We keep reading and hearing that air pollution is high or air quality is bad and often the focus is on Dhaka and pictures of dusty roads and smog.
So what defines good or bad air quality, indoors & outdoors?
What we normally “see” as air pollution is when things have become really bad! Seriously speaking, visible air pollution or smog is when concentrations of pollution are incredibly high; most of the time even when we see “clean” air, it may not actually be clean. In fact in Dhaka, most of time even when the air is looking visibly clean there may be enough pollutants to rate the air quality as unhealthy or even hazardous.
This post tries to provide a simple overview of the major elements that result in bad air quality.
PM10 & PM2.5
We can inhale particles that are smaller than 10 microns (PM10) and PM2.5 particles at 2.5 microns or lower are even smaller. To give this a size context, human hair is 50-70 microns thick so PM2.5 particles are more than 20 times smaller than human air.
You don’t see this pollution but we breathe it in all the time.
PM 2.5 levels for air quality are defined as follows:
| < 12 ug/m3 | Good |
| 12.1 – 35.4 | Moderate |
| 35.5 – 55.4 | Unhealthy for sensitive groups |
| 55.5 – 150.4 | Unhealthy |
| 150.5 – 250.4 | Very Unhealthy |
| 250.5 – 500.4 | Hazardous |
In Dhaka we reach the following levels of PM2.5 pollution:
| Hazardous levels | 3 months of the year |
| Very Unhealthy | 2 months of the year |
| Unhealthy | 3 months of the year |
| Unhealthy for Sensitive Groups | 4 months of the year |
To restate the above, there is not even 1 month in the year where we stay at Moderate levels of pollution for the whole month, let alone Good!
Indoor Air Quality
When it comes to indoor air, apart from PM2.5 there are a number of other pollutants that impact our health.
Formaldehyde
We normally think of formaldehyde in the context of food, but formaldehyde is commonly present in our environment and homes. In small concentrations it is not harmful but in air conditioned spaced without ventilation, formaldehyde can reach harmful levels. Sources of formaldehyde in homes are:
-
-
-
- Some manufactured wood products such as cabinets, furniture, plywood, particleboard, and laminate flooring
- Permanent press fabrics (like those used for curtains and drapes or on furniture)
- Household products such as glues, paints, pesticides, cosmetics, and detergents
- Smoking
-
-
Volatile Organic Compounds (VOCs)
VOCs are gases emitted by a lot of products such as aerosol sprays, cleansers and disinfectants, moth repellents and air fresheners, paints, wood preservatives, dry-cleaned clothing, office equipment such as copiers and printers and more.
Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors.
CO2
High levels of Carbon dioxide is a common, or even prevalent, problem in offices where there is inadequate ventilation e.g. air conditioned offices without a proper ventilation system. In homes, CO2 levels rise from cooking or open flames & smoking.
Carbon Monoxide
This is primarily generated from burning substances so kitchens are typically the location where Carbon Monoxide levels can be high if there isn’t adequate ventilation.
Good Indoor Air Quality
Apart from addressing the above elements, a very important and essential requirement for good indoor air quality is sufficient ventilation or fresh air.
The standards for good indoor air quality require that indoor air is refreshed with clean fresh air at the following intervals as a minimum:
| Residences | Every 3 hours |
| Offices & Shops | Every 30 minutes |
| Gyms | Every 15 minutes |
| Schools | Every 12 minutes |
| Restaurants | Every 10 minutes |
Outdoor Air Quality
Outdoor air pollutants are largely PM2.5, PM10, Ozone (O3), Nitrogen dioxide (NO2) & Sulphur dioxide (SO2).
The main sources of these pollutants are industrial, construction and fossil fuels.
According to WHO, in 2016 there were 4.2 million pollution related premature deaths worldwide of which 91% occurred in low- and middle-income countries.
