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Biomass burning can significantly impact the chemical and optical properties of carbonaceous aerosols. Here, the impacts of biomass burning emissions on chemical and optical properties of carbonaceous aerosols were studied during wintertime in a megacity of Nanjing, East China. The high abundance of biomass burning tracers such as levoglucosan (lev), mannosan (man), galactosan (gal) and non-sea-salt potassium (nss-K+) was found during the studied period with the concentration ranges of 22.4-1476ngm-3, 2.1-56.2ngm-3, 1.4-32.2ngm-3, and 0.2-3.8μgm-3, respectively. Backward air mass origin analysis, potential emission sensitivity of element carbon (EC), and MODIS fire spot information indicated that the elevations of the carbonaceous aerosols were due to the transported biomass-burning aerosols from Southeast China. The characteristic mass ratio maps of lev/man and lev/nss-K+ suggested that the biomass fuels were mainly crop residuals. Furthermore, the strong correlation (p<0.01) between biomass burning tracers (e.g. lev) and light absorption coefficient (babs) for water soluble organic carbon (WSOC) revealed that biomass burning emissions played a significant role in the light-absorption properties of carbonaceous aerosols. The solar energy absorption due to water-soluble brown carbon (BrC) and EC was estimated by the calculation-based on measured light-absorbing parameters and the simulation-based on a radiative transfer model (RRTMG_SW). The solar energy absorption of water-soluble BrC in short wavelengths (300-400nm) was 0.8±0.4 (0.2-2.3)Wm-2 from the calculation-based and 1.2±0.5 (0.3-1.9)Wm-2 from the RRTMG_SW model. The absorption capacity of water-soluble BrC accounted for about 20-30% of the total absorption of EC aerosols. The solar energy absorption of WSOC due to biomass burning was estimated as 0.2±0.1 (0.0-0.9)Wm-2. Potential Source Contribution Function model simulations showed that the solar energy absorption induced by WSOC and EC aerosols was mostly due to the regional transported carbonaceous aerosols from the source regions such as southeast China. Our results illustrate the importance of the absorbing water-soluble brown carbon aerosols in trapping additional solar energy in the low-level atmosphere, heating the surface and inhibiting the energy from escaping the atmosphere. The regional transported biomass burning emissions may significantly impact the chemical and optical properties of carbonaceous aerosols in the polluted atmosphere. [ABSTRACT FROM AUTHOR]

The interpretation of tropospheric cloud formation rests on understanding the sources and processes affecting aerosol constituents of the atmosphere that are preserved in cloudwater. However, this challenge is difficult to be quantitatively addressed based on the sole use of bulk chemical properties. Nitrogenous aerosols, mainly ammonium (NH4+) and nitrate (NO3-), play an important role in tropospheric cloud formation. Here we collected cloudwater samples at the summit of Mt. Tai (1545 m above sea level) in Eastern China during a long-lasting biomass burning (BB) event, and measured for the first time the isotopic compositions (mean ± 1σ) of cloudwater nitrogen species (δ15N-NH4+ = -6.53 ± 4.96‰, δ15N-NO3- = -2.35 ± 2.00‰, δ18O-NO3- = 57.80 ± 4.23‰), allowing insights into their sources and potential transformation mechanism within the clouds. Large contributions of BB to the cloudwater NH4+ (32.9 ± 4.6%) and NO3- (28.2 ± 2.7%) inventories were confirmed through a Bayesian isotopic mixing model, coupled with our newly-developed computational quantum chemistry module. Despite an overall reduction in total anthropogenic NOx emission due to effective emission control actions and stricter emission standards for vehicles, the observed cloud δ15N-NO3- values suggest that NOx emissions from transportation may have exceeded emissions from coal combustion. δ18O-NO3- values imply that the reaction of OH with NO2 is the dominant pathway of NO3- formation (57 ± 11%), yet the contribution of heterogeneous hydrolysis of dinitrogen pentoxide was almost as important (43 ± 11%). [ABSTRACT FROM AUTHOR]