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

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 15 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 20 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 of VOCs the between VOCs OA ambient of the oxidized compounds (OxPR) the local of the oxidation products 3 oxidation of bVOCs (66% of total OxPR) and OH oxidation of aVOCs and bVOCs (25 % of total OxPR). of the oxidation products (18 %) than bVOCs (82 %). phase organics, apportionment six factors for OA. OA (24 % OA, roastery (7 % of OA), (69 (OOA). (SV-OOA; (LV-OOA; no local 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. likely to be localized and thus of variable impact at the sampling location. The aim of this study was to investigate the characteristics and sources of VOCs and particulate submicron (< 1 µm in diameter) OA at a street canyon in late summer. For the first time in Helsinki, a wide range of aVOCs and bVOCs was analyzed with an online gas chromatograph mass spectrometer (GC-MS). The 1-hour time-resolution for the VOC data enabled the study of short-term variability of the concentrations and allowed for comparisons with particle measurements conducted with a real-time aerosol mass spectrometer (AMS). The OA mass spectra 105 from the AMS was further analyzed by positive matrix factorization (PMF) for the sources and properties of OA. The specificity of the AMS source apportionment and VOC concentrations to various urban sources were examined by selecting four time periods that were examined in detail. Moreover, the oxidation of VOCs was investigated thoroughly by calculating the production rates of the VOC oxidation products, and their contribution to SOA formation was assessed. This study provides novel information on the sources of anthropogenic and 110 biogenic VOCs and OA in an urban environment and elucidate atmospheric oxidation processes and SOA formation in a street canyon. This information is currently highly needed by air quality authorities and modelers all over the world to improve urban air quality as well as the models for aerosol dynamics and atmospheric chemistry. data are 690 much more source-specific than the number concentrations and size distributions. In terms of the chemical composition of the ultrafine particles, this study was lacking a method for the smallest particles as the measurement range of the AMS started at ~60 nm. Often the identification of VOC and OA sources is challenging in urban areas due to high background concentrations and complex reactions in the atmosphere. In Helsinki, the pollutant background concentrations are 695 low, and even at the street canyon, the impact of traffic emissions is moderate. This enables detailed identification and characterization of various local sources such as the coffee roastery or limonene associated with human induced emissions. Overall, the results of this study indicate that the use of volatile organic markers complement the sources apportionment of OA. However, proper markers both for gas and particle phases still need to be identified in order to achieve a comprehensive source analysis for gas and particle phase organics. Another 700 approach could be combining VOC and OA data in the same statistical data analysis method, but the interpretation of the results can be challenging due to e.g. different rates for the atmospheric processes. Data availability. The data shown in the paper is available on request from corresponding author.