Abstract The Lake Michigan Ozone Study from 21 May to 23 June 2017 (LMOS 2017) aimed to better understand the anthropogenic and biogenic sources that contribute to ozone and fine particles (PM2.5) along the coast of Lake Michigan. Here, we focus on the chemical composition of daytime and nighttime PM2.5—especially organic carbon, inorganic ions and organosulfates—at a ground-based supersite in Zion, Illinois. PM2.5 mass concentrations ranged from 1.5 to 12.9 μg m−3 with an average (±standard error) of 5.2 ± 0.4 μg m−3. The most significant contributor to PM2.5 mass was organic matter (OM; calculated as 1.7 × organic carbon [OC]; contributing an average of 59 ± 2%), followed by sulfate (17 ± 1%), ammonium (6.3 ± 0.3%), nitrate (3.5 ± 0.4%), and elemental carbon (EC; 3.4 ± 0.2%). During each of the three periods of high ozone, PM2.5 had different regional characteristics. Period A (2–3 June) was impacted by lake breeze and south-easterly air masses that travelled over major urban areas. Period A had the highest daily PM2.5 mass concentrations (11.4 ± 1.5 μg m−3) and EC with a relatively low OC:EC ratio of 7.0, indicating the influence of sources with low OC:EC ratios, which includes the anthropogenic combustion of fossil fuels and biomass. Period B (10–13 June) was impacted by air masses traveling from the southern US. It had a relatively high OC:EC ratio of 18, the highest PM2.5 sulfate concentrations and aerosol acidity, and elevated mixing ratios of isoprene along with its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR). Peak concentrations of organosulfates, including methyltetrol sulfate (m/z 215; C5H11SO7−), were also observed throughout period B. Period C (13–17 June) followed a change to northerly winds. PM2.5 concentrations decreased along with decreases in sulfate, acidity, and most organosulfates. Throughout the study, organosulfates accounted for an average of 4% of OM and up to 15% of OM in Period B. Organosulfates were largely isoprene-derived, with lessor contributions from monoterpenes (0.3%) and anthropogenic sources (0.5%). Through these measurements of organosulfates in the Great Lakes region, we demonstrate the importance of anthropogenic sulfate emissions and aerosol acidity on SOA formation, and establish that isoprene-derived organosulfates, in particular, contribute significantly to PM2.5. With other LMOS observations, the chemical signatures of PM2.5, and back trajectories show that ozone episodes cooccur with localized lake-breeze meteorology within air masses that vary from episode to episode in chemical history and source region.

中文翻译：

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2017 年密歇根湖臭氧研究期间的 PM2.5 化学、有机硫酸盐和二次有机气溶胶

摘要 2017 年 5 月 21 日至 6 月 23 日的密歇根湖臭氧研究 (LMOS 2017) 旨在更好地了解导致密歇根湖沿岸臭氧和细颗粒 (PM2.5) 的人为和生物源。在这里，我们关注伊利诺伊州锡安的一个地面超级站点中白天和夜间 PM2.5 的化学成分，尤其是有机碳、无机离子和有机硫酸盐。PM2.5 质量浓度范围为 1.5 至 12.9 μg m-3，平均值（±标准误差）为 5.2 ± 0.4 μg m-3。PM2.5 质量的最重要贡献者是有机物（OM；计算为 1.7 × 有机碳 [OC]；贡献平均为 59 ± 2%），其次是硫酸盐 (17 ± 1%)、铵盐 (6.3 ± 0.3 %)、硝酸盐 (3.5 ± 0.4%) 和元素碳 (EC; 3.4 ± 0.2%)。在三个高臭氧时期的每个时期，PM2. 5具有不同的地域特征。A 期（6 月 2 日至 3 日）受到湖风和在主要城市地区传播的东南气团的影响。A 时期的 PM2.5 日质量浓度最高（11.4 ± 1.5 μg m-3），EC 的 OC:EC 比率相对较低，为 7.0，表明 OC:EC 比率较低的来源的影响，包括人为燃烧化石燃料和生物质。B 期（6 月 10 日至 13 日）受到来自美国南部的气团的影响。它具有相对较高的 OC:EC 比率 18、最高的 PM2.5 硫酸盐浓度和气溶胶酸度，以及异戊二烯及其氧化产物甲基乙烯基酮 (MVK) 和甲基丙烯醛 (MACR) 的混合比率升高。在整个 B 阶段也观察到有机硫酸盐的峰值浓度，包括甲基四醇硫酸盐 (m/z 215; C5H11SO7−)。C 期（6 月 13 日至 17 日）随后转为偏北风。PM2.5 浓度随着硫酸盐、酸度和大多数有机硫酸盐的减少而下降。在整个研究过程中，有机硫酸盐平均占 OM 的 4%，在 B 期占 OM 的高达 15%。有机硫酸盐主要来自异戊二烯，单萜 (0.3%) 和人为来源 (0.5%) 的贡献较少。通过对五大湖地区有机硫酸盐的这些测量，我们证明了人为硫酸盐排放和气溶胶酸度对 SOA 形成的重要性，并确定异戊二烯衍生的有机硫酸盐对 PM2.5 的贡献尤其显着。通过其他 LMOS 观测，PM2.5 的化学特征、