Strong wintertime ozone events in the Upper Green River basin, Wyoming
Strong wintertime ozone events in the Upper Green River basin, Wyoming
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DOI：
10.5194/acp-14-4909-2014
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发表时间：
2013-07
影响因子：
6.3
通讯作者：
B. Rappenglück;Luis Ackermann;Sergio Alvarez;J. Golovko;Martin Buhr;Robert A. Field;J. Soltis
中科院分区：
文献类型：
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作者：
B. Rappenglück;Luis Ackermann;Sergio Alvarez;J. Golovko;Martin Buhr;Robert A. Field;J. Soltis
抽象的。近年来，臭氧（O3）值升高已多次观察到在上游绿色河流域（UGRB），怀俄明州，在冬季。本文分析了2011年冬末的高臭氧日（1小时平均值高达166 ppbv -十亿分之一体积）。进行了环境监测的密集作业期，其中包括全面的表面和边界层测量。在IOP日，最大O3值仅限于非常浅的表面层。低风速和低混合层高度（中午时距地面约50米）是UGRB内污染物积累的关键。气团含有大量由派恩代尔背斜化石燃料勘探活动排放的活性氮（NOx）和非甲烷碳氢化合物（NMHC）。在IOP日，特别是在早晨，活性氮（高达69%）、芳烃和烷烃（约10-15%;主要是乙烷和丙烷）是羟基（OH）反应性的主要贡献者。在西南气流条件下，在这些时间段内，博尔德监测点的测量显示最低的NMHC / NOx比（~ 50），反映了相对较低的反应性NMHC混合物，以及从NOx限制状态向NMHC限制状态的变化，如光化学指标所示，O3 /NOy、O3 /NOz和O3 /HNO 3以及EOR（反应程度）。IOP日的OH产生主要是由于亚硝酸（HONO）。在24小时的基础上，并确定为测量高度为1.80米以上的表面上的HONO光解IOP天可以贡献约83%的OH生产平均，其次是烯烃臭氧分解（约9%）。臭氧的光解和甲醛的光解对羟基的形成各贡献约4%。高HONO水平（IOP天的最大小时中位数：1096 pptv -万亿分之一体积）是由浅边界层条件和增强的光解率，由于雪表面的高反射率的组合。HONO最有可能是通过以下方式形成的：（i）在大气氧化NOx时产生的大量硝酸（HNO 3），沉积在雪表面并经历光增强的非均相转化为HONO（估计HONO产生量：10.2 ± 40%ppbv h−1）和（ii）与燃烧相关的HONO排放（估计HONO产生量：~ 0.1 ± 30%ppbv h−1）。HONO的产生仅限于边界层的最低10 m处。HONO是OH最重要的前体，由于雪盖的高吸收而强烈增强（HONO光解率为10.7 ± 30%ppbv h−1）。OH自由基将氧化NMHC，主要是芳烃（甲苯，二甲苯）和烷烃（乙烷，丙烷），最终导致臭氧增加。
Abstract. During recent years, elevated ozone (O3) values have been observed repeatedly in the Upper Green River basin (UGRB), Wyoming, during wintertime. This paper presents an analysis of high ozone days in late winter 2011 (1 h average up to 166 ppbv – parts per billion by volume). Intensive operational periods (IOPs) of ambient monitoring were performed, which included comprehensive surface and boundary layer measurements. On IOP days, maximum O3 values are restricted to a very shallow surface layer. Low wind speeds in combination with low mixing layer heights (~ 50 m above ground level around noontime) are essential for accumulation of pollutants within the UGRB. Air masses contain substantial amounts of reactive nitrogen (NOx) and non-methane hydrocarbons (NMHC) emitted from fossil fuel exploration activities in the Pinedale Anticline. On IOP days particularly in the morning hours, reactive nitrogen (up to 69%), aromatics and alkanes (~ 10–15%; mostly ethane and propane) are major contributors to the hydroxyl (OH) reactivity. Measurements at the Boulder monitoring site during these time periods under SW wind flow conditions show the lowest NMHC / NOx ratios (~ 50), reflecting a relatively low reactive NMHC mixture, and a change from a NOx-limited regime towards a NMHC-limited regime as indicated by photochemical indicators, e.g., O3 /NOy, O3 /NOz, and O3 / HNO3 and the EOR (extent of reaction). OH production on IOP days is mainly due to nitrous acid (HONO). On a 24 h basis and as determined for a measurement height of 1.80 m above the surface HONO photolysis on IOP days can contribute ~ 83% to OH production on average, followed by alkene ozonolysis (~ 9%). Photolysis by ozone and HCHO photolysis contribute about 4% each to hydroxyl formation. High HONO levels (maximum hourly median on IOP days: 1096 pptv – parts per trillion by volume) are favored by a combination of shallow boundary layer conditions and enhanced photolysis rates due to the high albedo of the snow surface. HONO is most likely formed through (i) abundant nitric acid (HNO3) produced in atmospheric oxidation of NOx, deposited onto the snow surface and undergoing photo-enhanced heterogeneous conversion to HONO (estimated HONO production: 10.2 ± 40% ppbv h−1) and (ii) combustion-related emission of HONO (estimated HONO production: ~ 0.1 ± 30% ppbv h−1). HONO production is confined to the lowermost 10 m of the boundary layer. HONO, serves as the most important precursor for OH, strongly enhanced due to the high albedo of the snow cover (HONO photolysis rate 10.7 ± 30% ppbv h−1). OH radicals will oxidize NMHCs, mostly aromatics (toluene, xylenes) and alkanes (ethane, propane), eventually leading to an increase in ozone.