Seasonal variability of nitroaromatic compounds in ambient aerosols: Mass size distribution, possible sources and contribution to water-soluble brown carbon light absorption

Sanja Frka; Martin Šala; Helena Brodnik; Bogdan Štefane; Ana Kroflič; Irena Grgić

doi:10.1016/j.chemosphere.2022.134381

Seasonal variability of nitroaromatic compounds in ambient aerosols: Mass size distribution, possible sources and contribution to water-soluble brown carbon light absorption

Chemosphere. 2022 Jul:299:134381. doi: 10.1016/j.chemosphere.2022.134381. Epub 2022 Mar 19.

Authors

Sanja Frka¹, Martin Šala², Helena Brodnik³, Bogdan Štefane³, Ana Kroflič², Irena Grgić⁴

Affiliations

¹ Division for Marine and Environmental Research, Ruđer Bošković Institute, 10000, Zagreb, Croatia; Department of Analytical Chemistry, National Institute of Chemistry, 1000, Ljubljana, Slovenia. Electronic address: frka@irb.hr.
² Department of Analytical Chemistry, National Institute of Chemistry, 1000, Ljubljana, Slovenia.
³ Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna Pot 113, 1000, Ljubljana, Slovenia.
⁴ Department of Analytical Chemistry, National Institute of Chemistry, 1000, Ljubljana, Slovenia. Electronic address: irena.grgic@ki.si.

PMID: 35318013
DOI: 10.1016/j.chemosphere.2022.134381

Abstract

Nitroaromatic compounds (NACs) as important constituents of atmospheric humic-like substances (HULIS) and brown carbon (BrC) affect the Earth's climate and pose a serious environmental hazard. We investigated seasonal size-segregated NACs in aerosol samples from the urban background environment in Ljubljana, Slovenia. Total concentrations of twenty NACs in PM_15.6 were on average from 0.51 ng m^-3 (summer) to 109 ng m^-3 (winter), and contributed the most to submicron aerosols (more than 74%). Besides 4-nitrocatechol (4NC) as the prevailing species, methylnitrocatechols (MNCs) and nitrophenols (NPs), we reported on some very rarely mentioned, but also on five novel NACs (i.e., 3H4NBA: 3-hydroxy-4-nitrobenzoic acid, 3MeO4NP: 3-methoxy-4-nitrophenol, 4Et5NC: 4-ethyl-5-nitrocatechol, 3Et5NC: 3-ethyl-5-nitrocatechol and 3MeO5NC: 3-methoxy-5-nitrocatechol). Concentrations of 3MeO5NC, 4Et5NC and 3Et5NC were enhanced during cold seasons, contributing up to 11% to total NAC in winter. In cold season, NAC size distributions were characterized with the peaks in the broader size range of 0.305-1.01 μm (accumulation mode), with 4NC and alkyl-nitrocatechols (∑(M/Et)NC) as the most abundant, followed by 4-nitrosyringol, nitrophenols and nitroguaiacols. In spring, a pronounced peak of ∑(M/Et)NC was observed in the accumulation mode (0.305-0.56 μm) as well as in the coarse one. A strong correlation of all NACs with ∑(M/Et)NC and levoglucosan indicates that primary emissions of wood burning were the most important source of NACs, but their secondary formation (e.g., aqueous-phase at higher ambient RH) in cold season could also be a significant one. In warmer season, NACs may be mostly derived from traffic-related aromatic VOCs. The contribution of NACs to the light absorption of the aqueous extracts was up to 10-times higher (contribution to Abs₃₆₅ up to 31%) than their mass contributions to WSOC (up to 3%) of corresponding size-segregated aerosols, confirming that most of the identified NACs are strong BrC chromophores.

Keywords: Biomass burning; Brown carbon; Nitroaromatic compounds; Size distribution; Water-soluble organic carbon.

MeSH terms

Aerosols / analysis
Air Pollutants* / analysis
Carbon* / analysis
Environmental Monitoring
Humic Substances / analysis
Nitrophenols
Particulate Matter / analysis
Seasons
Water

Substances

Aerosols
Air Pollutants
Humic Substances
Nitrophenols
Particulate Matter
Water
Carbon