While there are no regulations or safe standards of PM1 or PM0.1, they can easily penetrate to lungs and block oxygen-blood exchange
Particulate matter (PM), which is the primary air pollutant in the Indian subcontinent, is mostly divided into two principal groups: coarse particles and fine particles. For regulatory purposes, PM is defined as either PM 2.5 (particles with a size of less than 2.5 µm), or PM10 (particles with a size of less than 10 µm). But, there exist no standards on ultra-fine particles, such as PM1 (size may range from less than 0.1 µm or 100 nano meter to 1 µm) and PM0.1, against which the natural defense system of the body usually fails.
The World Health Organization (WHO) too does not define acceptable standards for ultra-fine particles like PM1, which is 70 times thinner than a human hair. The WHO says, “These so-called ultrafine particles often contribute only a few per cent to the mass, at the same time contributing to over 90 per cent of the numbers.”
This is when the coarser particulate matter can usually be defended by the body. The hair in the nasal passage, along with the naturally occurring mucous of the nasal cavity, usually blocks the entry of these coarse particles. However, in the case of fine particles, these defenses usually fail, and the particles are able to penetrate into the nasal cavity all the way to the lungs, namely the bronchus and the bronchioles. From here, they have the potential to reduce the efficiency and block the alveolus, the minute grape-like chambers within the lungs that facilitate exchange of oxygen with blood.
These ultra-fine particles can be small enough to penetrate the body directly through the skin, via tiny pores meant for perspiration and other bodily functions. In fact, several studies have documented the direct correlation between skin conditions and prolonged exposure in industrial workers to ultra-fine particles.
PM1 can penetrate the cardiovascular stream even further, and give rise to lasting conditions, such as predisposing people to heart diseases. Ultrafine particles have been linked to delayed health effects including causing higher cardiovascular mortality. Studies in the west have also shown that PM1 can lead to premature births and affect foetal development.
Finely polluted India
In India, focus on PM10 and PM2.5 has led to action on certain kinds of sources of pollution that are perhaps more benign than they are made out to be. For instance, the various source apportionment studies for Delhi-NCR mention dust, including road dust to be the major contributor to PM2.5 and naturally occurring dust is made more toxic by ultra fine particles that coat them. These ultrafine particles are mainly produced by high temperature combustion, and recondensed organic and metal vapours. And thus, are commonly found in modern vehicular engines, as well as in certain industrial emissions.
The System of Air Quality and Weather Forecasting and Research (SAFAR) had, in 2016, analysed the concentration of PM1 in central Delhi, and recorded the average volume of PM1 during summer, winter and the monsoon at about 46, 49 and 20 micrograms per cubic metres. This accounted for 47 per cent of PM2.5 during winters, 44 per cent during summers and 61 per cent during monsoon.
The regulatory focus on PM2.5 has in the past misdirected policy efforts, diverting crucial resources and personnel to abating sources such as dust, which is a geographical feature of most cities in the subcontinent. Additionally, it enables other stakeholders responsible for high particulate emissions, such as vehicle manufacturers and industry associations to claim less responsibility than is due. There is a need for a regulatory focus on controlling ultrafine categories of PM.
However, since the BS VI emission standards have also included standards for particle numbers, vehicular emissions will not only be restricted in terms of the total mass of particulates they are permitted to contain, but also the total number of particles. So the total number of permissible ultra-fine particles will be restricted, if the regulatory tools are strong enough. But much more needs to be done to implement the laws that we already have.
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