Chemical characterization of PM2.5 from a southern coastal city of China:applications of modeling and chemical tracers in demonstrationof regional transport

An intensive sampling campaign of airborne fine particles (PM2.5) was conducted at Sanya, a coastal city in Southern China, from January to February 2012. Chemical analyses and mass reconstruction were used identify potential pollution sources and investigate atmospheric reaction mechanisms. A thermodynamic model indicated that low ammonia and high relative humidity caused the aerosols be acidic and that drove heterogeneous reactions which led to the formation of secondary inorganic aerosol. Relationships among neutralization ratios, free acidity, and air-mass trajectories suggest that the atmosphere at Sanya was impacted by both local and regional emissions. Three major transport pathways were identified, and flow from the northeast (from South China) typically brought the most polluted air to Sanya. A case study confirmed strong impact from South China (e.g., Pearl River Delta region) (contributed 76.8% to EC, and then this result can be extended to primary pollutants) when the northeast winds were dominant. The Weather Research Forecasting Black carbon model and trace organic markers were used to apportion local pollution versus regional contributions. Results of the study offer new insights into the atmospheric conditions and air pollution at this coastal city

Effect of biomass burning on black carbon (BC) in South Asia and Tibetan Plateau: The analysis of WRF-Chem modeling

The focus of this study is to evaluate the impact of biomass burning (BB) from South Asia and Southeast Asia on the glaciers over the Tibetan Plateau. The seasonality and long-term trend of biomass fires measured by Terra and Aqua satellite data from 2010 to 2016 are used in this study. The analysis shows that the biomass burnings were widely dispersed in the continental of Indian and Southeast Asia and existed a strong seasonal variation. The biomass burnings in winter (January) were relatively weak and scattered and were significantly enhanced in spring (April). The highest biomass burnings located in two regions. One was along the foothill of Himalayas, where is a dense population area, and the second located in Southeast Asia. Because these two high biomass burning regions are close to the Tibetan Plateau, they could have important effects on the BC deposition over the glaciers of the Tibetan Plateau. In order to study the effect of BB emissions on the deposition over the glaciers in the Tibetan Plateau, a regional chemical model (WRF-Chem; Weather Research and Forecasting Chemical model) was applied to simulate the BC distributions and the transport from BB emission regions to the glaciers in Tibetan Plateau. The result shows that in winter (January), due to the relatively weak BB emissions, the effect of BB emissions on BC concentrations was not significant. The BC concentrations resulted from BB emissions ranged from 0.1 to 2.0 &mu;g/m3, with high concentrations distributed along the foothill of Himalayas and the southeastern Asia region. Due to the relative low BC concentrations, there was insignificant effect of BB emissions on the deposition over the glaciers in the Tibetan Plateau in winter. However, the BB emissions were highest in spring (April), producing high BC concentrations. For example, along the Himalayas Mountain and in the southeastern Asia region, The BC concentrations ranged from 2.0 to 6.0 &mu;g/m3. In addition to the high BC concentrations, there were also west and south prevailing winds in these regions. As a result, the BC particles were transported to the glaciers in the Tibetan Plateau, causing significant deposition of BC particles on the snow surface of the glaciers. This study suggests that the biomass burning emissions have important effects on the BC deposition over the glaciers in the Tibetan Plateau, and the contaminations of glaciers could have significant impact on the melting of snow in the Tibetan Plateau, causing some severe environmental problems, such as the water resources.</p

Black carbon (BC) in a northern Tibetan mountain: effect of Kuwait fires on glaciers

The black carbon (BC) deposition on the ice core at Muztagh Ata Mountain, northern Tibetan Plateau, was analyzed. Two sets of measurements were used in this study, which included the air samplings of BC particles during 2004&ndash;2006 and the ice core drillings of BC deposition during 1986&ndash;1994. Two numerical models were used to analyze the measured data. A global chemical transportation model (MOZART-4) was used to analyze the BC transport from the source regions, and a radiative transfer model (SNICAR) was used to study the effect of BC on snow albedo. The results show that during 1991&ndash;1992, there was a strong spike in the BC deposition at Muztagh Ata, suggesting that there was an unusual emission in the upward region during this period. This high peak of BC deposition was investigated by using the global chemical transportation model (MOZART-4). The analysis indicated that the emissions from large Kuwait fires at the end of the first Gulf War in 1991 caused this high peak of the BC concentrations and deposition (about 3&ndash;4 times higher than other years) at Muztagh Ata Mountain, suggesting that the upward BC emissions had important impacts on this remote site located on the northern Tibetan Plateau. Thus, there is a need to quantitatively estimate the effect of surrounding emissions on the BC concentrations on the northern Tibetan Plateau. In this study, a sensitivity study with four individual BC emission regions (Central Asia, Europe, the Persian Gulf, and South Asia) was conducted by using the MOZART-4 model. The result suggests that during the &ldquo;normal period&rdquo; (non-Kuwait fires), the largest effect was due to the Central Asia source (44 %) during the Indian monsoon period, while during the non-monsoon period, the largest effect was due to the South Asia source (34 %). The increase in radiative forcing increase (RFI) due to the deposition of BC on snow was estimated by using the radiative transfer model (SNICAR). The results show that under the fresh snow assumption, the estimated increase in RFI ranged from 0.2 to 2.5 W m&minus;2, while under the aged snow assumption, the estimated increase in RFI ranged from 0.9 to 5.7 W m&minus;2. During the Kuwait fires period, the RFI values increased about 2&ndash;5 times higher than in the &ldquo;normal period&rdquo;, suggesting a significant increase for the snow melting on the northern Tibetan Plateau due to this fire event. This result suggests that the variability of BC deposition at Muztagh Ata Mountain provides useful information to study the effect of the upward BC emissions on environmental and climate issues in the northern Tibetan Plateau. The radiative effect of BC deposition on the snow melting provides important information regarding the water resources in the region.</p

PM2.5 from the Guanzhong Plain: Chemical composition andimplications for emission reductions

Atmospheric particulate matter (PM) affects important environmental issues including air quality, regional and global climates, and human health. A one-year sampling campaign for PM2.5 was conducted at six locations in Guanzhong Plain, including the cities of Xi&#39;an, Weinan and Baoji, from March 2012 to March 2013. The 24-h average PM2.5 mass concentration was 134.7&nbsp;&mu;g&nbsp;m&minus;3, that substantially exceeds the National Ambient Air Quality Standard level of 35&nbsp;&nbsp;&mu;g&nbsp;m&minus;3. The highest loadings of both organic and elemental carbon (OC and EC) occurred in winter: EC co-varied with OC but showed less variability, presumably due to more stable emissions. The greatest contributions of secondary inorganic ions (SO42&minus;, NO3&minus; and NH4+) to the total quantified ions also were seen in winter, presumably due to gaseous precursors from coal combustion and biomass burning. Two high PM episodes occurred, one in the autumn and the other in winter. During the autumn episode, regional pollution from biomass burning raised the concentrations of secondary ions while coal combustion was a strong influence during the winter episode. Modeling simulations suggest that the control measures on both primary emissions and secondary aerosol precursors including SO2, NOx, and NH3 are needed to reduce the PM levels of the region.</p

Physicochemical characteristics of black carbonaerosol and its radiative impact in a pollutedurban area of China

Black carbon (BC) aerosol plays an important role in the Earth&rsquo;s radiative balance. An intensive measurement campaign was conducted at Xi&rsquo;an, China, from December 2012 to January 2013 to investigate the sources and physicochemical characteristics of refractory BC (rBC) and its direct radiative forcing at the surface. The overall average rBC concentration for the campaign was 8.0 &plusmn; 7.1 &mu;g m 3. Source apportionment based on positive matrix factorization showed that traffic was the dominant rBC source (46.0%), followed by coal burning (33.9%) and biomass burning (20.1%). The rBC mass size distributions were monomodal and lognormal with larger mass median diameters for coal burning source (215 nm) compared with the traffic source (189 nm). Coal burning rBC was more strongly associated with sulfate than traffic rBC, suggesting a higher cloud condensation nuclei activity. The slope of a robust linear regression between rBC and carbon monoxide (CO) for all samples was 5.9 &mu;g m 3 ppm 1, and the slope for the coal burning source (4.5 &mu;g m 3 ppm 1) was larger than that for the traffic source (2.7 &mu;g m 3 ppm 1). The net rBC emission during winter of 2009 was estimated to be 4.5 Gg based on the relationship between rBC and CO. A Tropospheric Ultraviolet and Visible radiation model showed that the average daytime value for the clear-sky direct radiative forcing due to rBC from 23 December 2012 to 31 January 2013 was 47.7 &plusmn; 28.9 W m 2, which amounted to an average of 45.7% of the total surface atmospheric aerosol forcing.</p

Impacts of short-term mitigation measures on PM2.5 and radiative effects: a case study at a regional background site near Beijing, China

Measurements at a background site near Beijing showed that pollution controls implemented during the 19th National Congress of the Communist Party of China (NC-CPC) were effective in reducing PM2.5. Mass concentrations of PM2.5 and its major chemical components were 20.6%-43.1% lower during the NCCPC-control period compared with a non-control period, and differences were greater on days with stable meteorological conditions. A receptor model showed that PM2.5 from traffic-related emissions, biomass burning, industrial processes, and mineral dust was 38.5%-77.8% lower during the NCCPC-control versus non-control period, but differences in PM2.5 from coal burning were small, and secondary sources were higher during the NCCPC-control period. During one pollution episode in the non-control period, secondary sources dominated, and the WRF-Chem model showed that the Beijing-Tianjin-Hebei (BTH) region contributed 73.6% of PM2.5 mass. A second pollution episode was linked to biomass burning, and BTH contributed 46.9% of PM2.5 mass. Calculations based on Interagency Monitoring of Protected Visual Environments (IMPROVE) algorithms showed that organic matter was the largest contributor to light extinction during the non-control period whereas NH4NO3 was the main contributor during the NCCPC. The Tropospheric Ultraviolet and Visible radiation model showed that the average direct radiative forcing (DRF) values at the Earth's surface were -14.0 and -19.3 W m(-2) during the NCCPC-control and non-control periods, respectively, and the DRF for the individual PM2.5 components were 22.7%-46.7% lower during the NCCPC. The information and dataset from this study will be useful for developing air pollution control strategies in the BTH region and for understanding associated aerosol radiative effects

Seasonal variation and four-year trend of black carbon in the Midwest China: The analysis of the ambient measurement and WRF-Chemmodeling

In-situ measurement of black carbon (BC) concentration from September 2003 to August 2007 in the Xi'an City at the Guanzhong Basin located in the mid-western China (the Guanzhong Basin) was analyzed. A regional dynamics and aerosol model (WRF-Chem) was used to quantify the impacts of local emission, meteorological conditions, and regional atmospheric transport on seasonal variation of BC concentration at the Guanzhong Basin. The results show that the regional prevailing winds at the Guanzhong Basin were unfavorable for the horizontal transport. The mean wind speeds ranged from 1.0 m/s to 1.9 m/s. During winter, the wind at the Guanzhong Basin was very weak (∼1.0 m/s). During spring and autumn, there was a wind convergent zone at the Guanzhong Basin, constraining the BC concentrations inside the Guanzhong Basin. As a result, the BC concentrations were persistently high at the Guanzhong Basin. In addition to the high background concentrations, there was a strong seasonal variation, with a maximum in winter (winter maximum) and a minimum in summer (summer minimum), with the maximum of the mean concentration of 30 μg m−3 in 2003–2004 winter, and the minimum of 5 μg m−3 in 2004 summer. The model sensitivity study shows that the seasonal variation of BC concentration was largely due to the seasonal variation of BC emission, especially during winter with the maximum of BC emission. A strong annual decrease trend of the BC concentration was found from 2004 to 2007. It is interesting to note that the decrease of the BC concentration only occurred in winter. For example, the winter maximum was 20 μg m−3 in 2003, and reduced to 11 μg m−3 in 2006, with about 50% decrease. In contrast, the summer minimum was 10 μg m−3 in 2004 and 9 μg m−3 in 2007, with only 10% decrease. This study suggests that the rapid decrease in the winter maximum was mainly due to the reduction of the BC emission in winter, implying the effective winter emission control at the Guanzhong Basin