PM2.5 chemistry, organosulfates, and secondary organic aerosol during the 2017 Lake Michigan Ozone Study
PM2.5 chemistry, organosulfates, and secondary organic aerosol during the 2017 Lake Michigan Ozone Study
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DOI：
10.1016/j.atmosenv.2020.117939
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发表时间：
2021-01-01
影响因子：
5
通讯作者：
Stone, Elizabeth A.
中科院分区：
文献类型：
--
作者：
Hughes, Dagen D.;Christiansen, Megan B.;Stone, Elizabeth A.
2017年5月21日至6月23日的密歇根湖臭氧研究(LMOS 2017)旨在更好地了解密歇根湖沿岸臭氧和细颗粒物(PM2.5)的人为和生物来源。在这里，我们重点研究伊利诺伊州锡安市一个地面超级站点白天和夜间PM2.5的化学成分，特别是有机碳、无机离子和有机硫酸盐。PM2.5质量浓度范围为1.5-12.9微克米(-3)，平均(正负标准误差)为5.2+/-0.4微克米(-3)。对PM2.5质量贡献最大的是有机质(OM；计算为1.7 x有机碳[OC]；平均贡献59+/-2%)，其次是硫酸盐(17+/-1%)、铵(6.3+/-0.3%)、硝酸盐(3.5+/-0.4%)和元素碳(EC；3.4+/-0.2%)。在三个臭氧高发期，PM2.5都有不同的区域特征。A期(6月2日至3日)受到湖风和席卷主要城市地区的东南气团的影响。时段A的PM2.5日质量浓度最高(11.4+/-1.5µg m(-3))，EC的OC/EC比值较低，为7.0，说明低OC/EC比来源的影响，包括化石燃料和生物质的人为燃烧。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)的混合比升高。有机硫酸盐的峰值浓度，包括甲基四氢呋喃硫酸盐(m/z 215；C5H11SO7)也在整个B期间观察到，C期间(6月13日至17日)随偏北风变化而变化。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，有机硫酸盐平均占有机质的4%，在B阶段占有机质的15%。有机硫酸盐主要来自异戊二烯，较少的贡献来自单萜(0.3%)和人为来源(0.5%)。通过对大湖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，并确定了特别是异戊二烯衍生的有机硫酸盐对PM2.5的显著贡献。对于其他LMOS观测，PM2.5的化学特征和反向轨迹表明，臭氧事件与气团内的局部湖风气象共存，在化学史和来源区域中，气团事件随事件的不同而不同。
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 mu g m(-3) with an average (+/- standard error) of 5.2 +/- 0.4 mu g m(-3). The most significant contributor to PM2.5 mass was organic matter (OM; calculated as 1.7 x 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 mu g 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 meth-yltetrol 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.