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Indoor Air Quality : Introduction and probable Solutions

Anurag Bajpai

Co-founder: GreenTree Global | Building GT Academy

发布日期: 2017年11月24日

Impact of air pollution

As per a 2017 report by World Health Organisation (WHO), environmental pollution can be held responsible for more than 1 in 4 deaths in children under the age of five years.This is something each of us should be thinking about very seriously. Talking specifically about air pollution, the WHO report mentions that every year 570 000 children under 5 years die from respiratory infections, such as pneumonia, attributable to indoor and outdoor air pollution, and secondhand smoke.

Air quality is of particular concern to those of us living and working in the Delhi NCR region. Every winter brings with it many many days of particularly toxic smog. This is especially worrying since even a casual short term exposure to air pollution results in aggravated respiratory and cardiovascular stress and illness. Long term exposure can have permanent health effects like

Accelerated aging of the lungs
Loss of lung capacity and decreased lung function
Development of diseases such as asthma, bronchitis, emphysema, and possibly cancer
Shortened life span

Apart from the typically vulnerable sections like the elderly, children and pregnant women, air pollution also particularly affects

Those with pre-existing heart and respiratory conditions like asthma, coronary heart disease etc
All outdoor workers
Athlete who exercise vigorously outdoors

What is Air Quality?

Air quality is a measure of the level of air pollution. This can be measured via either passive or active sampling methods. Essentially a sample of polluted air is analysed for various pollutants like nitrogen oxides, sulphur oxides, benzene, carbon monoxide and particulates. The concentration of pollutants by volume is then aggregated and typically expressed in parts per million by volume.

The particulate matter (PM) pollution is measured in terms of concentrations of particulates falling in different size ranges. Generally two variations of these are used

PM10 : inhalable particles, with diameters that are generally 10 micrometers and smaller; and
PM2.5 : fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller.

For reference, the average human hair is about 70 micrometer thick, which makes it roughly 30 times a PM2.5 particle.

There are two standard ways of measuring air quality

Air Quality Index (AQI)

This tells us about the level of pollution in the outdoor air. AQI is measured into six range categories. A more in depth interpretation may be found here (https://en.wikipedia.org/wiki/Air_quality_index) with India specific info here (https://en.wikipedia.org/wiki/Air_quality_index#India) (maybe embed the image here directly)

As a side note, the AQI for Delhi ranged between 500 to 900 for days between 7 nov to 14 nov 2017 (as per https://cpcb.nic.in/ at the time of writing the article).

Indoor Air Quality (IAQ)

IAQ does not have a specific measure of its own as of now. The standards are still being considered by the Indoor Air Quality Organisation (https://www.iaqa.org). When talking about IAQ, not only do we need to consider the average AIQ at the location but also some common pollutants that are of even more concern in an indoor environment. A major source of indoor air pollution in the developing countries is burning of biomass like wood, charcoal, animal dung etc for cooking and heating purposes.

Some of the common pollutants that affect the indoor air quality are second hand smoke, radon (a radioactive gas found in the soil of many areas), carbon monoxide, molds and other allergen, asbestos fibers, volatile organic compounds (VOCs), other microbes, carbon dioxide, ozone and particulate matters.

Mitigating Approaches

Air pollution is certainly a matter of concern whether it is outdoors or indoors. However mitigating the outside air pollution is not entirely in the hands of an individual. So without any intention of minimising the need to improve the outdoor air quality, we’ll be focusing on approaches that can be taken to improve the indoor air quality.

Homes and apartments

Homes in india can be divided into two main categories from the point of view of indoor air quality. First we have the typical traditional homes which are essentially open to the environment, both in terms of ventilation and temperature control. Second we have homes whose design allows sealing of most of the home areas for the purposes of cooling via air conditioners. There are some actions which you can take to improve the indoor air quality of your home irrespective of the category it falls under.

Cooking and indoor heating

This is one of the biggest sources of indoor pollution. Make sure that the fuel you use (if any) is as clean burning as possible and that there is minimal possibility of carbon monoxide concentrations building up. This caution also applies to homes that use gas heaters. There are currently many initiatives from the government and NGOs relating to clean burning stoves for rural and low income households.

Also having an exhaust chimney is a great help in reducing any harmful effects.

Washrooms and basements

Spaces that tend to get damp like washrooms, basements etc are more prone to mold and other microbial growth. This should be discouraged by using appropriate coatings and flooring options. Most importantly, there should be a good level of ventilation and air circulation to promote quick drying and reduce general humidity. Thus having the right exhaust system in these places is quite important.

Other sources

Do not smoke inside a closed area. The smoke and the harmful chemicals take a lot longer to dissipate in an indoor area as compared to outside.
If the climate allows, avoid having rugs and carpets. They collect mites, dust, dander and allergens, thus reducing the quality of air and increasing allergy cases.
Keep surfaces clean and avoid having a lot of stuff pile up over time.

Sealable spaces

In the last decade or so, homes and apartments have started featuring windows and doors that seal well to make the spaces easier to cool via air conditioners. Though this arrangement provides a good degree of thermal comfort in the hot summer months, there are a few points of concern as well from the air quality perspective.

The good news is that such spaces are less affected in times when the AQI outside is very high. So they are in general better than outside. However, over 99% of the ACs in use in homes in India, do not have any provision for fresh air intake. Correspondingly the air inside the home keeps getting cooled and recirculated. This does nothing to remove the accumulating carbon dioxide in the air, not to mention other indoor pollutants like VOCs etc.

The solution is for this is to make sure that outside air is allowed to circulate in the rooms at least once a day and any time it feels a bit stuffy. A stuffy feeling could be due to higher than safe levels of carbon dioxide and other pollutants in the room’s air. Early morning can be a good time to open the doors and windows since typically outside pollution is low at this time.

Indoor plants

Lately many articles in news and on the internet claim that certain indoor plants are good in removing certain indoor pollutants. The NASA Clean Air study (provide wiki link) did show that certain common plants are good at removing certain toxic pollutants from indoor air like benzene, formaldehyde and trichloroethylene. The NASA researchers suggest at least one healthy plant every 100 square feet of indoor space for noticeable effect. The list here provides further information about the plants and which pollutants they are effective for.

Buildings requiring HVAC systems

Buildings like commercial complexes, hospitals, hotels etc typically need HVAC systems to maintain thermal comfort. Maintaining a good level of air quality requires that the HVAC system also be integrated with good air filtration systems. Typically these filters are HEPA compliant.

HEPA (High Efficiency Particulate Arrestance) filtration

The HEPA standard, first set forth in 1983 in the US, mandates that a HEPA compliant filter must capture at least 99.97 percent of particles larger than 0.3 μm (micrometers, or microns) in size, while only impeding the flow of air by a relatively small amount.

The filters are typically made from a fabric which aims to have lots of tangled and warped threads. As air passes through the filter, the particles get trapped in the filter. There are a few additional factors that are of concern (depending on the requirements) when choosing a filter.

Airflow - The volume of air that passes through the filter per second.
Temperature - The temperature range of air/gas stream the filter is rated to be effective and safe for.
Pollutant Loading - This is related to the dust/pollutant holding capacity of the filter. Thus it depends on the rate of gain of weight of the filter as compared with the loss in its ability to process a volume of air (airflow)
Other considerations - Examples of other considerations could be high moisture or corrosive content in the air being filtered. Concerns like in the case of nuclear reactors where radioactive particles are the issue or in hospital units where microbes could be the issue are also covered under this.

Conclusion:

In conclusion, improving the air quality inside and outside the spaces we live and work in is both important and urgent. The Delhi government has focused on reducing air pollution by monitoring and reducing the pollution caused due to private transport. Correspondingly a mass transit system (metro) has been built and is continually being expanded on. Other urban initiatives like increasing a city’s green cover, regulating polluting industries like thermal power plants etc also need to be followed up. China can be a big inspiration in this area since they’ve managed to get huge results in the area of managing pollution across the country.

Over time, better alternatives to certain common problems will also become generally available due to advances in science, technology and manufacturing industry. Electric vehicles for example are on the cusp of changing the pollution due to transport narrative.

Yet in the meantime we should not remain complacent. The simple steps like including indoor plants, upgrading the means of cooking and heating etc should be undertaken by everyone on a priority basis. Additionally the air quality should be periodically checked and monitored. In case of any deterioration, the root cause must be found out and an appropriate solution implemented. All is certainly not lost yet.