Synergistic effect in absorption properties of brown carbon and elemental carbon over IGP during weak south-west monsoon

Abstract

Recent ground-based measurements reveal that model-based observations are underestimating absorption properties and direct radiative forcing (DRF) due to carbonaceous species by a factor of 2-3 over South and East Asia. Thus, to better constraint these parameters associated with carbonaceous species, seasonal variability records through ground-based measurements are very essential. In this context, we report herein the absorption properties of water-extractable brown carbon (BrC), elemental carbon (EC), and BrC ? EC and DRF of BrC and BrC ? EC (relative to EC) over the Indo-Gangetic Plain (IGP) during a weak monsoon season [July-September 2015; influenced by El Niño and PDO (Pacific Decadal Oscillation)]. PM 2.5 (particulate matter with aerodynamic diameter B 2.5 lm) samples (n = 31) have been assessed from central IGP location at Kanpur. Absorption coefficient at 365 nm (b abs-365 ) of BrC, EC, and BrC ? EC centers at 3.6, 8.1, and 11.4 Mm -1 , respectively. Strong linear regression correlation (R = 0.8) of b abs-365 of BrC with sea-salt and mineral dust corrected potassium (K þ BB ) indicates biomass burning as the predominant source of BrC over the region in this study. Synergistic effect in b abs of BrC ? EC (relative to that of EC) increases conspicuously (enhanced by a factor varying from 1.05 to 1.21) with an increase in wavelength from UV (365 nm) to visible region (660 nm). DRF (relative to EC) of BrC during monsoon season ranges from 3.9 to 23.8 (13.0 ± 5.0) %, whereas total DRF (BrC ? EC) ranges from 111.0 to 148.2 (126.6 ± 10.0) %. Individual contribution of BrC and EC to total DRF has been estimated as 10 and 79.5%, respectively. The remaining contribution (10.5%) to total DRF has been attributed to synergism in absorption properties (i.e., b abs ) of BrC ? EC.

Brownness of Organics in Anthropogenic Biomass Burning Aerosols over South Asia

“…The absorption of this methanol-soluble OC (considered as BrC absorption) was estimated by 140 using a UV-visible spectrophotometer (LAMBDA 35, PerkinElmer) with a working range of 300 nm to 900 nm and a spectral resolution of 1 nm. The equation shown below was used to estimate the absorption at any given wavelength (Chakrabarty et al, 2023;Sarkar et al, 2019;Satish and Rastogi, 2019;Sarin, 2013, 2014;Bikkina et al, 2020;Boreddy et al, 2021;Choudhary et al, 2017Choudhary et al, , 2018Choudhary et al, , 2021Choudhary et al, , 2022Dasari et al, 2019;Dey et al, 2021;Kirillova 145 et al, 2016;Mukherjee et al, 2020;Rajeev et al, 2022;Rastogi et al, 2021;Rathod et al, 2017;Rana et al, 2020;Shamjad et al, 2016bShamjad et al, , 2018. In equation 1, 𝐴 𝜆 is absorbance at wavelength λ, 𝑉 𝐸𝑥𝑡𝑟𝑎𝑐𝑡 is the volume of solvent extract used 150 (4.5 ml in this study), 𝑉 𝑆𝑎𝑚𝑝𝑙𝑒𝑑 is the volume of air sampled, 𝑓 𝑓𝑖𝑙𝑡𝑒𝑟 𝑎𝑟𝑒𝑎 is the fraction of filter area used for the analysis, and 𝐿 is the optical path length (0.01 m).…”

“…In contrast, the climate implications of light-absorbing organic carbon (OC), termed brown carbon (BrC), have 45 received relatively less attention and are thus less certain (Saleh et al, 2018;Brown et al, 2018;Saleh, 2020). The chemical composition of BrC varies significantly, and consequently its optical properties, as reported across previous studies, span orders of magnitude in the imaginary refractive index (k) values that determine its light absorbing strength (Chakrabarty et al, 2023;Choudhary et al, 2021Choudhary et al, , 2018Choudhary et al, , 2017Dey et al, 2021;Kapoor et al, 2023a;50 Kirillova et al, 2016;Rana et al, 2020;Rathod et al, 2017;Saleh et al, 2018Saleh et al, , 2014Srinivas and Sarin, 2014). Previous studies often measured aged ambient BrC that are weakly absorbing (kBrC,550 <0.01) due to photobleaching (Sumlin et al, 2017), hence some climate impact assessment studies have considered BrC as a weakly or non-absorbing particle (Lee et al, 2010;Sand et al, 2021;Zhang et al, 2020).…”

Field evidence of brown carbon absorption enhancement linked to organic nitrogen formation in Indo-Gangetic Plain

“…The diurnal peaks in WSOC and babs-WS-BrC-365 during evening and early night were coincided with comparatively higher K + (a tracer for biomass burning) 63 and EC https://doi.org/10.26434/chemrxiv-2023-vgxfp ORCID: https://orcid.org/0000-0001-9344-2737 Content not peer-reviewed by ChemRxiv. License: CC BY-NC-ND 4.0 concentrations (a tracer for vehicular emission) (Table S1), [64][65][66] negligible solar flux (Figure 1b) as well as a contracted BLH (Table S2). It is noted that wood (biomass) burning for heating and cooking is a common practice during wintertime, especially during evening, early night and morning time, in the IGP.…”

Estimating Absorption Ångström Exponent of Black Carbon Aerosol by Coupling Multiwavelength Absorption with Chemical Composition

“…A common way to obtain that information is by accounting for the contributions of the other species based on their own known physicochemical properties. For example, sampled aerosols can be heated to a certain temperature (e.g., 250 °C), so that BC light absorption can be obtained as organic species are vaporized. − Similarly, aerosols on filters can be extracted using various solvents (e.g., deionized water or methanol), and then, the optical properties of the solutions can be measured to estimate the light absorption of BrC. − These approaches usually focus on only one light-absorbing material, that is either BC or BrC, because they are designed to eliminate the effects of all other substances.…”