Impacts of Coronavirus-driven Reduction in Aerosols on Precipitation in the Western United States

Among the many impacts of COVID-19, the pandemic led to improved air quality conditions in the countries under quarantine. In particular, there was a remarkable reduction in aerosols due to the shutdown of industries and drastically reduced traffic in many Asian countries between late January and March 2020; similarly, California experienced a large reduction in aerosols due to the state’s lockdown in response to COVID-19. Meanwhile, the western United States, particularly the coastal areas from Washington to California, received much less precipitation than normal during the same period. Is it possible that this reduction in precipitation was driven by the reduced aerosols due to the coronavirus? Here we show that the reduction in aerosols resulted in higher temperatures (up to ~0.5℃) and generally lower snow amounts, but cannot explain the observed low precipitation amounts over this region. In addition to an assessment of the effects of coronavirus-related reduction in aerosols on precipitation across the western United States, our findings also provide basic information on the potential impacts different mitigation efforts aimed at reducing anthropogenic aerosols would have on the regional climate.

在新冠（COVID-19）大流行带来的诸多影响中，实施防疫管控的国家空气质量均得到显著提升。具体而言，2020年1月末至3月期间，众多亚洲国家因工业停产、交通流量骤减，气溶胶（aerosol）浓度出现大幅下降；与之类似，美国加利福尼亚州为应对新冠疫情实施封锁管控后，当地气溶胶浓度也显著降低。与此同时，美国西部地区，尤其是从华盛顿州到加利福尼亚州的沿岸区域，同期降水量较常年均值大幅偏少。那么，此次降水量偏少是否由新冠疫情引发的气溶胶浓度下降所导致？本研究表明，气溶胶浓度降低会使气温升高（最高可达约0.5℃），且积雪总量普遍减少，但无法解释该区域观测到的降水量偏少现象。除了评估新冠疫情相关的气溶胶浓度下降对美国西部降水的影响之外，本研究结果还为各类旨在降低人为源气溶胶（anthropogenic aerosol）排放的减排措施对区域气候的潜在影响提供了基础参考数据。