Department of Mechanical Engineering, Colorado State University , Fort Collins, Colorado 80525, United States.
Department of Chemistry, Colorado State University , Fort Collins, Colorado 80523, United States.
Environ Sci Technol. 2017 Feb 7;51(3):1377-1386. doi: 10.1021/acs.est.6b04602. Epub 2017 Jan 26.
Diesel engines are important sources of fine particle pollution in urban environments, but their contribution to the atmospheric formation of secondary organic aerosol (SOA) is not well constrained. We investigated direct emissions of primary organic aerosol (POA) and photochemical production of SOA from a diesel engine using an oxidation flow reactor (OFR). In less than a day of simulated atmospheric aging, SOA production exceeded POA emissions by an order of magnitude or more. Efficient combustion at higher engine loads coupled to the removal of SOA precursors and particle emissions by aftertreatment systems reduced POA emission factors by an order of magnitude and SOA production factors by factors of 2-10. The only exception was that the retrofitted aftertreatment did not reduce SOA production at idle loads where exhaust temperatures were low enough to limit removal of SOA precursors in the oxidation catalyst. Use of biodiesel resulted in nearly identical POA and SOA compared to diesel. The effective SOA yield of diesel exhaust was similar to that of unburned diesel fuel. While OFRs can help study the multiday evolution, at low particle concentrations OFRs may not allow for complete gas/particle partitioning and bias the potential of precursors to form SOA.
柴油机是城市环境中细颗粒物污染的重要来源，但它们对大气二次有机气溶胶（SOA）形成的贡献尚未得到很好的约束。我们使用氧化流动反应器（OFR）研究了柴油机的一次有机气溶胶（POA）直接排放和光化学 SOA 生成。在不到一天的模拟大气老化过程中，SOA 的生成量超过了 POA 排放量一个数量级以上。在较高的发动机负荷下进行高效燃烧，再加上后处理系统去除 SOA 前体和颗粒排放，使 POA 排放因子降低了一个数量级，SOA 生成因子降低了 2-10 倍。唯一的例外是，经过改装的后处理系统并没有降低怠速时的 SOA 生成，因为此时排气温度足够低，限制了氧化催化剂中 SOA 前体的去除。与柴油相比，生物柴油的使用导致 POA 和 SOA 几乎相同。柴油废气的有效 SOA 产率与未燃烧的柴油燃料相似。虽然 OFR 可以帮助研究多日的演化，但在低颗粒浓度下，OFR 可能无法实现完全的气/粒分配，并对前体形成 SOA 的潜力产生偏差。
