[Effect of Biomass Burning on Carbonaceous Aerosol Composition and Light Absorption in Guangxi Regional Background Site].

Carbonaceous aerosols are an important component of fine particulate matter (PM2.5) in the atmosphere, having great impacts on air quality, human health, and the climate. In this study, PM2.5 samples were collected from November 2017 to October 2018 in a background site of Guangxi Province to investigate the potential impacts of biomass burning, an essential source of carbonaceous aerosols, on carbonaceous aerosols. Further, the composition of carbonaceous aerosols, sugar compounds, and the light absorption coefficient (babs) of water-soluble brown carbon (BrC) were also conducted. Considering the effect of the degradation of atmospheric levoglucosan (LG), the concentration of the corrected LG was quantified using the aging of air masses (AAM) index. Then, the contribution of biomass burning (BB) to organic carbon (OC) [BB-OC] was quantified using the corrected LG-derived molecular tracer method combined with the Bayesian mixing model. Here, we further explored the potential sources of water-soluble BrC using correlation analysis. In this research, the mean AAM index was 0.40±0.28 during the study period, indicating that the atmospheric LG had undergone a photochemical degradation process. The characteristic ratio combined with the Bayesian mixing model indicated that the crop straw (i.e., corn, rice, and sugarcane straw) was the dominant biomass fuel type in the Guangxi Region, contributing 22%, 23%, and 18% of OC without the correction of LG and 16%, 21%, and 17% with the corrected LG concentration, respectively. The neglection of LG degradation led to the underestimation of BB-OC, in which the BB-OC values with and without correction were 49.0% and 21.1%, respectively. Here, the annual mean babs of water-soluble BrC was (8.7±10.7) Mm-1, and its main sources were BB, fossil fuel combustion, and vegetation emission.

[High-frequency Evolution of Urban Atmospheric Ammonia and Ammonium and Its Gas-to-Particle Conversion Mechanism in Nanjing City].

In this study, hourly mass concentrations of atmospheric gases (mainly NH3) and secondary inorganic aerosols (mainly NH4+, NO3-, and SO42-) in Nanjing City were continuously measured during the fall of 2018 by an online gas and aerosol chemical component monitor. The dataset was used to investigate the variation characteristics of ambient NH3 and NH4+ during polluted and non-polluted periods, and to explore the potential chemical mechanism during gas-to-particle conversion between NH3 and NH4+. The results show that throughout the sampling period, the mean values (±1σ) of the mass concentrations of NH3 and NH4+ were (15.3±6.7) µg·m-3 and (11.3±7.8) µg·m-3, respectively, and that their diurnal profiles were distinct between pollution and non-pollution periods. Analysis of the potential contribution sources indicated that local contributions exceeded long-range transport as the dominant source of measured NH3 and NH4+, suggesting that urban areas can be hotspots of NH3 emissions. Further in-depth analysis revealed that the process of gas-to-particle conversion was the main driving force with respect to controlling diurnal variations in NH3 and NH4+. Specifically, pollution episodes were characterized by low temperature (7.5-12.5℃) and high humidity (50%-90%) meteorological conditions. These conditions tended to accelerate the reaction rate of gas-to-particle conversion and facilitate the formation of aerosol ammonium, leading to pronounced (NH4)2SO4 and NH4NO3 increases during pollution events. These findings clarify the sources of NH3 in the urban atmosphere and its potential contribution to the formation of particulate matter.