Size-resolved light-absorbing organic carbon and organic molecular markers in Nanjing, east China: Seasonal variations and sources

Wei Feng; Zhijuan Shao; Qin'geng Wang; Mingjie Xie

doi:10.1016/j.envpol.2023.122006

Size-resolved light-absorbing organic carbon and organic molecular markers in Nanjing, east China: Seasonal variations and sources

Environ Pollut. 2023 Sep 1:332:122006. doi: 10.1016/j.envpol.2023.122006. Epub 2023 Jun 9.

Authors

Wei Feng¹, Zhijuan Shao², Qin'geng Wang³, Mingjie Xie⁴

Affiliations

¹ Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, 219 Ningliu Road, Nanjing, 210044, China.
² School of Environment Science and Engineering, Suzhou University of Science and Technology ShiHu Campus, 99 Xuefu Road, Suzhou, 215009, China.
³ State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China.
⁴ Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, 219 Ningliu Road, Nanjing, 210044, China. Electronic address: mingjie.xie@nuist.edu.cn.

PMID: 37302787
DOI: 10.1016/j.envpol.2023.122006

Abstract

Owing to the potential influence of light-absorbing organic carbon (OC), also termed "brown carbon" (BrC), on the planetary radiation budget, many studies have focused on its absorption in single-sized ranges of particulate matter (PM). However, the size distribution and organic tracer-based source apportionment of BrC absorption have not been extensively investigated. In this study, size-resolved PM samples were collected using multi-stage impactors from eastern Nanjing during each season in 2017. The light absorption of methanol-extractable OC at 365 nm (Abs₃₆₅, Mm^-1) was determined using spectrophotometry, and a series of organic molecular markers (OMMs) was measured using a gas chromatography-mass spectrometer. Fine PM with an aerodynamic diameter <2.1 μm (PM_2.1) dominated Abs₃₆₅ (79.8 ± 10.4%) of the total size ranges with maxima and minima in winter and summer, respectively. The distributions of Abs₃₆₅ shifted to larger PM sizes from winter to spring and summer due to lower primary emissions and increased BrC chromophores in dust. Except for low-volatility (p^o,*_L < 10^-10 atm) polycyclic aromatic hydrocarbons (PAHs), the non-polar OMMs, including n-alkanes, PAHs, oxygenated PAHs, and steranes, showed a bimodal distribution pattern. Secondary products of biogenic precursors and biomass burning tracers presented a unimodal distribution peaking at 0.4-0.7 μm, while sugar alcohols and saccharides were enriched in coarse PM. Their seasonal variations in average concentrations reflected intense photochemical reactions in summer, more biomass burning emissions in winter, and stronger microbial activity in spring and summer. Positive matrix factorization was used for the source apportionment of Abs₃₆₅ in fine and coarse PM samples. Biomass burning contributed an average of 53.9% to the Abs₃₆₅ of PM_2.1 extracts. The Abs₃₆₅ of coarse PM extracts was associated with various dust-related sources where the aging processes of aerosol organics could occur.

Keywords: Light absorption; Organic molecular marker; Seasonal variation; Size distribution; Source apportionment.

MeSH terms

Aerosols / analysis
Air Pollutants* / analysis
Carbon / analysis
China
Dust
Environmental Monitoring
Organic Chemicals / analysis
Particulate Matter / analysis
Polycyclic Aromatic Hydrocarbons* / analysis
Seasons

Substances

Air Pollutants
Carbon
Particulate Matter
Dust
Organic Chemicals
Aerosols
Polycyclic Aromatic Hydrocarbons