Restrictions enacted to reduce the spreading of COVID-19 have resulted in notably clearer skies around the world. In this study, we confirm that reduced levels of air pollution correlate with unusually high levels of clear-sky insolation in Delhi, India. Restrictions here were announced on March 19^th, with the nation going into lockdown on March 24^th. Comparing insolation data before and after these dates with insolation from previous years (2017 to 2019), we observe an 8.3% ± 1.7% higher irradiance than usual in late March and a 5.9% ± 1.6% higher one in April, while we find no significant differences in values from previous years in February or early March. Using results from a previous study, we calculated the expected increase in insolation based on measured PM2.5 concentration levels. Measurements and calculations agree within confidence intervals, suggesting that reduced pollution levels are a major cause for the observed increase in insolation.

为减少COVID-19的传播而采取的限制措施导致全世界的天空更加晴朗。在这项研究中，我们确认，印度德里空气污染水平的降低与晴空的异常高有关。限制措施是3月19^日宣布的，国家将于3月24^日锁定。比较这些日期前后的日照数据与往年（2017年至2019年）的日照数据，我们发现3月下旬的辐照度比平常高8.3％±1.7％，4月的辐照度比平常高5.9％±1.6％。与2月或3月初的往年相比，值存在显着差异。使用先前研究的结果，我们根据测得的PM2.5浓度水平计算了预期的日照增加量。测量和计算在置信区间内一致，这表明降低的污染水平是观察到的日照增加的主要原因。