Large-scale wildfires are essential sources of black carbon (BC) and brown carbon (BrC), affecting aerosol-induced radiative forcing. This study investigated the impact of two wildfire plumes (Plume 1 and 2) transported to Moscow on the optical properties of BC and BrC during August 2022. During the wildfires, the total light absorption at 370 nm (b(abs_370nm)) increased 2.3-3.4 times relative to background (17.30 +/- 13.98 Mm(-)(1)), and the BrC contribution to total absorption increased from 14 % to 42-48 %. BrC was further partitioned into primary (BrCPri) and secondary (BrCSec) components. Biomass burning accounted for similar to 83-90 % of BrCPri during the wildfires. The b(abs_370nm) of BrCPri increased 5.6 times in Plume 1 and 11.5 times in Plume 2, due to the higher prevalence of peat combustion in Plume 2. b(abs_370nm) of BrCSec increased 8.3-9.6 times, driven by aqueous-phase processing, as evidenced by strong correlations between aerosol liquid water content and b(abs_370nm) of BrCSec. Daytime b(abs_370nm) of BrCSec increased 7.6 times in Plume 1 but only 3.6 times in Plume 2, due to more extensive photobleaching, as indicated by negative correlations with oxidant concentrations and longer transport times. The radiative forcing of BrCPri relative to BC increased 1.8 times in Plume 1 and Plume 2. In contrast, this increase for BrCSec was 3.4 times in Plume 1 but only 2.3 times in Plume 2, due to differences in chemical processes, which may result in higher uncertainty in its radiative forcing. Future work should prioritize elucidating both the emissions and atmospheric processes to better quantify wildfire-derived BrC and its radiative forcing.

Light-absorbing carbonaceous aerosols primarily comprise black carbon (BC) and brown carbon (BrC), and they play a key role in atmospheric radiative forcing and global climate. Here, we present the light absorption, potential sources, and health risks of BC and BrC during the prescribed burning season at an urban background site in Brisbane based on the measurements with a seven-wavelength aethalometer. The enhancements in light absorption at 880 nm were potentially governed by the transport of prescribed burning emissions. Source apportionment results revealed that fossil-fuel (FF) combustion contributed more to the total equivalent BC (eBC) (67%) over the entire measurement period as compared to biomass burning (BB). The percentages of secondary BrC to BrC for BB- and FF-dominated periods were 60% and 21%, respectively, indicating the greater potential of BB emissions to form secondary BrC compared to FF emissions. The diurnal trend showed that the peaks of secondary BrC occurred at nighttime with high relative humidity, implying that the formation of secondary BrC was potentially associated with aqueous reactions. Potential source contribution function (PSCF) results suggested that air masses originating from southern and northern Brisbane were the potential pollution sources, where BB and traffic emissions were dominant. In addition, the health risks of eBC (based on equivalent numbers of passively smoked cigarettes) remarkably increased for periods with elevated eBC emissions, potentially originating from prescribed burns. These findings contribute to our understanding of the impact of BB on the light absorption properties of BC and BrC and could serve as a reference for government officials when performing prescribed burns with reduced environmental and health effects.

To investigate the seasonal variation of black carbon (BC) and brown carbon (BrC) light absorption at an urban site in Xi'an, China, an annual measurement was conducted by using a 7-wavelengths Aethalometer (model AE33). The results showed the aerosol absorptions were observed approximately 5-8 times greater in winter (395 Mm(-1) at 370 nm and 99 Mm(-1) at 880 nm, respectively) than those in autumn (49 Mm(-1) at 370 nm and 18 Mm(-1) at 880 nm, respectively). BC was the dominant light absorbing carbonaceous component at all wavelengths (from 370 nm to 950 nm). BrC absorption (370 nm) maximized during winter with 41% of the total aerosol absorption, and was lower in autumn (16%). The light absorption contributions of primary BrC (BrCpri) were higher than that of secondary BrC (BrCsec) in four seasons, with more than 67% of total BrC light absorption. The seasonal absorption Angstrom exponents (AAEs) of BrC, BrCpri, and BrCsec were directly derived with the highest values (3.91, 3.69, and 4.94, respectively) in wintertime. The BrCpri contributed much higher solar absorptions percentage to BC than BrCsec. The results underlined the primary emissions of urban BrCpri and BC, implying that the strategies of energy efficiency enhancement and energy structure reformation will be very important in reducing primary emissions in China. Such investigations should be conducted in other developing countries with severe air pollution. (c) 2020 Published by Elsevier B.V. on behalf of International Association for Gondwana Research.