Dey Supriya, Ghosh Pronoy, Rawat Prashant, Choudhary Nikki, Rai Akansha, Meena Rohit, Mandal Tuhin K, Mao Jingying, Jia Shiguo, Rastogi Neeraj, Sharma Sudhir K, Sarkar Sayantan
School of Civil and Environmental Engineering, Indian Institute of Technology (IIT) Mandi, Kamand, Himachal Pradesh 175075, India.
CSIR-National Physical Laboratory (CSIR-NPL), Dr. K.S. Krishnan Road, New Delhi 110012, India.
Sci Total Environ. 2023 Oct 10;894:164872. doi: 10.1016/j.scitotenv.2023.164872. Epub 2023 Jun 19.
This study reports day-night and seasonal variations of aqueous brown carbon (BrC) and constituent humic-like substances (HULIS) (neutral and acidic HULIS: HULIS-n and HULIS-a) from the eastern Indo-Gangetic Plain (IGP) of India during 2019-2020. This is followed by the application of the receptor model positive matrix factorization (PMF) for optical source apportionment of BrC and the use of stable isotopic ratios (δC and δN) to understand atmospheric processing. Nighttime BrC absorption and mass absorption efficiencies (MAE) were enhanced by 40-150 % and 50-190 %, respectively, compared to the daytime across seasons, possibly as a combined effect from daytime photobleaching, dark-phase secondary formation, and increased nighttime emissions. MAE/MAE (i.e., E/E) ratios and Angstrom Exponents revealed that BrC and HULIS-n were relatively more aromatic and conjugated during the biomass burning-dominated periods while BrC and HULIS-a were comprised mostly of non-conjugated aliphatic structures from secondary processes during the photochemistry-dominated summer. The relative radiative forcing of BrC with respect to elemental carbon (EC) was 10-12 % in the post-monsoon and winter in the 300-400 nm range. Optical source apportionment using PMF revealed that BrC absorption at 300, 365 and 420 nm wavelengths in the eastern IGP is mostly from biomass burning (60-75 %), followed by combined marine and fossil fuel-derived sources (24-31 %), and secondary processes (up to 10 %). Source-specific MAEs at 365 nm were estimated to be the highest for the combined marine and fossil fuel source (1.34 m g) followed by biomass burning (0.78 m g) and secondary processing (0.13 m g). Finally, δC and δN isotopic analysis confirmed the importance of summertime photochemistry and wintertime NO-dominated chemistry in constraining BrC characteristics. Overall, the quantitative apportionment of BrC sources and processing reported here can be expected to lead to targeted source-specific measurements and a better understanding of BrC climate forcing in the future.
本研究报告了2019 - 2020年期间印度东部恒河平原（IGP）水体棕色碳（BrC）及其组成的类腐殖质物质（HULIS）（中性和酸性HULIS：HULIS - n和HULIS - a）的昼夜和季节变化。随后应用受体模型正矩阵因子分解（PMF）对BrC进行光生源解析，并利用稳定同位素比率（δC和δN）来了解大气过程。与白天相比，夜间BrC的吸收和质量吸收效率（MAE）在各个季节分别提高了40 - 150%和50 - 190%，这可能是白天光漂白、暗相二次形成以及夜间排放增加的综合作用。MAE/MAE（即E/E）比率和埃指数表明，在以生物质燃烧为主的时期，BrC和HULIS - n相对更具芳香性和共轭性，而在以光化学为主导的夏季，BrC和HULIS - a主要由二次过程中的非共轭脂肪族结构组成。在300 - 400 nm范围内，BrC相对于元素碳（EC）的相对辐射强迫在季风后和冬季为10 - 12%。利用PMF进行光生源解析表明，IGP东部300、365和420 nm波长处的BrC吸收主要来自生物质燃烧（60 - 75%），其次是海洋和化石燃料衍生源的综合贡献（24 - 31%）以及二次过程（高达10%）。在365 nm处，特定源的MAE估计以海洋和化石燃料综合源最高（1.34 m² g⁻¹），其次是生物质燃烧（0.78 m² g⁻¹）和二次过程（0.13 m² g⁻¹）。最后，δC和δN同位素分析证实了夏季光化学和冬季以NO为主的化学过程在限制BrC特征方面的重要性。总体而言，本文报道的BrC来源和过程的定量解析有望在未来实现针对性的特定源测量，并更好地理解BrC的气候强迫作用。
