Sources of organic gases and aerosol particles and their roles in nighttime particle growth at a rural forested site in southwest Germany

Song, Junwei; Saathoff, Harald; Jiang, Feng; Gao, Linyu; Zhang, Hengheng; Leisner, Thomas

The composition, sources and chemical transformation of volatile organic compounds (VOCs) and organic aerosol (OA) particles were investigated during July–August 2021 at a rural forested site in southwest Germany. VOCs and semi-volatile OA particles were measured with a proton-transfer-reaction mass spectrometer coupled with a particle inlet (CHARON-PTR-MS). The CHARON-measured OA mass accounted on average for 63 ± 18 % of the total OA mass (4.2 ± 2.8 μg m -3) concurrently measured by an aerosol mass spectrometer (AMS). The total concentrations of measured VOCs ranged from 7.6 to 88.9 ppb with an average of 31.2 ± 13.4 ppb. Positive matrix factorization (PMF) was used to identify major source factors of VOCs and OA. Three factors of oxygenated VOC (OVOC), namely aromatic-OVOCs, biogenic-OVOCs and aged-OVOCs contributed on average 11 % ± 9 %, 37 % ± 29 %, 29 % ± 21 % of total VOC concentrations, respectively. The results of AMS-PMF indicated substantial contributions of oxygenated organic compounds to OA particle mass. Consistently, three secondary OA (SOA) factors determined by CHARON-PMF analysis, namely aromatic-SOA (5 % ± 7 %), daytime-biogenic SOA (17 % ± 17 %), nighttime-biogenic SOA (28 % ± 21 %), showed high contributions to total CHARON-measured OA mass. Nighttime particle growth was observed regularly at this area, which was mainly attributed by the semi-volatile organic compounds and organic nitrates formed from the oxidation of monoterpenes and sesquiterpenes. This study presents major sources, real-time transformations of VOCs and OA, and nighttime particle formation characteristic for central European forested areas.

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Song, Junwei / Saathoff, Harald / Jiang, Feng / et al: Sources of organic gases and aerosol particles and their roles in nighttime particle growth at a rural forested site in southwest Germany. 2023. Copernicus Publications.

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