24, 2020, so we used these date in our study. A comparison of air quality of monthly and daily averages of PM 2.5 concentrations and AQI was also performed for the four cities.
FIGURE 4 continued
Air Quality Index (AQI) Pre- and Post-Lockdown in the Selected Cities in Pakistan
Results
C: Peshawar
250
Air Quality of Selected Cities Figure 2 shows a comparison of the monthly average of PM 2.5 concentrations of the four cities. Lahore had the highest pollution lev- els. The data also showed a visible decline in concentrations during March 2020, prob- ably because people started practicing social distancing, activities were limited, and edu- cational institutions and offices were closed. The maximum decline was seen in April due to the enforced lockdown. The concentra- tions, however, were observed to rise in May 2020, which might be because the lockdown was eased.
Pre-Lockdown
Post-Lockdown
200
150
100
50
0
1/1/2020
2/1/2020 3/1/2020
4/1/2020
5/1/2020
6/1/2020
Date
D: Islamabad
Change in Air Quality Due to Lockdown
250
Post-Lockdown
Pre-Lockdown
200
Karachi In Karachi, reduction in PM 2.5 concentration (24-hr average) was observed post-lockdown. Average PM 2.5 concentration in the pre-lock- down period was 66.42 μg/m 3 , with a mini- mum concentration of 19.50 μg/m 3 and a maximum concentration of 151.32 μg/m 3 . Post-lockdown, however, the average con- centration decreased to 25.34 μg/m 3 (a 62% reduction), with a minimum concentration of 13.00 μg/m 3 and a maximum concentra- tion of 52.49 μg/m 3 . A strong negative corre- lation was found between time and PM 2.5 at p = .05. Figure 3A presents the change in PM 2.5 pre- and post-lockdown in Karachi. Corresponding to PM 2.5 , the AQI of Kara- chi also improved post-lockdown. Figure 4A presents the AQI pre- and post-lockdown in Karachi: the minimum AQI pre-lockdown was 67 (Moderate) and the maximum AQI was 202 (Very Unhealthy), with an average of 157 (Unhealthy). Post-lockdown, the minimum AQI was 83 (Moderate) and the maximum AQI was 143 (Unhealthy for Sensitive Groups), with an average AQI of 79 (Moderate). Lahore The data show improvement in air qual- ity of Lahore as PM 2.5 concentrations (24-hr average) decreased by 62% post-lockdown.
150
100
50
0
1/1/2020
2/1/2020 3/1/2020
4/1/2020
5/1/2020
6/1/2020
Date
ary 1, 2020, to June 9, 2020, for Karachi, Lahore, and Peshawar. 2. Invalid, missing, or erroneous readings were removed from the data. 3. A 24-hr average was calculated for each day. 4. The 24-hr PM 2.5 average was converted into an Air Quality Index (AQI) value. This conversion was performed using the U.S. EPA AQI calculator (www.airnow.gov). The raw PM 2.5 readings were converted to actionable information using the U.S. EPA NowCast algorithms. These algorithms use raw PM 2.5 readings and convert the readings into an AQI to inform health-related deci- sions (AirNow, 2020). The higher the AQI
value, the higher the pollution level and the higher risk to health (see U.S. EPA AQI lev- els at www.airnow.gov/aqi/aqi-basics). Linear regression was applied to find the statistical significance of the relationship between PM 2.5 concentrations and time. The same steps of data collection and analysis were repeated for each city. The results sec- tion presents the change in PM 2.5 concentra- tions and AQI of each city before and after lockdown. Restrictions in movements such as closure of educational institutions and self- social distancing started in all cities at the start of March 2020. Formal complete lockdown in the country, however, was enforced on March
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January/February 2023 • Journal of Environmental Health
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