We conducted this systematic review to identify and appraise studies investigating the coronavirus disease 2019 (COVID-19) effect on ambient air pollution status worldwide. The review of studies was conducted using determined search terms via three major electronic databases (PubMed, Web of Science, and Scopus) according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) approach. A total of 26 full-text studies were included in our analysis. The lockdown measures related to COVID-19 pandemic caused significant decreases in the concentrations of PM_2.5, NO₂, PM₁₀, SO₂ and CO globally in the range of 2.9%–76.5%, 18.0%–96.0%, 6.0%–75.0%, 6.8%–49.0% and 6.2%–64.8%, respectively. However, O₃ concentration increased in the range of 2.4%–252.3%. The highest decrease of PM_2.5 was found in 16 states of Malaysia (76.5%), followed by Zaragoza (Spain) with 58.0% and Delhi (India) with 53.1%. The highest reduction of NO₂ was found in Salé city (Morocco) with 96.0%, followed by Mumbai (India) with 75.0%, India with 70.0%, Valencia (Spain) with 69.0%, and São Paulo (Brazil) with 68.0%, respectively. The highest increase of O₃ was recorded for Milan (Italy) with 252.3% and 169.9% during the first and third phases of lockdown measures, and for Kolkata (India) with 87% at the second phase of lockdown measures. Owing to the lockdown restrictions in the studied countries and cities, driving and public transit as a proxy of human mobilities and the factors affecting emission sources of ambient air pollution decreased in the ranges of 30–88% and 45–94%, respectively. There was a considerable variation in the reduction of ambient air pollutants in the countries and cities as the degree of lockdown measures had varied there. Our results illustrated that the COVID-19 pandemic had provided lessons and extra motivations for comprehensive implementing policies to reduce air pollution and its health effects in the future.

我们进行了这项系统评价，以识别和评估 2019 年冠状病毒病 (COVID-19) 对全球环境空气污染状况影响的研究。根据系统评价和荟萃分析的首选报告项目 (PRISMA) 方法，通过三个主要电子数据库（PubMed、Web of Science 和 Scopus）使用确定的搜索词对研究进行综述。我们的分析中总共纳入了 26 项全文研究。与 COVID-19 大流行相关的封锁措施导致全球 PM _2.5 、NO ₂ 、PM ₁₀ 、SO ₂和 CO 浓度显着下降，范围为 2.9%–76.5%、18.0%–96.0%、6.0%–75.0 %、6.8%–49.0% 和 6.2%–64.8%。然而，O ₃浓度增加了2.4%–252.3%。 PM _2.5下降幅度最大的是马来西亚 16 个州（76.5%），其次是萨拉戈萨（西班牙），下降了 58.0%，德里（印度）下降了 53.1%。 NO ₂减少量最高的是萨累市（摩洛哥），达 96.0%，其次是孟买（印度），达 75.0%，印度达 70.0%，巴伦西亚（西班牙）达 69.0%，圣保罗（巴西）达 68.0% ， 分别。 O ₃增幅最高的是米兰（意大利），在第一阶段和第三阶段封锁措施期间分别增长了 252.3% 和 169.9%，加尔各答（印度）在第二阶段封锁措施期间增长了 87%。由于研究国家和城市的封锁限制，作为人类出行指标的驾驶和公共交通以及影响环境空气污染排放源的因素分别下降了30-88%和45-94%。 由于封锁措施的程度不同，各个国家和城市的环境空气污染物减少量存在很大差异。我们的结果表明，COVID-19 大流行为未来全面实施减少空气污染及其健康影响的政策提供了教训和额外动力。