*3.3. Trends of Air Pollutants in China before and after the Pandemic*

The overall air quality change in 50 days (Table 1) reveals that Harbin recorded the highest reduction (43%) in air pollutants followed by Guangzhou (42%), Wuhan (36%), Jinan (33%), Chengdu (32%), Nanjing (31%), Shanghai (30%), Zhengzhou (29%), Xian (25%), Xiamen (23%), Chongqing (23%), Lanzhou (17%), and Anshan (4%). The most interesting fact in this analysis is that when all the cities were experiencing improved air quality, Beijing recorded deteriorating air quality; it recorded a 34% increase in air pollutants during the 50-day study period after lockdown. In this context, it is important to look into the individual pollutants in detail for an insight into understanding their roles in determining air quality.

**Table 1.** Temporal change in air pollutants of 14 cities of China before (4 December 2019 to 22 January 2020) lockdown and after lockdown (23 January to 12 March 2020). The 100-day daily average concentration in total and change in percentage. Total 6 pollutants NO2, O3, PM10, PM2.5, SO2 (μg/m3), CO (mg/m3) including AQI (change in percentage).


Source: Arranged by author, Ministry of Environmental Protection of China (MEPC), China Ministry of Ecology and Environment, 2020.

During the 50 days of study after lockdown, the concentration of carbon monoxide (mg/m3) reduced by 40% in Lanzhou, 37% in Jinan, 31% in Zhengzhou and Chengdu, 30% in Harbin, 29% in Nanjing, 28% in Xian, 27% in Xiamen, and 25% in Guangzhou (Figure 8b). The temporal changes in NO2 (Figure 8c) reveal that the more than 50% concentration of NO2 has reduced in Wuhan (63%), Chengdu and Guangzhou (55%), Zhengzhou (53%), Jinan, Nanjing and Shanghai (52%) while, other cities received below 50% NO2 concentration (ranging between 20% and 49%).

On the other hand, the results displayed a drastic rise in ozone in the atmosphere in almost all cities after the lockdown. The detailed analysis of O3 (Figure 8d) explained that Xian experienced a 200% rise in O3. Moreover, most of cities experienced more than 100% escalation of O3, for instance, Zhengzhou (155%), Jinan (149%), Wuhan (147%), Chongqing (145%), Nanjing (122%), Chengdu (120%), and Harbin (118%). Interestingly Beijing, the city where the overall quality of air has declined, also experienced a high rise in O3 (95%). In addition, the concentration of ozone has also increased in Shanghai (81), Lanzhou (81%), and Anshan (57%). Cities such as Xiamen and Guangzhou experienced only 17% and 13% increases in O3, respectively.

**Figure 8.** Temporal change in air quality of China before and after lockdown. Total 100-day daily average data, 4 December 2019 to 22 January 2020 (before lockdown) and 23 January to 12 March 2020 (after lockdown). (**a**) Air Quality Index; (**b**) CO; (**c**) NO2; (**d**) O3; (**e**) PM10; (**f**) PM2.5; (**g**) SO2. Source: Ministry of Environmental Protection of China (MEPC), China Ministry of Ecology and Environment, 2020 and OMI, Global Modeling and Assimilation Office, NASA.

The temporal change in PM10 (μg/m3) (Figure 8e) reveals its sudden decrease in all cities except Beijing after the lockdown (Table 1). The maximum decrease in PM10 concentration was observed in Guangzhou (56%) followed by Wuhan and Harbin (45%). The other cities that observed a substantial decrease in PM10 are Nanjing and Jinan (37%), Chengdu

(36%), Shanghai and Xiamen (29%), Xian (28%), and Zhengzhou (26%). Conversely, PM10 concentration increased by 4% in Beijing after the lockdown. Like PM10, the concentration of PM2.5 also considerably decreased after the pandemic lockdown (Figure 8f). The cities which observed low concentrations of PM2.5 are Harbin (47%), Guangzhou (43%), Wuhan (39%), Jinan and Chengdu (37%), Nanjing (36%), Shanghai and Lanzhou (34%), Zhengzhou (32%), Xiamen (31%), and Xian (30%). Simultaneously, Beijing experienced a very high concentration of PM2.5 (43%) after the lockdown.

Along with other pollutants, the temporal change in SO2 concentration (Figure 8g) displays a substantial decrease in all cities after the lockdown. The cities that experienced a high proportion decrease in SO2 concentration are Lanzhou (39%), Jinan (38%), Guangzhou (36%), Nanjing (31%), Shanghai (27%), Xian (26%), and Chongqing and Harbin (25%) (Table 1).

The daily average concentration of air pollutants for 100 days (50 days before lockdown and 50 days after lockdown) of 14 cities (Figure 9) reveals that the air quality has remarkably improved in Guangzhou where 43% of pollutants have declined during this study period. The concentration of PM10 and NO2 has reduced by 56% and 55%, respectively. Similarly, in Shanghai, the overall pollutants in the atmosphere have decreased by 30% (Table 1). In Nanjing, the overall air quality (AQI) has improved by 31%. Moreover, the air quality of Xiamen has improved by 23% and the concentration of NO2 and PM2.5 has declined by 49% and 31%, respectively. In Jinan, the overall air quality has improved by 33% and the NO2 concentration has decreased by 52%. However, the concentration of O3 has amplified by 149%. In Zhengzhou, the concentration of NO2 has reduced by 53% and the concentration of O3 has grown by 155%. In Wuhan, the major pandemic affected area, the concentration of NO2 has reduced by 63% and PM10 by 45% whereas the concentration of O3 has increased by 147%. The air quality has also improved in Harbin where the concentration of NO2 has reduced by 49% and the concentration of O3 has increased by 118%. In Chongqing, the concentration of NO2 has reduced by 47% and the concentration of O3 has improved by 145%. Similarly, in Chengdu, there has been a 55% reduction in NO2 concentration and a 120% increase in O3 concentration in the atmosphere. In Xian, there is a 47% change in NO2 and a 200% increase in O3 in the atmosphere. In Anshan, the concentration of NO2 has reduced by 29% whereas the concentration of O3 has increased by 57%.

**Figure 9.** *Cont*.

**Figure 9.** The daily average concentration of air pollutants in 14 cities of China. The 100 days (50 days before lockdown and 50 days after lockdown. NO2, O3, PM10, PM2.5, SO2 (μg/m3), and CO (mg/m3): primary vertical (left) and AQI shown in secondary vertical (right). Source: Ministry of Environmental Protection of China (MEPC), China Ministry of Ecology and Environment, 2020.
