Department of Soil and Water Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, Hebrew University of Jerusalem, Rehovot, Israel.
Department of Soil and Water Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, Hebrew University of Jerusalem, Rehovot, Israel.
Environ Pollut. 2019 Sep;252(Pt B):1863-1871. doi: 10.1016/j.envpol.2019.05.142. Epub 2019 Jun 8.
Alternative transportation fuels (ATFs) can reduce air pollution. However, the influence of conventional fuels-diesel and gasoline, and particularly ATFs on photochemical air pollution is not well-characterized, limiting assessments of ATFs and air quality. This is mainly due to frequent use of lumped chemical mechanisms by related atmospheric modeling. Here we hypothesized that applying a chemical mechanism that is specifically developed according to both emission fractions and photochemical ozone creation potential of volatile organic compounds (VOCs) is key to gaining reliable insights into the impact of transportation fuels on photochemistry. We used a heterogeneous chemical mechanism with 927 reactions and relatively detailed emission inventories to specifically meet the requirements for reliable simulation of the effect of exhaust emissions from vehicles fueled by selected model fuels-diesel, gasoline, and mixtures of 15% gasoline with 85% ethanol (E85) or 85% methanol (M85)-on photochemistry. These dispersion-box model simulations revealed a strong influence of atmospheric background balance between VOCs and nitrogen oxides (NO = [NO] + [NO]) on the impact of exhaust emissions on photochemistry, with higher tendency toward ozone (O) formation or destruction for more VOC-limited or NO-limited conditions, respectively. Accordingly, higher [NO]/[VOC] exhaust emission, such as from diesel and M85, resulted in lower O, not only locally but also downwind of the emission. This offers a new perspective and measure for transportation fuel assessment. Rapid conversion of O to hydroxyl and hydroperoxyl radicals downwind of the exhaust emission indicates the importance of simulating the impact of road transportation on photochemistry at high spatial and temporal resolution. Peroxyacetyl nitrate formation was more sensitive to VOC emission under VOC-limited conditions than to NO emission under NO-limited conditions. Secondary formaldehyde dominated over primary emitted formaldehyde several minutes after emission. These findings should be verified using a 3D modeling study under varying meteorological conditions.
替代交通燃料（ATFs）可以减少空气污染。然而，常规燃料——柴油和汽油，特别是 ATFs 对光化学空气污染的影响尚未得到很好的描述，这限制了对 ATFs 和空气质量的评估。这主要是由于相关大气模式模拟中频繁使用综合化学机制。在这里，我们假设应用一种根据挥发性有机化合物（VOC）的排放分数和光化学臭氧生成潜能专门开发的化学机制是获得有关运输燃料对光化学影响的可靠见解的关键。我们使用了一种具有 927 个反应的多相化学机制和相对详细的排放清单，专门满足可靠模拟选定模型燃料（柴油、汽油和 15%汽油与 85%乙醇（E85）或 85%甲醇（M85）混合物）车辆尾气排放对光化学影响的要求。这些分散箱模型模拟表明，大气背景中 VOC 和氮氧化物（NO = [NO]+[NO]）之间的平衡对尾气排放对光化学的影响有很大影响，对于更受 VOC 限制或 NO 限制的条件，分别有更高的臭氧（O）形成或破坏的趋势。因此，较高的[NO]/[VOC]尾气排放，如柴油和 M85，导致较低的 O，不仅在局部，而且在排放下风处。这为运输燃料评估提供了新的视角和衡量标准。O 在尾气排放下风处迅速转化为羟基和过氧氢自由基，表明需要以高时空分辨率模拟道路交通对光化学的影响。在 VOC 限制条件下，过氧乙酰硝酸盐的形成对 VOC 排放比在 NO 限制条件下对 NO 排放更敏感。在排放几分钟后，二次甲醛超过了一次排放的甲醛。这些发现应在不同气象条件下的 3D 建模研究中进行验证。
