How is Air Pollution Measured?

Kathmandu: Known for being one of the most polluted cities, Kathmandu often finds itself in the top 10 lists globally. Recently, there was talk about washing vehicles entering the valley to curb air pollution. While this was discussed as a solution, especially for vehicles coming from other districts, it has remained just that—talk.

Inside Kathmandu, vehicles remain a major source of pollution. Along with traffic, construction activities, industrial processes, wildfires, cross-border pollution, and other factors all contribute to the city's worsening air quality, according to the Department of Environment.

Air quality is currently being monitored at seven stations across the valley, including areas like Dhulikhel, Bhaktapur, Shankhapark, Ratnapark, Khumaltar, Kirtipur, and Bhaisepati. These stations help measure pollution levels.

How is Air Pollution Measured?

The government set national air quality standards in 2069 BS (2012 AD), with nine parameters used to gauge the quality of the air. Across the country, there are 27 real-time air quality monitoring centres, set up by the Environment Department. These centres have instruments that measure particles in the air, such as PM1, PM2.5, PM10, and TSP (Total Suspended Particles).

Some of the centres also measure gases like carbon monoxide and ozone. According to Department Information Officer Deepak Gyawali, the stations operate automatically to monitor air quality.

The study reveals that in almost all the stations, the amount of PM2.5, which consists of tiny particles that can easily enter the human lungs and cause respiratory diseases, frequently exceeds the national standards. This indicates the severity of the pollution. PM2.5 and PM10 pollution levels are usually higher in the mornings and evenings, while TSP levels peak during the day.

As per the Environment Bulletin of May 2024, except for a few days, the daily average PM2.5 levels from January 1 to April 15 were above the government's set standards. Pollution saw a drop in March, but it rose again significantly in April.

Why is Pollution Higher at Certain Times?

Air pollution levels often depend on the weather. Experts explain that winter rainfall patterns also affect how much pollution occurs. Pollution is generally higher in January and February, partly due to lower temperatures. When temperatures are low, the air near the ground can’t rise as easily, trapping pollutants close to the surface.

This creates what’s known as an "inversion effect," where a layer of cold air near the ground is capped by warmer air above, acting like a lid and keeping pollution trapped close to the ground. This is why air pollution spikes during this time.

As temperatures rise in February and March, pollution levels start to decline. However, as wildfires increase across the country in the summer months, air pollution once again rises.