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To prevent the transmission of the novel coronavirus disease 2019 (COVID-19), China adopted nationwide lockdown measures on January 25, 2020, leading to an evident diminution in the observed air pollutants. To investigate the influence of the lockdown on atmospheric chemistry, the specific molecular composition, oxidative potential of organic aerosols (OAs) in PM2.5 were studied using a high-resolution orbitrap mass spectrometry at a typical coal-combustion city, Linfen, in the North China Plain (NCP). The major air pollutants including PM2.5, PM10, SO2, NO2, and CO were observed to be diminished by 28.6–45.4%, while O3 was augmented by 52.5% during the lockdown compared to those before the lockdown. A significant decrease of oxygen-containing (CHO) compounds (24.7%) associated with anthropogenic acids was observed during the lockdown, implying a reduction in fossil fuel combustion. The coal-burning related sulfur-containing organosulfates (CHOS-) and nitrooxy-sulfates (CHONS-) have also shown attenuated in both their relative abundances and anthropogenic/biogenic ratios. Amine/amide-like CHON + components have decreased by 27.6%, while nitro/nitrooxy-containing CHON- compounds have only decreased by 7.1%. Multi-source nitrogen-containing (CHN) compounds have shown a moderate elimination of 24.0%, while the identified high-condensed azaarenes have fallen from 17.7% to 14.7%, implying a potential reduction in the health risk of OAs during quarantine. The measurement of OAs’ oxidative potential through dithiothreitol (DTT) assay has confirmed that as it had dropped from 0.88 nmol min−1 m−3 to 0.80 nmol min−1 m−3. High correlations were observed between the abundance of OA subgroups with the concentration of PM2.5 after the execution of the lockdown, suggesting a potential elevation in the contribution of organic components to the total PM2.5 level. Our study provides insightful compositional and health-related information in the variation of OAs during the lockdown period and attests to the validity of joint-control strategy in controlling the level and health risks of numerous atmospheric pollutants.

Background During the COVID-19 epidemic period, people showed a stronger connection to the environment within their communities. Although tree canopy in residential areas has been shown to positively affect psychological distress, it is not clear whether the COVID-19 epidemic played a role in this process. Elucidation of the relationship between tree canopy and the impact on psychological distress during the COVID-19 epidemic could provide valuable information as to the best methods to help individuals cope with urban mental stress events. Methods A total of 15 randomly selected residential areas of Beijing were enrolled in this repeated cross-sectional study. A total of 900 residents were included in the two-waves of the investigation (450 residents per wave) before and during the COVID-19 epidemic (i.e., May 2019 and May 2020). Psychological distress was estimated using the 12-question General Health Questionnaire (GHQ-12). Tree canopy coverage (TCC) was measured through visual interpretation based on the 2013 data sources (World View 2 satellite imagery of Beijing urban areas with a resolution of 0.5 m). The demographic characteristics, distance to the nearest surrounding green or blue space, residential area house price, household density, and construction year were also collected in this study. A multivariate logistic regression, relative risk due to interaction (RERI), and synergy index (SI) were used to explore the relationships among tree canopy, COVID-19, and psychological distress. Results The negative impact of the COVID-19 epidemic on mental health was significant, with the prevalence of psychological distress increased 7.84 times (aOR = 7.84, 95% CI = 4.67–13.95) during the COVID-19 epidemic period. Tree canopy coverage in the group without psychological distress was significantly higher than that of the psychologically distressed group (31.07 ± 11.38% vs. 27.87 ± 12.97%, P = 0.005). An increase in 1% of TCC, was related to a 5% decrease in the prevalence of psychological distress (aOR = 0.95, 95% CI = 0.93–0.98). An antagonism joint action between tree canopy and the COVID-19 epidemic existed (RERI = 1.09, 95% CI = 0.72–1.47; SI = 0.16, 95% CI = 0.05–0.52), and persisted enhancing only in medium (26.45%–33.21%) and above TCC level. Correlation of GHQ items and TCC significantly differed between the COVID-19 non-epidemic and epidemic periods, with the effects of tree canopy on GHQ-12 items covering topics, such as social function and depression, presumably absent because of epidemic limitations. Conclusions This study indicates that the COVID-19 epidemic harmed mental health and verified the positive effects of residential tree canopy on psychological distress in Beijing. We suggest paying more attention to residents in areas of low TCC and dealing with psychological distress caused by public health stress events based on tree canopy strategies.

Coronavirus disease (COVID-19) spread across the globe through the human transmission. The World Health Organization suggested social distancing to curb the community spread. After national social lockdown started in India, air quality improved drastically. This further hypothesized to influence the environment and human health, and this study is positively the first to weigh it using multiple indices. The calculated environmental indices are photochemical ozone creation potential (POCP), acidification potential (AP), and eutrophication potential (EP). The cancer risk, chronic health index (CHI), and acute health index (AHI) were considered to calculate the health risk. The spatial trend change in the air pollution reflecting on these indices are calculated for four Indian megacities Delhi, Bangalore, Hyderabad, and Kolkata. Temporal variation was accounted for monthly (2019 vs 2020), one-week and two-weeks period during the social lockdown. The results showed a significant decrease in environmental and health risk during the lockdown due to a corresponding decrement in air pollution. The decrease in the particulate matter was found to play a vital role in altering the air pollution mediated risks of interest. Delhi showed a maximum difference in POCP and Acute HI by recording a dip of 70.79% and 43.53% respectively in 2020 during lockdown. The maximum reduction in health risk indices was 41%, 31%, 17%, 19% for Delhi, Bangalore, Hyderabad, and Kolkata. Bangalore recorded the maximum decline in EP, Cancer risk, Chronic HI by 66.66%, 58.62%, and 58.76% in 2020 compared to 2019. A maximum fall in AP was seen in Kolkata by 57.23% in 2020 among all cities. The connection between these drop-in indices and the cause of air pollutants were well discussed. This present paper gives more in-depth insights into air pollution's effect on environmental and health parameters by connecting and converging various air pollution aspects into a single scale. This study also enlightens the importance of controlling air pollution to have a better environment and healthy life to attain sustainable development., Graphical abstract Conceptual illustration of impact of COVID-19 enabled social lockdown on environmental and health risk indices in India.Image 1