ADVANCEMENT OF THE SCIENCE
In the pre-lockdown period, the minimum PM 2.5 concentration was 20.30 μg/m 3 and the maximum PM 2.5 concentration was 340.36 μg/m 3 , with an average PM 2.5 concentration of 132.00 μg/m 3 . Post-lockdown, the mini- mum PM 2.5 concentration was 15.00μg/m 3 and the maximum PM 2.5 concentration was 139.00 μg/m 3 , with an average concentration of 50.52 μg/m 3 . A strong negative correlation was found between time and PM 2.5 at p = .05. Figure 3B shows PM 2.5 concentrations pre- and post-lockdown in Lahore. Similarly, the AQI was observed to improve post-lockdown. The minimum AQI pre-lock- down was 68 (Moderate) and the maximum AQI was 390 (Hazardous), with an average AQI pre-lockdown of 190 (Unhealthy). In the post-lockdown period, the minimum AQI was 57 (Moderate) and the maximum AQI was 194 (Unhealthy), with an average AQI improved to 138 (Unhealthy for Sensitive Groups). Figure 4B presents the AQI pre- and post-lockdown in Lahore. Peshawar In Peshawar, the data also show an improve- ment in air quality post-lockdown. In the pre- lockdown period, the minimum PM 2.5 concen- tration was 20.70 μg/m 3 and the maximum PM 2.5 concentration was 155.10 μg/m 3 , with an average PM 2.5 concentration of 86.07 μg/m 3 . Post-lockdown, theminimum PM 2.5 concentra- tion was 16.50 μg/m 3 and the maximum PM 2.5 concentration was 63.75μg/m 3 , with an aver- age PM 2.5 concentration of 36.72 μg/m 3 . This finding shows a 57% reduction in PM 2.5 con- centration post-lockdown. A strong negative correlation was found between time and PM 2.5 at p = .05. Figure 3C presents the PM 2.5 concen- tration pre- and post-lockdown in Peshawar. Similar to PM 2.5 , the AQI also improved post-lockdown in Peshawar. The AQI improved from 167 (Unhealthy) pre- lockdown to 104 (Unhealthy for Sensitive Groups) post-lockdown. Pre-lockdown, the minimum AQI was 69 (Moderate) and the maximum AQI was 200 (Unhealthy). Post-lockdown, the minimum AQI was 60 (Moderate) and the maximum AQI was 155 (Unhealthy). Figure 4C presents the change in AQI post-lockdown in Peshawar. Islamabad In Islamabad, the data show improved air quality post-lockdown. The minimum PM 2.5
concentration was 15.79 μg/m 3 and the maxi- mum PM 2.5 concentration was 170.66 μg/m 3 , with an average PM 2.5 pre-lockdown of 61.43 μg/m 3 . Post-lockdown, the minimum PM 2.5 concentration was 24.66μg/m 3 and the maxi- mum PM 2.5 concentration was 38.00μg/m 3 , with an average of 27.42 μg/m 3 . This finding shows an approximately 55% reduction in PM 2.5 post-lockdown. A strong negative cor- relation was found between time and PM 2.5 at p = .05. Figure 3D presents PM 2.5 concentra- tion in the periods pre- and post-lockdown in Islamabad. Corresponding to PM 2.5 , the AQI also improved due to lockdown. Pre-lockdown, the minimum AQI was 59 (Moderate) and the maximum AQI was 221 (Very Unhealthy). Post-lockdown, the minimum AQI was 77 (Moderate) and the maximum AQI was 107 (Unhealthy for Sensitive Groups). The aver- age AQI improved from 154 (Unhealthy) pre- lockdown to 83 (Moderate) post-lockdown. Figure 4D presents the change in AQI due to lockdown in Islamabad. Discussion and Conclusion Our study focused on identifying the change in air quality pre- and post-lockdown in four cities of Pakistan using PM 2.5 concentrations (24-hr average) and AQI levels from Janu- ary 1, 2020, to June 9, 2020. We also com- pared the air quality of these cities. We found Lahore to have the highest air pollution both pre- and post-lockdown among the four cit- ies studied. Air quality of all the cities was observed to improve following lockdown. Average PM 2.5 concentration in the post- lockdown period decreased (statistically significant) by >50% compared with the pre- lockdown concentration in all four cities. For PM 2.5, a 62% reduction was observed in Kara- chi and Lahore, followed by 57% in Peshawar and 55% in Islamabad. The average AQI improved from Unhealthy to Moderate in Karachi and Islamabad and from Unhealthy to Unhealthy for Sensitive Groups in Lahore and Peshawar. Although people started restricting their activities at the beginning of March 2020 and govern- ment enforcement of restrictions was also slowly ramping up, on March 24, 2020, a complete lockdown was enforced that was then eased around May 10. Lockdown, how- ever, was not completely lifted and smart lockdown was in place in various cities and
in various phases. All restrictions related to COVID-19 were finally removed in March 2022. Thus, a decline in PM 2.5 concentrations and improved AQI was observed since the start of March 2020. A maximum improvement in air quality was observed in April 2020 when complete lockdown was enforced. In May, as restric- tions were eased, PM 2.5 started increasing. The PM 2.5 concentrations were still less compared with the pre-lockdown period because smart lockdown was in place. Our study shows how reduced transportation and closure of industries led to improvement in air quality. This finding is comparable to studies in other countries that examined improvement of air quality caused by COVID-19 lockdowns. We understand that our study has limi- tations. This study is compromised by the availability of data. We considered only one parameter to evaluate air quality. Compari- son of air quality data with the same time the previous year, however, could not be done due to the unavailability of data. Also, our study did not take into consideration seasonal variations. Moreover, the data gath- ered by the U.S. Embassy and Consulates in the four cities were from a single monitoring station, which might not be representative of the entire city. This article, however, serves as a baseline for research in Pakistan on air quality and the e£ect of COVID-19 lockdowns. Further research is needed to identify changes in air quality after lockdown has been lifted. One key aspect of air pollution that needs further evaluation is that the mortality rate of COVID-19 is higher for people who also have cardiovascular illness or chronic respiratory illness. These diseases are linked to air pollu- tion, which implies that air pollution can be a secondary factor for mortalities associated with COVID-19. A study by Zhu et al. (2020) showed a relationship between high air pol- lutant concentration and high probability of COVID-19 cases. Viruses are one of the smallest aerosol particles, with a diameter as small as 20 nm. Viruses are not usually airborne themselves, but rather they attach to other suspended particles (e.g., PM 2.5 ). Thus, the concentra- tion of air pollutants such as those of PM 2.5 and PM 10 a£ect the transmission of SARS- CoV-2. Smaller particles remain suspended in air for longer time periods because of their
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