Abstract In this study, we investigated the impact of biomass burning on the oxidative potential of PM2.5 in the metropolitan area of Milan, Italy. PM2.5 samples were collected on quartz filters during cold (December 2018–February 2019) and warm (May 2019–July 2019) seasons at the Municipality of Bareggio, a small town located approximately 14 km northwest of the Milan city center. The PM2.5 constituents were chemically analyzed, and its corresponding oxidative potential was measured by means of the dithiothreitol (DTT) assay. Total PM2.5 mass concentration was significantly higher in winter (71.82 ± 4.17 μg/m3) compared to summer (16.67 ± 0.27 μg/m3), mainly a result of enhanced biomass burning emissions combined with higher atmospheric stability and lower mixing during the cold season. The enhanced biomass burning activities during the winter period also resulted in very high polycyclic aromatic hydrocarbons (PAHs) concentrations (72.81 ± 16.59 ng/m3) which were more than 150-fold higher than the warm period values (0.40 ± 0.07 ng/m3). PAH concentrations were highly correlated with chemical markers of biomass burning (i.e., levoglucosan (R2 = 0.79), and K+/K (R2 = 0.87)) in the winter period. Spearman correlation analysis between DTT and PM2.5 chemical species showed a dominant role of secondary organic aerosols (SOA) and vehicular emissions in summer-time PM2.5 oxidative potential (i.e., the capacity of PM2.5 species to oxidize target molecules), while in the wintertime, the DTT values were highly correlated with chemical markers of biomass burning, vehicular activities, and re-suspended road dust. Multiple linear regression (MLR) analysis identified biomass burning (41%) as the dominant contributor to DTT, followed by SOA (20%), re-suspended road dust (18%), and vehicular emissions (16%). Our results underscore the importance of biomass burning to the overall oxidative potential of PM2.5 in the metropolitan area of Milan, urging the need to promulgate effective mitigation policies targeting these emissions.

中文翻译：

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生物质燃烧对米兰大都市区PM2.5氧化潜能的影响

摘要 在这项研究中，我们调查了生物质燃烧对意大利米兰大都市区 PM2.5 氧化潜力的影响。PM2.5 样本是在寒冷季节（2018 年 12 月至 2019 年 2 月）和温暖季节（2019 年 5 月至 2019 年 7 月）在位于米兰市中心西北约 14 公里的小镇巴雷焦市的石英过滤器上收集的。对 PM2.5 成分进行化学分析，并通过二硫苏糖醇 (DTT) 测定法测量其相应的氧化电位。与夏季 (16.67 ± 0.27 μg/m3) 相比，冬季 PM2.5 的总质量浓度显着更高 (71.82 ± 4.17 μg/m3)，这主要是由于生物质燃烧排放量增加，加上更高的大气稳定性和寒冷期间较低的混合季节。冬季生物质燃烧活动的增强也导致了非常高的多环芳烃 (PAH) 浓度 (72.81 ± 16.59 ng/m3)，比暖期值 (0.40 ± 0.07 ng/m3) 高出 150 多倍. PAH 浓度与冬季生物质燃烧的化学标志物（即左旋葡聚糖 (R2 = 0.79) 和 K+/K (R2 = 0.87)）高度相关。DTT 与 PM2.5 化学物种之间的 Spearman 相关分析表明，二次有机气溶胶 (SOA) 和车辆排放在夏季 PM2.5 氧化潜力（即 PM2.5 物种氧化目标分子的能力）中起主导作用，而在冬季，DTT 值与生物质燃烧、车辆活动和重新悬浮的道路灰尘的化学标​​志高度相关。多元线性回归 (MLR) 分析确定生物质燃烧 (41%) 是 DTT 的主要贡献者，其次是 SOA (20%)、重新悬浮的道路灰尘 (18%) 和车辆排放 (16%)。我们的结果强调了生物质燃烧对米兰大都市区 PM2.5 整体氧化潜力的重要性，敦促有必要颁布针对这些排放的有效缓解政策。