4.1. Effectiveness of lockdown policy respond to diffusion of COVID-19
COVID-19 and its variants still brings bad effects on human life and health , economy and society  after more than one and half years science its firt reported case in Wuhan. There has been lots of variants, such as α-, ß-, γ-, δ-, ε-, λ-strains, etc.[19,20]. The spread and infection rates of δ(plus) -and λ-variants are more serious than the original ones. They are putting the world in a harsher state by bringing more deaths and severe cases. δ-variant was first found in Indian on 11th june 2020 and has been found in more than 130 countries. It has put Europe back on "war footing" . δ-variant is contagious with higher speed and short latent period. The proportion of δ-variant is more and more in the COVID-19  and can induced one more time death than other variants . Firstly detected in Argentina on November 8 2020, λ-variant with a simultaneous increase in infectivity and immune resistance has found in more than 30 countries . More and more aggrassive variants will be found as because of the rapid mutation nature of viruses. However, the existing vaccines are still effective against the new COVID-19 variants and can reduce rate of severe cases and deaths [23,25]. More than 1.1 billion doses of vaccines have been administered on the Chinese mainland by 26th July 2021 . Normally two shots are given to stop the infection, but a booster shot has begun to deal with these more aggressive viruses .
The lockdown policy with mask wearing is effective on stopping spread of the virus. lockdown policies including city-blocking and factory-shutdown could reduce the emission of air pollutants from transport and production [6,27]. As there were seldom heavy industry and traffic, enviroment during the lockdown peirod could be as basline without big human interference . It is good to natural enviroments, but people have to be blocked at home or somewhere else. They are unable to go out for work or communicate with others face to face, and living materials are limited. This may bring anxiety and depression to some people  and increase social instability . However, although China was seriously suffered from the virus, it responded quickly and effectively. The Chinese government took several steps to fight against the viruses. First, stopped traffic with latent infectivity and isolated suspected infection people. Second, disinfected, weared masks and kept enough distance. Third, banned parties, and asked people to eat at home with public chopsticks. Fourth, quickly set up enough health care stations and mobilized health care workers across the country to help COVID-19 patients everywhere. Fifth, tested nucleic acids ASAP to confirm the potential cases. Wuhan launched nucleic acid testing for all staff on 3rd August 2021. This got maximum identification of virus carriers, especially asymptomatic infected people . Sixth, worked overtime to develop vaccines and quickly distributed them free of charge across the whole country. All these measures are effective in protecting on human life and natural enviroment and made China fast block the spread of the virus and became the only country with positive economic growth in year 2020 although with a vast area and a large population. This undoubtedly reflects superiority of the system, Chinese kindness and obedience to orders in pulling together to get through the tough times. All the measures still work in fighting against δ-, γ- and other new potential variants in the future. The COVID-19 outbreak has hit the world, especially with serious impact on human life and the world economy. Nevertheless, it also provided precious chances for people to rethink the value of life: We should sustainablely develop and pursuing spiritual instead of excessive material enjoyment. This can sustain a good natural enviroment and help build sustainable socities [6,7]. The earth is our only home, and we are all in the same boat. We should work together to fight against the viruses and protect the earth environment. It can sustain a healthy living enviroment and the ultimate benefit is human beings.
4.2. Changes of major pollutants in Wuhan compared with other cities in the world duiring COVID-19
Air pollution can increase COVID-19 incidence and deaths [4,9]. Released from tailpipe, NO2 and PM2.5 increases the risk of lung infections [4,12]. Besides, NO2 may be an important trigger of mental disorders  and acidity of PM2.5 penetrates the lower airways linking to respiratory and cardiovascular disease [4,28]. SO2 mainly from the heavy industry with fossil as fuels [1,28]. Whereas, NO2, PM2.5 and PM10 in wuhan were from similar sources, including both heavy industry and traffic. This is different from those in Shanghai (Fig. S3): PM were mainly from the north of Yangzi Delta area [1,30].
Comparatively, Shanghai did better in controling all the five air pollutants, which sharply decreased compared with those in Wuhan (Fig. S3). It's worth noting that O3 also showed a decreasing rate of 46%. Comaratively, O3 in wuhan increased by 26%. It's worth noting that surface O3 is always a serious pollutant in developing contries compared with those in the USA . Decreasing concentration of NO2 (45%) in Wuhan is lower than those (64%) in Shanghai (Fig. S3), and Delhi (60%) and Mumbai (78%) in Indian , but higher than other Chinese cities (16-38%) [6,31], most cities in Spain (30%) , the South East of the UK (38%)  and Almaty while (35%) in Kazakhstan .
Generally, the controlling of air major pollutants in Wuhan cannot be lasted for long when the city was unlocked reflected by the increasing AQI (Fig. 3). Besides the reopening of some factories and unlimitation of traffic, its location is another important reason. Wuhan is a transportation hub in central China, pollutants can reach there from regions around it. So, Wuhan did well in controlling the viruses and pollutants with consideration of its location.