Coronavirus, lockdowns, and air quality

Worsening air quality demands efficient air monitoring utilising both remote sensing tools and ground-level sensors

Muhammad Zaheer/Adnan Yousaf January 17, 2021


According to the World Health Organization (WHO), 92% of the world’s population lives in places where air pollution is exceeding the defined limits. Among other pollutants, elevated levels of particulate matter — i.e. dust, smoke, etc — in ambient outdoor air are the primary cause of mortality worldwide. Pakistan’s urban areas have been among the most polluted in the world, and the situation worsens after the harvesting season carried out in mid-October. During this season, hospitals observe more patients with problems related to respiration and eye irritations. Low visibility has resulted in many highway car accidents in areas heavily blanketed by smog.

We analysed air quality data (May 2019-November 2020) from the air quality monitoring stations (AQMS) installed at the US consulates in Karachi, Lahore, Islamabad and Peshawar so as to see the impact of Covid-19 on air quality during lockdowns. Levels of particulate matter with a diameter of 2.5 microns (PM2.5) were used to calculate the air quality index (AQI).

Air quality remained good (less than 50) during April through September 2020 in Karachi and Islamabad. However, Lahore and Peshawar observed low air quality the whole year. On average, AQI in both cities remained above 100, which meant unhealthy air for children, older people, and people with respiratory and cardiovascular diseases.

As compared to last year, AQI has been lower from May to September this year, which could be due to the lockdown and reduction in construction, automobile transport, and low industrial activity. For instance, in May only 40, 30, 30, and 26% reduction in PM2.5 levels were observed for Lahore, Islamabad, Karachi, and Peshawar, respectively.

We also obtained satellite data from NASA which measures particulate pollution in Aerosol Optical Dispersion (AOD) and shows the extent to which aerosols block sunlight from reaching the ground. An AOD value of 0.01 means a clean atmosphere, and a value of 0.4 will correspond to a very hazy atmosphere with loads of dust, smoke, and pollution.

Comparing the time-averaged AOD maps for lockdown dates (March 24 to May 9) shows no significant air quality difference for 2019 and 2020. For instance, most of Punjab and Sindh (except Karachi) provinces have been unhealthy for sensitive groups during the lockdown. During the same period in 2019, it has been better in southern Punjab with moderate air pollution.

Nitrogen dioxide is another essential atmospheric pollutant produced by automobiles and other fossil fuel burning processes. It is known to worsen respiratory diseases and enhance asthmatic attacks. A reduction in NO2 levels was observed during the lockdown period, which was expected due to no or little vehicular activity during the lockdown.

Since October, PM2.5 levels have gone high in all four cities compared to the last year. For instance, during October 2020, a 60% and 27% increment in PM2.5 levels was observed for Lahore and Peshawar, respectively. On the other hand, Islamabad and Karachi showed only an 11% and 16% rise, respectively. This is when Pakistan is observing the second wave of Covid-19. A recent study has shown that long-term exposure to air pollution increases the severity of Covid-19, leading to an increased mortality rate.

Worsening air quality demands efficient air monitoring utilising both remote sensing tools and ground-level sensors. An economical way of doing this could be establishing a hyperlocal network of low-cost sensors to collect street-level air quality data almost real-time. Emission values from low-cost sensors can be compared and corrected against the reference. Thus, high quality and reliable air quality data could be obtained that would help in policymaking and legislation.


Published in The Express Tribune, January 18th, 2021.

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