Smog might have disappeared, but the air quality of Lahore, and Punjab, continues to be unhealthy at the very least. According to AirVisual’s (a crowd-sourced air quality community) readings, the Air Quality Index (AQI) for Lahore has been among the worst cities around the globe, falling close to those of Dhaka and Beijing. Even these days when the smoggy/foggy conditions have waned, the air quality around Lahore is daunting, mostly juggling for a position between hazardous and unhealthy.
Running its fifth consecutive year into smog, Lahore has the worst air quality in Pakistan with annual average PM2.5 conc. of 116 ?g/m³ for 2017, which is 11 times the WHO guidelines and three times the safe limits for yearly exposure as defined in Pakistan’s National Environmental Quality Standards (NEQS).
BR Research’s column, ‘Skepticism and misty air quality’, published on Jan 02, 2018, talked in detail about smog in Lahore and what needs to be done. Let's look at Lahore's air quality from a comparative lens. Karachi’s air quality also suffers from high levels of particulate matter PM2.5. According to PAQI, the air quality there has also been three to five times above the safety levels. However, surprisingly Karachi’s AQI has been faring a lot better than that of Lahore. Unbelievable for many, Karachi – a city in shambles - has been falling in the moderate category in a randomly taken time slot. Why the difference?
To find out the answer to this question, BR Research contacted Pakistan Air Quality Initiative (PAQI) - community-driven initiative to set up low-cost, real-time monitors to capture air quality data and thereby increase social awareness. One key reason that was brought to light was the concept of ‘temperature inversion’. Inversion plays an important role in disturbing air quality of an area where it exists as the pollutants stay trapped within the lower atmosphere, and cannot escape from the area. Lahore’s (and Punjab’s) air quality is extremely bad in winters from October through till February because of this temperature inversion. Also, other seasonal effects of crop-residue burning contribute heavily during this season. Moreover, Punjab also has a number of brick-kilns that contribute heavily throughout the year to air pollution.
On the other hand, while Karachi has its own set of pollutants like water, sewerage etc., it does not have this temperature-inversion effect that causes extremely high air pollutant contents. Also, it does not have crop-residue burning or brick kilns. Basically, there are fewer sources of air pollution there, combined with a greater dilution effect of the sea breeze.