Effect of relative humidity on the composition of secondary organic aerosol from the oxidation of toluene
Effect of relative humidity on the composition of secondary organic aerosol from the oxidation of toluene
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DOI：
10.5194/acp-18-1643-2018
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发表时间：
2018-02-06
影响因子：
6.3
通讯作者：
Nizkorodov, Sergey A.
中科院分区：
文献类型：
--
作者：
Hinks, Mallory L.;Montoya-Aguilera, Julia;Nizkorodov, Sergey A.
研究了在无种子颗粒的情况下，相对湿度（RH）对低nox甲苯氧化形成的二次有机气溶胶（SOA）化学成分的影响。在< 2% RH和75% RH的气溶胶雾霾室中制备SOA样品，在聚四氟乙烯过滤器上收集，并使用纳米喷雾解吸电喷雾电离高分辨率质谱法（nano-DESI-HRMS）进行分析。测量结果显示，与在干燥条件下生成的SOA相比，在75% RH条件下生成的SOA中存在的低聚物的比例显著减少。在另一组实验中，用扫描迁移率粒度仪（SMPS）测量了RHs < 2 ~ 90%范围内的颗粒质量浓度。结果表明，低nox甲苯SOA中，当相对湿度从< 2增加到75-90%时，颗粒质量负荷下降了近一个数量级。利用“分子走廊”方法从分子式分布中估计出SOA化合物的挥发性分布，证实了低nox甲苯SOA在高rh条件下的平均挥发性更强。相比之下，对于高nox甲苯SOA， RH对SOA质量负载的影响要小得多。在干燥条件下观察到的低聚物分数和颗粒质量负载的增加归因于冷凝反应的增强，在低nox甲苯SOA中，较小的化合物产生水和低聚物。预计在潮湿条件下低聚化合物的减少部分抵消了先前观察到的由溶解的无机种子颗粒中的气溶胶液态水化学驱动的甲苯SOA产率的增强。
The effect of relative humidity (RH) on the chemical composition of secondary organic aerosol (SOA) formed from low-NOx toluene oxidation in the absence of seed particles was investigated. SOA samples were prepared in an aerosol smog chamber at < 2% RH and 75% RH, collected on Teflon filters, and analyzed with nanospray desorption electrospray ionization high-resolution mass spectrometry (nano-DESI-HRMS). Measurements revealed a significant reduction in the fraction of oligomers present in the SOA generated at 75% RH compared to SOA generated under dry conditions. In a separate set of experiments, the particle mass concentrations were measured with a scanning mobility particle sizer (SMPS) at RHs ranging from < 2 to 90 %. It was found that the particle mass loading decreased by nearly an order of magnitude when RH increased from < 2 to 75-90% for low-NOx toluene SOA. The volatility distributions of the SOA compounds, estimated from the distribution of molecular formulas using the "molecular corridor" approach, confirmed that low-NOx toluene SOA became more volatile on average under high-RH conditions. In contrast, the effect of RH on SOA mass loading was found to be much smaller for high-NOx toluene SOA. The observed increase in the oligomer fraction and particle mass loading under dry conditions were attributed to the enhancement of condensation reactions, which produce water and oligomers from smaller compounds in low-NOx toluene SOA. The reduction in the fraction of oligomeric compounds under humid conditions is predicted to partly counteract the previously observed enhancement in the toluene SOA yield driven by the aerosol liquid water chemistry in deliquesced inorganic seed particles.