The light absorption enhancement (E-abs) of black carbon (BC) coated with non-BC materials is crucial in the assessment of radiative forcing, yet its evolution during photochemical aging of plumes from biomass burning, the globe's largest source of BC, remains poorly understood. In this study, plumes from open burning of corn straw were introduced into a smog chamber to explore the evolution of E-abs during photochemical aging. The light absorption of BC was measured with and without coating materials by using a thermodenuder, while the size distributions of aerosols and composition of BC coating materials were also monitored. E-abs was found to increase initially, and then decrease with an overall downward trend. The lensing effect dominated in E-abs at 520 nm, with an estimated contribution percentages of 47.5%-94.5%, which is far greater than light absorption of coated brown carbon (BrC). The effects of thickening and chemical composition changes of the coating materials on E-abs were evaluated through comparing measured E-abs with that calculated by the Mie theory. After OH exposure of 1 x 10(10) molecules cm(-3) s, the thickening of coating materials led to an E-abs increase by 3.2% +/- 1.6%, while the chemical composition changes or photobleaching induced an E-abs decrease by 4.7% +/- 0.6%. Simple forcing estimates indicate that coated BC aerosols exhibit warming effects that were reduced after aging. The oxidation of light-absorbing CxHy compounds, such as polycyclic aromatic hydrocarbons (PAHs), to CxHyO and CxHyO>1 compounds in coating materials may be responsible for the photobleaching of coated BrC. Plain Language Summary Understanding how black carbon (BC) coated with non-BC materials affects light absorption is crucial for assessing its impact on the Earth's climate. However, there is limited knowledge about how this process changes when BC, particularly from biomass burning, is exposed to light. Biomass burning is a significant global source of BC. This study investigated the changes in light absorption of BC from burning corn straw as it aged in a controlled environment. We measured the light absorption of BC with and without its coating materials. Our results showed that the main cause of increased light absorption was the lensing effect of the coating materials, which was more significant than the light absorption by the coating materials themselves. We also discovered that as the coating materials thickened, BC absorbed more light. However, changes in the chemical composition of the coating materials led to a decrease in total absorption. These findings suggest that while coated BC initially has a warming effect on the climate, this effect diminished as the BC ages. The decrease is likely due to the breakdown of light-absorbing compounds in the coating materials, such as polycyclic aromatic hydrocarbons (PAHs).

High uncertainty in optical properties of black carbon (BC) involving heterogeneous chemistry has recently attracted increasing attention in the field of atmospheric climatology. To fill the gap in BC optical knowledge so as to estimate more accurate climate effects and serve the response to global warming, it is beneficial to conduct site-level studies on BC light absorption enhancement (E-abs) characteristics. Real-time surface gas and particulate pollutant observations during the summer and winter over Wuhan were utilized for the analysis of E-abs simulated by minimum R squared (MRS), considering two distinct atmospheric conditions (2015 and 2017). In general, differences in aerosol emissions led to E-abs differential behaviors. The summer average of E-abs (1.92 +/- 0.55) in 2015 was higher than the winter average (1.27 +/- 0.42), while the average (1.11 +/- 0.20) in 2017 summer was lower than that (1.67 +/- 0.69) in winter. E-abs and R-BC (representing the mass ratio of non-refractory constituents to elemental carbon) constraints suggest that E-abs increased with the increase in R-BC under the ambient condition enriched by secondary inorganic aerosol (SIA), with a maximum growth rate of 70.6% in 2015 summer. However, E-abs demonstrated a negative trend against R-BC in 2017 winter due to the more complicated mixing state. The result arose from the opposite impact of hygroscopic SIA and absorbing OC/irregular distributed coatings on amplifying the light absorbency of BC. Furthermore, sensitivity analysis revealed a robust positive correlation (R > 0.9) between aerosol chemical compositions (including sulfate, nitrate, ammonium and secondary organic carbon), which could be significantly perturbed by only a small fraction of absorbing materials or restructuring BC through gaps filling. The above findings not only deepen the understanding of BC, but also provide useful information for the scientific decision-making in government to mitigate particulate pollution and obtain more precise BC radiative forcing.

To elucidate the variations in mass concentrations of organic carbon (OC) and black carbon (BC) in PM2s and their light absorption characteristics in Lanzhou, we conducted one-year online measurements by using a newly developed total carbon analyzer (TCA08) coupled with an aethalometer (AE33) from July 2018 to July 2019. The mean OC and BC concen-trations were 6.4 +/- 4.4 and 2.0 +/- 1.3 pg/m3, respectively. Clear seasonal variations were observed for both components, with winter having the highest concentrations, followed by autumn, spring, and summer. The diurnal variations of OC and BC concentrations were sim-ilar throughout the year, with daily two peaks occurring in the morning and evening, respec-tively. A relatively low OC/BC ratio (3.3 +/- 1.2, n = 345) were observed, indicating that fossil fuel combustion was the primary source of the carbonaceous components. This is further substantiated by relatively low biomass burning contribution (fbiomass: 27.1% +/- 11.3%) to BC using aethalometer based measurement though f biomass value which increased significantly in winter (41.6% +/- 5.7%). We estimated a considerable brown carbon (BrC) contribution to the total absorption coefficient (babs) at 370 nm (yearly average of 30.8% +/- 11.1%), with a win-ter maximum of 44.2% +/- 4.1% and a summer minimum of 19.2% +/- 4.2%. Calculation of the wavelength dependence of total babs revealed an annual mean AAE370-520 value of 4.2 +/- 0.5, with slightly higher values in spring and winter. The mass absorption cross- of BrC also exhibited higher values in winter, with an annual mean of 5.4 +/- 1.9 m2middotg-1 , reflecting the impact of emissions from increased biomass burning on BrC concentrations.(c) 2022 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

South and Southeast Asia (SSA) emitted black carbon (BC) exerts potential effects on glacier and snow melting and regional climate change in the Tibetan Plateau. In this study, online BC measurements were conducted for 1 year at a remote village located at the terminus of the Mingyong Glacier below the Meili Snow Mountains. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) was used to investigate the contribution and potential effect of SSA -emitted BC. In addition, variations in the light absorption characteristics of BC and brown carbon (BrC) were examined. The results indicated that the annual mean concentration of BC was 415 +/- 372 ngm(-3) , with the highest concentration observed in April (monthly mean: 930 +/- 484 ngm(-3) ). BC exhibited a similar diurnal variation throughout the year, with two peaks observed in the morning (from 8:00 to 9:00 AM) and in the afternoon (from 4:00 to 5:00 PM), with even lower values at nighttime. At a short wavelength of 370 nm, the absorption coefficient ( b abs ) reached its maximum value, and the majority of b abs values were < 20 Mm(-1) , indicating that the atmosphere was not overloaded with BC. At the same wavelength, BrC substantially contributed to b abs , with an annual mean of 25.2 % +/- 12.8 %. SSA was the largest contributor of BC (annual mean: 51.1 %) in the study area, particularly in spring (65.6 %). However, its contributions reached 20.2 % in summer, indicating non -negligible emissions from activities in other regions. In the atmosphere, the SSA BC -induced radiative forcing (RF) over the study region was positive. While at the near surface, the RF exhibited a significant seasonal variation, with the larger RF values occurring in winter and spring. Overall, our findings highlight the importance of controlling BC emissions from SSA to protect the Tibetan Plateau against pollution -related glacier and snow cover melting.

Black carbon (BC) is a distinct type of carbonaceous aerosol that has a significant impact on the environment, human health, and climate. A non-BC material coating on BC can alter the mixing state of the BC particles, which considerably enhances the mass absorption efficiency of BC by directing more energy toward the BC cores (lensing effect). A lot of methods have been reported for quantifying the enhancement factor (Eabs), with diverse results. However, to the best of our knowledge, a comprehensive review specific to the quantification methods for Eabs has not been systematically performed, which is unfavorable for the evaluation of obtained results and subsequent radiative forcing. In this review, quantification methods are divided into two broad categories, direct and indirect, depending on whether experimental removal of the coating layer from an aged carbonaceous particle is required. The direct methods described include thermal peeling, solvent dissolution, and optical virtual exfoliation, while the indirect methods include intercept-linear regression fitting, minimum R squared, numerical simulation, and empirical value. We summarized the principles, procedures, virtues, and limitations of the major Eabs quantification methods and analyzed the current problems in the determination of Eabs. We pointed out what breakthroughs are needed to improve or innovate Eabs quantification methods, particularly regarding the need to avoid the influence of brown carbon, develop a broadband Eabs quantification scheme, quantify the Eabs values for the emissions of low-efficiency combustions, measure the Eabs of particles in a highhumidity environment, design a real-time monitor of Eabs by a proper combination of mature techniques, and make more use of artificial intelligence for better Eabs quantification. This review deepens the understanding of Eabs quantification methods and benefits the estimation of the contribution of BC to radiative forcing using climate models.

Reducing the uncertainty in aerosol radiative forcing requires a comprehensive understanding of the factors affecting black carbon (BC) light absorption. In this study, the characteristics and influencing factors of light absorption enhancement (Eabs) of refractory BC (rBC) were investigated by conducting intensive measurements at an urban site in northwest China during the early summer of 2018. On average, the absorption of rBC was enhanced by 34% as a result of the internal mixing of rBC with other aerosol components. Secondary inorganic aerosols (SIAs) were found to have considerable effects on the Eabs of rBC. The Eabs showed a robust linear relationship with the bulk nitrate/rBC mass ratio in fine particles, with an increase of 3% per nitrate/rBC ratio unit. A notable increase in Eabs from dusk to the next morning was observed, in accordance with the diurnal variations in nitrate and sulfate, indicating the excellent contribution of non-photochemical formation of SIAs to Eabs. This fact was further supported by the positive correlation of the nitrate/rBC and sulfate/rBC ratios with relative humidity (RH) rather than photochemical indicators. This study indicates that the aqueous and/or heterogeneous formation of SIAs is likely the dominant aging pathway leading to the high Eabs of rBC.

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.

Sichuan Basin is encircled by high mountains and plateaus with the heights ranging from 1 km to 3 km, and is one of the most polluted regions in China. However, the dominant chemical species and light absorption properties of aerosol particles is still not clear in rural areas. Chemical composition in PM1 (airborne particulate matter with an aerodynamic diameter less than 1 mu m) and light-absorbing properties were determined in Chengdu (urban) and Sanbacun (rural) in western Sichuan Basin (WSB), Southwest China. Carbonaceous aerosols and secondary inorganic ions (NH4+, NO3- and SO42-) dominate PM1 pollution, contributing more than 85% to PM1 mass at WSB. The mean concentrations of organic and elemental carbon (OC, EC), K+ and Cl- are 19.69 mu g m(-3), 8.00 mu g m(-3), 1.32 mu g m(-3),1.16 mu g m(-3) at the rural site, which are 26.2%, 65.3%, 34.7% and 48.7% higher than those at the urban site, respectively. BrC (brown carbon) light absorption coefficient at 405 nm is 63.90 +/- 27.81 M m(-1) at the rural site, contributing more than half of total absorption, which is about five times higher than that at urban site (10.43 +/- 4.74 M m(-1)). Compared with secondary OC, rural BrC light absorption more depends on primary OC from biomass and coal burning. The rural MAE(Brc) (BrC mass absorption efficiency) at 405 nm ranges from 0.6 to 5.1 m(2) g(-1) with mean value of 3.5 +/- 0.8 m(2) g(-1), which is about three times higher than the urban site. (C) 2021 Elsevier Ltd. All rights reserved.

The Indo-Gangetic Plain (IGP) is a major regional and global emitter of atmospheric pollutants, which adversely affect surrounding areas such as the Himalayas. We present a comprehensive dataset on carbonaceous aerosol (CA) composition, radiocarbon (D14C) -based source apportionment, and light absorption of total suspended particle (TSP) samples collected over a 3--year period from high-altitude Jomsom in the central Himalayas. The 3-year mean TSP, organic carbon (OC), and elemental carbon (EC) concentrations were 92.0 +/- 28.6, 9.74 +/- 6.31, and 2.02 +/- 1.35 lg m-3, respectively, with the highest concentrations observed during the pre-monsoon season, followed by the post-monsoon, winter, and monsoon seasons. The D14C analysis revealed that the contribution of fossil fuel combustion (ffossil) to EC was 47.9% +/- 11.5%, which is consistent with observations in urban and remote regions in South Asia and attests that EC likely arrives in Jomsom from upwind IGP sources via long-range transport. In addition, the lowest ffossil (38.7% +/- 13.3%) was observed in winter, indicating large contributions in this season from local biomass burning. The mass absorption cross- of EC (MACEC: 8.27 +/- 1.76 m2/g) and watersoluble organic carbon (MACWSOC: 0.98 +/- 0.45 m2/g) were slightly higher and lower than those reported in urban regions, respectively, indicating that CA undergo an aging process. Organic aerosol coating during transport and variation of biomass burning probably led to the seasonal variation in MAC of two components. Overall, WSOC contributed considerably to the light absorption (11.1% +/- 4.23%) of EC. The findings suggest that to protect glaciers of the Himalayas from pollution-related melting, it is essential to mitigate emissions from the IGP.(c) 2022 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Brown carbon (BrC) represents not only a major component of haze pollution but also a non-negligible contributor to positive radiative forcing, making it a key species for coordinating air quality and climate policies. In China, field observations on BrC remain limited given the highly variable emission sources and meteorological conditions across different regions. Here we focused on the optical properties of BrC in a distinct but rarely studied megacity in Northeast China, which is within a major agricultural region and experiences extremely cold winter. Agricultural fires were evident in April of 2021 and the fall of 2020, although open burning was strictly prohibited. Such emissions enhanced BrC's mass absorption efficiency at 365 nm (MAE365), more efficiently by the fall fires which were inferred to have relatively high combustion efficiencies (CE). After taking CE into consideration, the relationships between MAE365 and the levoglucosan to organic carbon ratio (a measure of the significance of agricultural fire influence) roughly converged for the fire episodes in different seasons, including those identified in February and March of 2019 by a previous campaign. Agricultural fires also influenced the determination of absorption & ANGS;ngstrom exponent (AAE), by resulting in non-linearity for BrC's absorption spectra shown on ln-ln scale. Based on three indicators developed by this study, the non-linearity was inferred to be caused by similar chromophores although the fires were characterized by various CE levels in different seasons. In addition, for the samples without significant influence of open burning, coal combustion emissions were identified as the dominant influencing factor for MAE365, whereas none solid link was found between the solution-based AAE and aerosol source.