant locations using receptor models. By increasing the alkalinity of ocean water in the Pacific Ocean and buffering the atmospheric acidity of east Asia, the large amounts of airborne CO 3 2À (as high as 44.8 Tg yr À1) entrained by Asian dust may provide an important atmospheric alkaline carbon reservoir for large-scale climatic and environmental changes.

We present a 3-year time series of lead (Pb) and mercury (Hg) concentrations and isotope signatures in total suspended particulate (TSP) matter and as total gaseous Hg (TGM) in Xi'an, Northwestern China. Mean concentrations of TSP (299 ± 120 μg m), Pb (0.33 ± 0.15 μg m) and Hg (0.64 ± 0.54 ng m), and TGM (5.7 ± 2.7 ng m) were elevated. We find that atmospheric Pb levels in winter in Xi'an have decreased by 4.6% per year since 2003, yet remain elevated relative to air quality guidelines and therefore a major health concern. δHg and ΔHg averaged -0.80 ± 0.30‰ (1σ) and -0.02 ± 0.10‰ (1σ) and δHg and ΔHg averaged -0.08 ± 0.41‰ (1σ) and 0.00 ± 0.04‰ (1σ). Relative to raw coal from Shaanxi and surrounding provinces, δHg is enriched in the light Hg isotopes, whereas δHg is enriched in the heavy isotopes. TSP and TGM ΔHg signatures are indistinguishable from raw coal, indicating little photochemical mass independent fractionation of atmospheric Hg in the near-field urban-industrial environment. δHg correlates significantly with TGM levels (r = 0.3, p < 0.01) and likely reflects binary mixing of local industrial TGM emissions with global background TGM.

[1] Continental China has been recognized as one of the most important sources of atmospheric mineral dust particles (called Kosa in Japan, which literally means yellow sand). Many investigators have pointed out the importance of study of the long-range transport of mineral dust particles and their modifications in this process even during the nondust storm periods. Because of these modifications, particles can change their radiative properties and their ability to be a condensation nucleus. Therefore it is important to examine the composition of individual mineral particles in their source region and compare these particles with those after long-range transport. A number of investigations have been carried out on the subject; however, the amount of data is still insufficient. Samples of aerosol particles were collected in Dunhuang, China, in different seasons in 2001 and 2002 during the ACE-Asia campaign. The collected particles were examined using a scanning electron microscope equipped with an energy dispersive X-ray analyzer. The particles in all the samples were mainly mineral particles. Similar types of mineral particles were found in the free troposphere over Japan. A number of differences were found between the particles collected in China and those collected over Japan, and these differences can be explained by chemical modifications that occurred in the particles during their transport from China to Japan. Approximately 40-45% of mineral particles mixed internally with sulphate during their transport in the troposphere. Also, the particles collected over Japan were found to be different from those obtained in ground-based measurements in Nagasaki, Nagoya, and Fukuoka, Japan (reported by other research groups). The portion of mineral particles that mixed internally with sea salt and sulphates was considerably smaller than for the samples obtained in Japan near the ground. It is important to take this fact into account while investigating the impact of mineral particles on the biogeochemical cycle and climate.