ABSTRACT This paper examines the spatiotemporal impact of changing local precursor emissions on a subset of air quality monitors in the coastal Lower Fraser Valley, British Columbia, Canada, over a 25-year period (1990–2014) marked by substantial emissions reductions. The analysis examines summertime (JJA) trends in ambient reactivity of volatile organic compounds (VOCs), , ozone, and odd oxygen (; defined as ) concentrations. To account for the potentially confounding influence of rising background ozone levels on the analysis, summer days are classified by whether appreciable local ozone production is likely or not, with a separate analysis undertaken for each set of conditions. The influence of short- and long-term meteorological variability, hebdomadal (weekly) emissions variability, and within-network spatial variability on long-term trends is accounted for by using Generalized Additive Models (GAM). The analysis suggests that long-term trends in local ambient VOC reactivity and concentrations have not occurred in a uniform fashion nor have they changed in a synchronized way. Declines in VOC reactivity appear to have occurred sooner and at a more uniform rate, but concentrations appear to have remained constant for the first 10 years before rapidly declining. Similarly, we find ozone reductions have not occurred uniformly in time nor has the network response been spatially uniform, with the smallest reductions occurring just downwind of the region's downtown core and the largest reductions about 40 km further downwind. Much of the non-uniformity in response can be attributed to changing odd-oxygen partitioning rather than changing ozone production. During our analysis period, ozone concentrations during days not conducive to ozone photochemistry appear to have increased at a rate consistent with previous background trend analyses over western North America. We use the difference between ozone concentrations on fair-weather summer days and days with little photochemistry to build a response surface for “net-produced” ozone as a function of meteorologically controlled ambient VOC reactivity and concentrations. We find that much of the predicted behaviour in local ambient ozone can be understood in light of VOC-limited conditions and differing rates of local VOC and emissions reductions. It appears that these precursor reductions have largely resulted from evolving light-duty emission control technologies and local fleet turnover.

中文翻译：

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夏季对流层臭氧对不列颠哥伦比亚省下弗雷泽河谷当地前体排放变化的时空响应

摘要 本文研究了在 25 年（1990-2014 年）期间，以大幅减排为标志的加拿大不列颠哥伦比亚省下弗雷泽河谷沿海地区，局部前体排放变化对空气质量监测子集的时空影响。该分析检查了夏季 (JJA) 挥发性有机化合物 (VOC)、臭氧和奇数氧 (; 定义为 ) 浓度的环境反应性趋势。考虑到背景臭氧水平上升对分析的潜在混杂影响，根据是否可能产生可观的局部臭氧对夏季进行分类，并对每组条件进行单独分析。短期和长期气象变异性的影响，hebdomadal（每周）排放变异性，使用广义加性模型 (GAM) 解释长期趋势的网络内空间变异性。分析表明，局部环境 VOC 反应性和浓度的长期趋势并没有以统一的方式发生，也没有以同步的方式发生变化。VOC 反应性的下降似乎发生得更早且速度更均匀，但浓度似乎在前 10 年保持不变，然后迅速下降。同样，我们发现臭氧减少在时间上并不一致，网络响应在空间上也不一致，最小的减少发生在该地区市中心的下风向，最大的减少发生在下风约 40 公里处。响应的大部分不均匀性可归因于改变奇数氧分配而不是改变臭氧产生。在我们的分析期间，在不利于臭氧光化学的日子里，臭氧浓度似乎以与之前北美西部背景趋势分析一致的速度增加。我们使用晴天夏季和几乎没有光化学的日子的臭氧浓度差异来构建“净产生”臭氧的响应面，作为气象控制的环境 VOC 反应性和浓度的函数。我们发现，根据 VOC 限制条件以及当地 VOC 和排放减少的不同速率，可以理解当地环境臭氧中的大部分预测行为。