Characterization of NR-PM1 and source apportionment of organic aerosol in Krakow, Poland

Krakow is routinely affected by very high air pollution levels, especially during the winter months. Although a lot of effort has been done on characterization of ambient aerosols, there is a lack of online and long-term measurements of non-refractory aerosols. Our measurements at AGH University provide online long-term chemical composition of ambient submicron particulate matter (PM₁) between January 2018 and April 2019. Here we report the chemical characterization of non-refractory submicron aerosols and source apportionment of the organic fraction by positive matrix factorization (PMF). In contrast to other long-term source apportionment studies, we let a small PMF window roll over the dataset instead of performing PMF over the full dataset or on separate seasons. In this way, the seasonal variation of the source profiles can be captured. The uncertainties of the PMF solutions are addressed by the bootstrap resampling strategy and the random <em>a</em>-value approach for constrained factors. We observe clear seasonal patterns in concentration and composition of PM₁, with high concentrations during the winter months and lower concentrations during the summer months. Organics are the dominant species throughout the campaign. Five organic aerosol (OA) factors are resolved, of which three are of primary nature (hydrocarbon-like OA (HOA), biomass burning OA (BBOA) and coal combustion OA (CCOA)) and two are of secondary nature (more oxidized oxygenated OA (MO-OOA) and less oxidized oxygenated OA (LO-OOA)). While HOA contributes on average 8.6 % ± 2.3 % throughout the campaign, the solid fuel combustion related BBOA and CCOA show a clear seasonal trend with average contributions of 10.4 % ± 2.7 % and 14.1 %, ± 2.1 % respectively. Not only BBOA but also CCOA is associated with residential heating because of the pronounced yearly cycle where the highest contributions are observed during wintertime. Throughout the campaign, the OOA can be separated into MO-OOA and LO-OOA with average contribution of 38.4 % ± 8.4 % and 28.5 % ± 11.2 %, respectively.克拉科夫（Krakow）长期遭受高浓度空气污染困扰，尤以冬季为甚。尽管学界已针对环境气溶胶的表征开展大量研究，但目前仍缺乏非难熔气溶胶（non-refractory aerosols）的在线长期监测数据。我们在AGH大学（AGH University）开展的监测工作，获取了2018年1月至2019年4月期间环境亚微米颗粒物（PM₁）的在线长期化学成分组成数据集。 本研究报道了非难熔亚微米气溶胶的化学表征结果，并通过正矩阵因子分解法（positive matrix factorization, PMF）对其有机组分进行源解析。与其他长期源解析研究不同，我们采用滑动小窗口PMF分析策略处理数据集，而非对全数据集或分季节数据集单独开展PMF分析，以此实现源谱季节变化的有效捕捉。 PMF解析结果的不确定性通过bootstrap重采样策略，以及约束因子的随机α值方法进行量化评估。研究观测到PM₁的浓度与组分存在清晰的季节特征：冬季浓度较高，夏季浓度较低。有机组分是整个监测周期内的首要污染物。 本次研究共解析出5种有机气溶胶（organic aerosol, OA）因子，其中3种为一次源因子：类烃有机气溶胶（hydrocarbon-like OA, HOA）、生物质燃烧有机气溶胶（biomass burning OA, BBOA）与燃煤有机气溶胶（coal combustion OA, CCOA）；剩余2种为二次源因子：强氧化含氧有机气溶胶（more oxidized oxygenated OA, MO-OOA）与弱氧化含氧有机气溶胶（less oxidized oxygenated OA, LO-OOA）。 HOA在整个监测周期内的平均占比为8.6%±2.3%。与固体燃料燃烧相关的BBOA与CCOA则呈现显著的季节变化趋势，平均占比分别为10.4%±2.7%与14.1%±2.1%。由于全年循环特征显著——冬季贡献占比最高——不仅BBOA，CCOA也与民用采暖活动密切相关。 整个监测周期内，含氧有机气溶胶可被划分为MO-OOA与LO-OOA，二者的平均占比分别为38.4%±8.4%与28.5%±11.2%。