Characterizing winter-time brown carbon: Insights into chemical and light-absorption properties in residential and traffic environments

Luis M F Barreira; Minna Aurela; Sanna Saarikoski; Delun Li; Kimmo Teinilä; Aki Virkkula; Jarkko V Niemi; H E Manninen; Liisa Pirjola; Tuukka Petäjä; Topi Rönkkö; Hilkka Timonen

doi:10.1016/j.scitotenv.2024.177089

Characterizing winter-time brown carbon: Insights into chemical and light-absorption properties in residential and traffic environments

Sci Total Environ. 2024 Dec 10:955:177089. doi: 10.1016/j.scitotenv.2024.177089. Epub 2024 Oct 31.

Authors

Affiliations

¹ Atmospheric Composition Research, Finnish Meteorological Institute, 00101 Helsinki, Finland.
² Helsinki Region Environmental Services Authority, 00066 Helsinki, Finland.
³ Department of Automotive and Mechanical Engineering, Metropolia University of Applied Sciences, 01600 Vantaa, Finland; Institute for Atmospheric and Earth System Research (INAR), Faculty of Science, University of Helsinki, Finland.
⁴ Institute for Atmospheric and Earth System Research (INAR), Faculty of Science, University of Helsinki, Finland.
⁵ Aerosol Physics Laboratory, Physics Unit, Faculty of Engineering and Natural Sciences, Tampere University, 33014 Tampere, Finland.
⁶ Atmospheric Composition Research, Finnish Meteorological Institute, 00101 Helsinki, Finland. Electronic address: Hilkka.Timonen@fmi.fi.

PMID: 39477102
DOI: 10.1016/j.scitotenv.2024.177089

Abstract

Brown carbon (BrC) is an organic aerosol (OA) component that possesses light-absorbing properties in the UV-Vis spectrum, impacting climate. However, the current understanding of climate repercussions stemming from BrC emissions remains insufficient due to a lack of comprehensive knowledge regarding its chemical makeup, light-absorption, and the role of atmospheric aging in shaping BrC properties. This study investigates BrC in PM₁ (particulate matter <1μm) during winter in Helsinki, Finland, in a street canyon and a residential area with wood combustion. The aim was to ascertain BrC sources, chemical composition, and contribution to UV-Vis light absorption. The study utilized a seven-wavelength aethalometer (AE33) to measure black carbon (BC) and BrC light absorptions, and a soot particle aerosol mass spectrometer (SP-AMS) to determine OA composition. An OA source apportionment using positive matrix factorization followed by a multiple regression analysis between BrC absorption and each factor was performed to determine the mass absorption coefficients of BrC (MAC_BrC) and light absorption contributions of distinct sources across 370-660 nm wavelengths. The BrC UV-Vis absorption relative to the one of BC was higher at 370 nm, with a median contribution of 20.1 % in the residential area and 18.2 % at the traffic site. Residential BrC absorption showed sporadic peaks, while street canyon absorption was lower but consistent. MAC_BrC was higher for biomass burning organic aerosol but still significant for long-range transported (LRT) and traffic-related aerosols. Hydrocarbon-like organic aerosol exhibited higher MAC_BrC at 470 nm than at 370 nm. Combined with particulate mass concentrations, biomass burning and LRT contributed the most to light absorption. Uncertainties regarding MAC_BrC were evaluated. The chemical composition analysis revealed stronger correlations between BrC absorption and SP-AMS-measured ions, especially in residential areas and for polycyclic aromatic hydrocarbons and oxidized aromatics. The study emphasizes the importance of anthropogenic sources in BrC light absorption.

Keywords: Brown carbon; Chemical properties; Light absorption; Northern latitudes; Source apportionment; Wintertime air quality.