Average versus high surface ozone levels over the continental U.S.A.: Model bias, background influences, and interannual variability: Data and code

This file contains data and code for the figures in the paper "Average versus high surface ozone levels over the continental U.S.A.: Model bias, background influences, and interannual variability." Article abstract: U.S. background ozone (O3) includes O3 produced from anthropogenic O3 precursors emitted outside of the U.S.A., from global methane, and from any natural sources. Using a suite of sensitivity simulations in the GEOS-Chem global chemistry-transport model, we estimate the influence from individual background versus U.S. anthropogenic sources on total surface O3 over ten continental U.S. regions from 2004–2012. Evaluation with observations reveals model biases of +0–19ppb in seasonal mean maximum daily 8-hour average (MDA8) O3, highest in summer over the eastern U.S.A. Simulated high-O3 events cluster too late in the season. We link these model biases to regional O3 production (e.g., U.S. anthropogenic, biogenic volatile organic compounds (BVOC), and soil NOx, emissions), or coincident missing sinks. On the ten highest observed O3 days during summer (O3_top10obs_JJA), U.S. anthropogenic emissions enhance O3 by 5–11ppb and by less than 2ppb in the eastern versus western U.S.A. The O3 enhancement from BVOC emissions during summer is 1–7ppb higher on O3_top10obs_JJA days than on average days, while intercontinental pollution is up to 2ppb higher on average vs. on O3_top10obs_JJA days. In the model, regional sources of O3 precursor emissions drive interannual variability in the highest observed O3 levels. During the summers of 2004–2012, monthly regional mean U.S. background O3 MDA8 levels vary by 10–20ppb. Simulated summertime total surface O3 levels on O3_top10obs_JJA days decline by 3ppb (averaged over all regions) from 2004–2006 to 2010–2012 in both the observations and the model, reflecting rising U.S. background (+2ppb) and declining U.S. anthropogenic O3 emissions (−6ppb). The model attributes interannual variability in U.S. background O3 on O3_top10obs days to natural sources, not international pollution transport. We find that a three-year averaging period is not long enough to eliminate interannual variability in background O3.

本文件包含论文《美国大陆地表臭氧平均水平与高值水平的对比：模型偏差、背景影响及年际变率》中所有图表的数据与代码。论文摘要：美国背景臭氧（O3）包括由美国境外排放的人为O3前体物、全球甲烷以及各类自然源生成的O3。通过GEOS-Chem全球化学传输模型中的一系列敏感性模拟，我们估算了2004–2012年间，各背景源与美国人为源对美国大陆10个区域地表总O3的影响。观测评估结果显示，模型对季节性平均日最大8小时平均（MDA8）O3的模拟偏差为+0–19ppb，其中美国东部夏季的偏差最大。模拟的高O3事件在季节内的发生时间偏晚。我们将这些模型偏差与区域O3生成（如美国人为排放、生物源挥发性有机化合物（BVOC）及土壤NOx排放）或模型中未考虑的汇相关联。在夏季观测到的O3浓度最高的10天（O3_top10obs_JJA），美国人为排放在东部使O3浓度升高5–11ppb，而在西部的升高幅度小于2ppb。夏季BVOC排放对O3的贡献在O3_top10obs_JJA日比平均日高1–7ppb，而洲际污染的贡献在平均日比O3_top10obs_JJA日高多达2ppb。模型结果表明，O3前体物的区域排放源是观测到的最高O3水平年际变率的驱动因素。2004–2012年夏季期间，美国区域月平均背景O3 MDA8水平的变幅为10–20ppb。2004–2006年至2010–2012年间，O3_top10obs_JJA日的夏季地表总O3水平（所有区域平均值）下降了3ppb，这反映了美国背景O3的上升（+2ppb）与美国人为O3前体物排放的下降（−6ppb）。模型将O3_top10obs日美国背景O3的年际变率归因于自然源，而非国际污染传输。我们发现，三年的平均周期不足以消除背景O3的年际变率。