Preprints
https://doi.org/10.5194/acp-2022-467
https://doi.org/10.5194/acp-2022-467
 
02 Aug 2022
02 Aug 2022
Status: this preprint is currently under review for the journal ACP.

Characterization the properties of VOCs and submicron organic aerosol at a street canyon environment

Sanna Saarikoski1, Heidi Hellén1, Arnaud P. Praplan1, Simon Schallhart1, Petri Clusius2, Jarkko V. Niemi3, Anu Kousa3, Toni Tykkä1, Rostislav Kouznetsov1, Minna Aurela1, Laura Salo4, Topi Rönkkö4, Luis M. F. Barreira1, Liisa Pirjola2,5, and Hilkka Timonen1 Sanna Saarikoski et al.
  • 1Atmospheric composition research, Finnish Meteorological Institute, Helsinki, 00101, Finland
  • 2Institute for Atmospheric and Earth Systems Research, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland
  • 3Helsinki Region Environmental Services Authority HSY, Helsinki, 00066, Finland
  • 4Aerosol Physics Laboratory, Physics Unit, Tampere University, Tampere, 33014, Finland
  • 5Department of Automotive and Mechanical Engineering, Metropolia University of Applied Sciences, P.O. Box 4071, 01600, Vantaa, Finland

Abstract. Urban air consists of a complex mixture of gaseous and particulate species from anthropogenic and biogenic sources that are further processed in the atmosphere. This study investigated the features and sources of volatile organic compounds (VOCs) and submicron organic aerosol (OA) at a street canyon in Helsinki, Finland in late summer. The main anthropogenic VOCs (aVOCs) and biogenic VOCs (bVOCs) were analyzed with an online gas chromatograph mass spectrometer, whereas the composition and size distribution of submicron particles was measured with a soot particle aerosol mass spectrometer.

This study showed that aVOC concentrations were significantly higher than bVOC concentrations at the street canyon. The largest aVOC concentrations were measured for toluene (campaign-average 1630 ng m-3) and p/m xylene (campaign-average 1070 ng m-3), while the dominating bVOCs was α-pinene (campaign-average 200 ng m-3). The special focus of this research was also on the oxidation of VOCs and the association between VOCs and OA in ambient air. Production rates of the oxidized compounds (OxPR) from the VOC reactions revealed that the main local sources of the oxidation products were O3 oxidation of bVOCs (66 % of total OxPR) and OH radical oxidation of aVOCs and bVOCs (25 % of total OxPR). Overall, aVOCs produced much smaller portion of the oxidation products (18 %) than bVOCs (82 %). For particle phase organics, the source apportionment analysis extracted six factors for OA. Three OA factors were related to primary OA sources, traffic (24 % of OA, two OA types) and coffee roastery (7 % of OA), whereas the largest fraction of OA (69 %) consisted of oxygenated OA (OOA). OOA was divided into less oxidized semi-volatile OA (SV-OOA; 40 % of OA) and two types of low-volatility OA (LV-OOA; 30 %). SV-OOA was likely to originate from biogenic sources since it correlated with an oxidation product of monoterpene, nopinone. LV-OOA consisted of highly oxygenated long-range or regionally transported OA that had no correlation with local oxidant concentrations as it had already spent several days in the atmosphere before reaching the measurement site.

By investigating specific air quality cases, it was noticed that the influence of main pollutant sources was different for VOCs and OA at the street canyon. Vehicle emissions impacted both VOC and OA concentrations, whereas the influence of biogenic emissions was more clearly detected in the VOC concentrations than in OA due to the specific VOCs attributed to biogenic emissions. In contrast, the emissions from the local coffee roastery had a distinctive mass spectrum for OA but they could not be seen in the VOC measurements due to the measurement limitations for the large VOC compounds. Long-range transport increased the OA concentrations and oxidation state considerably, while its effect was observed less clearly in the VOC measurements due to the oxidation of most VOC in the atmosphere during the transport. Overall, this study revealed that in order to properly characterize the impact of different emission sources to air quality, health and climate, it is of importance to describe both gaseous and particulate emissions and understand how they interact as well as their phase transfers in the atmosphere during the aging process.

Sanna Saarikoski et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-467', Anonymous Referee #1, 10 Oct 2022
  • RC2: 'Comment on acp-2022-467', Anonymous Referee #2, 24 Oct 2022

Sanna Saarikoski et al.

Sanna Saarikoski et al.

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Short summary
This study elucidates properties and sources of the volatile organic compounds (VOCs) and organic aerosol (OA) a street canyon. Anthropogenic VOCs were clearly higher than biogenic VOCs (bVOCs) but bVOCs produced larger portion of the oxidation products. OA consisted mostly of oxygenated OA representing secondary OA (SOA). SOA was partly associated with bVOCs but it was also related to long-range transport. Primary OA originated mostly from traffic and a small portion from local coffee roastery.
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