Outdoor air purifiers are not the solution to Delhi’s Air Pollution Problem

This story was originally written by Ashutosh Thakur (CEO, Schillings Air). Adding few excerpts here for the readers:

Why we avoided creating humongous towers of air purifiers in Delhi

Before we describe why trying to clean ambient air through humongous air purifiers is a futile exercise, let’s familiarize ourselves with two technical terms we’d be using frequently in this article- HEPA, and Particulate Matter.

1. High Efficiency Particulate Air” or “High Efficiency Particulate Arrestance.” This acronym refers to a filter that is manufactured, tested, certified, and labeled in accordance with current HEPA filter global standards.

HEPA filters are composed of a mat of randomly arranged fibres. The fibers are typically composed of fiberglass and possess diameters between 0.5 and 2.0 micrometers. Key factors affecting its functions are fibre diameter, filter thickness, and face velocity. The air space between HEPA filter fibers is typically much greater than 0.3 μm.

Sources: (https://en.wikipedia.org/wiki/HEPA(2018))

2. Particulate air pollution is a mixture of solid, liquid or solid and liquid particles suspended in the air. These suspended particles vary in size, composition and origin. It is convenient to classify particles by their aerodynamic properties because: (a) these properties govern the transport and removal of particles from the air; (b) they also govern their deposition within the respiratory system and © they are associated with the chemical composition and sources of particles. These properties are conveniently summarized by the aerodynamic diameter , that is the size of a unit-density sphere with the same aerodynamic characteristics. Particles are sampled and described on the basis of their aerodynamic diameter, usually called simply the particle size.

Sources: (Health Aspects of Air Pollution” (2003), Chapter 5 Particulate matter (PM), Section 5.1 Introduction)

Let’s find out how an Air Purifier Works.

Air purification is a system in which the air is passed through a filter (HEPA), which releases an output of clean air. The level of cleanliness depends on the air pressure, and the grading of HEPA.

However, the level of cleanliness and size of the area cleaned through this system also heavily relies on the capacity of the fan. Since, it’s the fan which draws air and forces it through HEPA, thus, trapping particulate matter and releasing clean air as output. The size of the area in which we use this system also dictates heavily the quality of air as output. Larger the fan, more is the output of the clean air.

However, just as it is impossible to clean water by installing water purifiers in the middle of the ocean, it is also unadvisable to try to clean air through installing large fans and HEPA filters to clean ambient air.

The predominant reasons we cannot and should not influence the air quality in outdoor situation is because:

1. The rate of cleaning the air will be always slower than the mixing of cleaned air with the polluted ambient air.
2. One of the main characteristic of air is that it’s mobile, and unless used in a closed space, the air purifier will be repeatedly cleaning the same polluted air due to mixing of clean air with the polluted air.
3. HEPA is not washable. The pleating of HEPA is dense and the material used is fragile which makes it impossible to be washed and reused. The amount of pollutants being passed through HEPA in ambient air will be high and thus the choking of the filter will happen at a much faster rate resulting in requirement of frequent replacement of HEPA filters.
4. The non biodegradable HEPA will become another source of pollutants which is totally avoidable.
5. To make even slight improvement in the air quality of North India, more than million towers will be required, and that is unacceptable in terms of the meagre results that those towers will produce but also the amount of wasted HEPA that will be created.

What Would We Do About The Problem

We are the group of people who released India’s most affordable air purifiers, and are also the pioneers of designing the system to integrate clean air systems in the current HVAC system. The solution we have designed and implemented to integrate our air purification system in the pre-installed Air handling Units, has no impact on the AHU, but cleans the air upto WHO limit.

The best way to eliminate the disastrous level of air pollution in Delhi can only be done by arresting the particulate matters and harmful gases at the source, before they’re released in atmosphere.

The EPA like policy is highly advised for India, in which industries are responsible to have a level of purification before they release the harmful gases and particulate matter. Same goes for biomass burning and open drainage system. We need to target the sources, because once released outside, the air is difficult to contain and clean.#hvac #airpollution #buildings #airpurification #coolingsystem #sustainability #smartcities #urban #urbandesign