Local scale air quality impacts in the Los Angeles Basin from increased port activity during 2021 supply chain disruptions

Increased throughput and container ship backlogs at the Ports of Los Angeles and Long Beach due to supply chain disruptions related to the Covid-19 pandemic caused a significant increase in the number of ships near the California coast, leading to concerns about increased air pollution exposure of nearby communities. We use a combination of satellite-based observations from TROPOMI and ground-based observations from routine surface monitoring sites with chemical transport model results to analyze the changes in NO2 and PM2.5 in the Los Angeles Basin during a period in 2021 when the number of ships was at its peak. Using simulations to account for meteorological effects, changes are apportioned to emissions and meteorology. The largest emission-related changes in column NO2 occurred immediately east of the ports where emission-related NO2 increased by 28% compared to the baseline (2018-2019 average). In Central Los Angeles emission reductions led to a 10% decrease in NO2 during the same period. Emission-related PM2.5 increased by 0.7 µg/m3 on average with a maximum increase of 4.5 µg/m3. The emission/meteorology attribution method presented here provides a way to infer emission-influenced changes in air quality that are consistent with observations and suggests that both NO2 and PM2.5 were elevated in parts of the Los Angeles area during a period of increased port activity.

受新冠疫情相关供应链中断影响，洛杉矶港与长滩港的作业吞吐量提升、集装箱船舶积压严重，导致加州近岸海域船舶数量大幅增加，由此引发周边社区空气污染暴露风险上升的担忧。本研究结合TROPOMI卫星观测数据、常规地面监测站点的地面观测数据，以及化学传输模型（chemical transport model）的模拟结果，对2021年船舶数量达到峰值时段内洛杉矶盆地的二氧化氮（NO₂）与细颗粒物（PM2.5）浓度变化展开分析。通过模拟剥离气象因素的影响，将空气质量变化归因于排放与气象两大驱动因子。柱浓度二氧化氮（NO₂）中与排放相关的变化幅度最大的区域位于港口东侧紧邻区域，该区域与排放相关的二氧化氮浓度较基准期（2018-2019年平均值）上升28%。同期洛杉矶市中心区域因排放削减，二氧化氮浓度下降10%。与排放相关的细颗粒物（PM2.5）平均浓度上升0.7微克/立方米，最大增幅达4.5微克/立方米。本文提出的排放-气象归因方法，可用于推演受排放影响的空气质量变化，且该推演结果与观测数据吻合；研究结果表明，在港口作业繁忙时段，洛杉矶部分区域的二氧化氮与细颗粒物浓度均出现上升。