Kathmandu, June 4 As Nepal is all set to celebrate the 35th World Environment Day tomorrow with ‘air pollution’ as its theme, the capital’s air quality has been labelled ‘unhealthy’ by the government. One of the yardsticks to measure air quality is PM2.5, which takes stock of concentration of particulate matters with diameter of less than 2.5 micrometres in the environment that can penetrate deep into the lungs even when one is wearing facial masks. These particulate matters mostly come from smoke emitted by vehicles and factories. The government has said that PM2.5 concentration above 40 microgram per cubic metre (m3) is ‘unhealthy’, whereas the World Health Organisation has set the threshold at 25 µg/m3. This morning, Pulchowk, for example, recorded PM2.5 concentration of 47.958 µg/m3, which is almost double the WHO standard. Pulchowk registered PM2.5 concentration of 64.60 µg/m3 on Friday, the highest in the past one week. The situation is pretty much the same in Ratnapark, Phora Durbar, Shankha Park, Bhaisipati, Maharajgunj and Bhaktapur, where air quality monitors have been placed. The PM2.5 concentration breached the government set standard at least once a day in the past six days in these locations. “The problem with tiny smoke particles (PM2.5) is that normal masks cannot prevent them from reaching the lungs. So, people exposed to this kind of environment for a long time gather large amount of unwanted elements in their blood. This develops respiratory problems and leads to failure of heart, kidney and other organs,” said Kedar Narsingh KC, a senior chest physician. The PM2.5 concentration level in the atmosphere can be controlled by reducing emission from vehicles and factories, according to KC. But vehicle emission check conducted by the Department of Environment in 2018 showed that 68 per cent of petrol-fuelled vehicles and 60 per cent of diesel-fuelled vehicles had failed the emission test. What is also worrying is that brick kilns operating in the valley have never been able to limit concentration of suspended particulate matter at 350 µg/m3, which is the standard set by the government. While PM2.5 concentration level in the valley is unhealthy, Kathmandu has made some progress in limiting the concentration of Total Suspended Particles, which measures concentration of all kinds of dust and smoke in the atmosphere. The national standard for TSP concentration is 120 µm (microns) per cubic metre. This threshold is more than double the standard of 50 µm/m3 set by the WHO. Air quality monitors showed that TSP concentration in the valley remained below 120 µm/m3 in the past six days. This is largely because of rains that the valley is getting. But the TSP concentration level can vary depending on the weather. For example, on one of the dry days in May 2018, Ratnapark recorded TSP concentration over 20 times the national standard. “But in recent months TSP concentration has fallen in the valley because roads that were demolished to lay water pipes have been blacktopped. Also, Phase I of the Ring Road expansion project has been completed,” said Prakash KC, environment inspector at the DoE. The DoE record of 2017 showed that construction projects contributed to 48 per cent of total air pollution in the valley, followed by transportation (28 per cent), brick kilns (eight per cent) and others. Air pollution is responsible for early deaths of seven million people worldwide every year, around 600,000 of whom are children, according to the WHO.