Satellite images and air quality index (AQI) data indicate that the improvement in China's air quality as a result of recent lockdowns and industrial stoppages related to the Covid-19 pandemic may have been a temporary phase as the country gets back to work. Nitrogen dioxide (NO2), which is produced by combustion engines and burning fossil fuels, fell in Wuhan – the early Covid-19 epicentre in China – during the 20-day period starting January 21 compared with the previous 20-day cycle, according to a coloured satellite map compiled by the European Environmental Bureau (EEB), a regional network of environmental organisations. But after Wuhan lifted its lockdown in early April and Beijing downgraded its emergency response level last month, NO2 levels increased again. The Chinese authorities blocked people from leaving or entering Wuhan on January 23 and NO2 levels remained static at lower levels: below 150 micromoles per square metre (umol/m2) until late March. But during the 20-day period that ended April 9, a day after the lockdown was cancelled, levels spiked back to about 300 umol/m2 in the most polluted areas of the city, the EEB map shows. A similar pollution curve can be seen for areas surrounding Beijing, Shanghai and Guangzhou, according to the EEB map. Higher Covid-19 toll in pollution hotspots points to environmental factor In January, when the Covid-19 outbreak was just beginning, levels of the most harmful atmospheric particulate matter (known as PM2.5) were relatively higher than in the following three months. For example, during this period Beijing saw five days of PM2.5 levels between 200 and 300, deemed as very unhealthy, while only two days between 25 and 50, which indicated good air, according to aqicn.org, an AQI aggregator of various local observer and monitor sources. In February, PM2.5 levels in Beijing significantly improved, with only three days of “very unhealthy” air and six days of “good air”. There were no “very unhealthy” days in March and April. However, in the first seven days of May, as social activities picked up during the five-day Labour Day holiday, there have so far been no “good” air quality days, according to aqicn.org. “During this pandemic, what happens in China has often been a window for what happens elsewhere some time later,” warned EEB air policy officer Margherita Tolotto, who called for action in other regions, such as in Europe, from repeating China's story. Why there’s an upside to coronavirus crisis for stargazers In Milan, Italy – one of the worst affected areas in Europe by the pandemic – PM2.5 levels were also much lower between March and May, compared with the first two months of the year, according to aqicn.org data. Milan had 13 unhealthy days in January and three in February, but no unhealthy air starting March (when the coronavirus led to lockdowns and social distancing measures) and the number of days with “good” and “moderate” air significantly increased. However, Milan has announced an ambitious project to reduce car use as lockdowns are lifted, and aims to transform 35 kilometres of roads into cycling and walking spaces.