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.

中文翻译：

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表征街道峡谷环境中 VOC 和亚微米有机气溶胶的特性

摘要。城市空气由来自人为和生物来源的气体和颗粒物质的复杂混合物组成，这些物质在大气中进一步处理。本研究调查了夏末芬兰赫尔辛基街头峡谷中挥发性有机化合物 (VOC) 和亚微米有机气溶胶 (OA) 的特征和来源。主要人为 VOCs (aVOCs) 和生物源 VOCs (bVOCs) 采用在线气相色谱质谱仪进行分析，而亚微米颗粒的组成和尺寸分布采用烟尘颗粒气溶胶质谱仪进行测量。这项研究表明，街道峡谷的 aVOC 浓度明显高于 bVOC 浓度。测量甲苯的最大 aVOC 浓度（活动平均 1630 ng m ^-3) 和 p/m 二甲苯（活动平均 1070 ng m ^-3），而主要的 bVOC 是 α-蒎烯（活动平均 200 ng m ^-3）。这项研究的特别重点还在于 VOC 的氧化以及环境空气中 VOC 与 OA 之间的关联。VOC 反应中氧化化合物 (OxPR) 的产率表明，氧化产物的主要局部来源是 O ₃bVOC 的氧化（占 OxPR 总量的 66%）和 aVOC 和 bVOC 的 OH 自由基氧化（占 OxPR 总量的 25%）。总体而言，aVOCs 产生的氧化产物比例 (18%) 比 bVOCs (82%) 小得多。对于颗粒相有机物，源解析分析提取了 OA 的六个因素。三个 OA 因素与主要 OA 来源、交通（OA 的 24%，两种 OA 类型）和咖啡烘焙（OA 的 7%）有关，而 OA 的最大部分（69%）由含氧 OA（OOA）组成。OOA分为氧化程度较低的半挥发性OA（SV-OOA；OA的40%）和低挥发性OA（LV-OOA；30%）两类。SV-OOA 可能来源于生物来源，因为它与单萜烯的氧化产物诺皮酮有关。LV-OOA 由高度氧化的远程或区域运输的 OA 组成，与当地氧化剂浓度无关，因为它在到达测量地点之前已经在大气中呆了几天。通过对具体空气质量案例的调查，发现街道峡谷主要污染源对VOCs和OA的影响是不同的。车辆排放对 VOC 和 OA 浓度都有影响，而由于特定 VOC 归因于生物排放，因此在 VOC 浓度中比在 OA 中更清楚地检测到生物排放的影响。相比之下，当地咖啡烘焙厂的排放物具有独特的 OA 质谱，但由于大 VOC 化合物的测量限制，它们无法在 VOC 测量中看到。远距离传输显着增加了 OA 浓度和氧化态，而在 VOC 测量中观察到的效果不太明显，因为在传输过程中大气中的大多数 VOC 被氧化。总体而言，这项研究表明，为了正确描述不同排放源对空气质量、健康和气候的影响，描述气体和颗粒物排放并了解它们如何相互作用以及它们在大气中的相转移非常重要在老化过程中。