What Is It That We All Call Pollution?

Air pollution is becoming more and more present in the news, in casual conversations, in the promotion of products and in many more instances. However, are we all talking about the same thing? What exactly is it that we all call ‘air pollution’?

Air pollution is a mix of natural and man-made substances in the air we breathe which is harmful to our health, it can be any physical, chemical or biological agent that modifies the natural atmosphere. Most sources of air pollution are man-made from mobile sources such as fuel powered motor vehicles; and stationary sources such as factories, refineries, power plants and forest fires. There are also other indoor sources such as building materials and cleaning products. Air pollution, as we now know is present both outdoor and indoor.

Outdoor air pollution:
  • Fine particles (burning of fossil fuels in energy production, coal and petroleum used in vehicles)
  • Gases (sulphur dioxide, nitrogen oxide, carbon monoxide, chemical vapours and others)
  • Ground-level ozone (smog)
Indoor air pollution:

Gases emanating from:

  • Household products and chemicals, or
  • Building materials such as paint, wood, furniture (asbestos, formaldehyde, lead etc)
  • Allergens such as coackroaches, mold, pollen

The World Health Organization (WHO) in 2005 issued the ‘WHO Air Quality Guidelines’ to offer guidance and limits for the most worrying air pollutants because of their threat to human health, their widespread presence in urban areas and their relevance as precursors for other toxic components: particulate matter (PM10, PM2.5), ozone (O3), nitrogen dioxide (NO2) and sulphur dioxide (SO2).

Particulate Matter

Is a mix of solid and liquid (organic or inorganic) particles suspended in the air. It is the pollutant that affects most people and is generally composed by sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water.

Ozone (O3)

Ground-level Ozone is a major component of smog, formed by the reaction of sunlight with nitrogen oxides (NOX) and volatile organic compounds (VOCs).

Nitrogen Dioxide (NO2)

NO2 is mostly the result of emissions during the combustion process (power generation, heating and engines). It is in fact, a source of nitrate aerosols that form PM2.5.

Sulphur Dioxide (SO2)

SO2 is produced from fossil fuel burning for domestic use, power generation or motor vehicles

Other components generally referred to when talking about air pollution are carbon monoxide (CO), carbon dioxide (CO2) and volatile organic compounds (VOCs), which has greater relevance when talking about indoor air pollution, although also present outdoors.

VOCs are a collection of toxic gases from solids or liquids, that are found in higher concentrations indoors (up to ten times higher). Thousands of products used indoors as construction materials, paints, varnishes, cleaning agents, activities like cooking and many more, are the source of VOCs while being used and while stored. (6) Safe levels / guidelines for exposure to VOCs are not known,, but common sense rules are that they should be kept at low levels to avoid or reduce their negative health effects, which have been well documented.

CO and CO2 are not considered as VOCs. They are both odorless, tasteless and harmful to human health but have clear differences – CO2 occurs naturally in the atmosphere and we can tolerate it in small amounts, whereas CO can cause problems even in low concentrations and is flammable.

  • PM5
    10 μg/m3 annual mean
    25 μg/m3 24-hour mean
  • PM10
    20 μg/m3 annual mean
    50 μg/m3 24-hour mean
  • NO2
    40 μg/m3 annual mean
    200 μg/m3 1-hour mean
  • SO2
    20 μg/m3 24-hour mean
    500 μg/m3 10-minute mean
  • O3 
    100 μg/m3 8-hour mean
    WHO issued these guidelines as a global standard for environmental quality. Each country can adopt the guideline at its maximum standard or take interim standards that better reflect their national balance between health risks, economic decisions, technological capacities and other political and social factors.


NIH – Air Pollution and Your Health
EPA – Pollutants and Sources
WHO – Air Pollution
WHO – WHO Challenges World to Improve Air Quality
WHO – WHO Guideline for Particulate Matter, Sulphur, Ozone…
EPA – Volatile Organic Compounds’ Impact on Indoor Air Quality

Am I Exposed to Air Pollution?

But how is our exposure to air pollution measured?

The WHO model was developed together with the University of Bath, United Kingdom and is based on data from more than 3,000 locations with ground station monitors which represent about 40% of the world’s urban population. It also includes satellite measurements and air transport models to give an annual average exposure to particulate matter (PM2.5), which are the tiny particles that penetrate deep into the body and create the greatest harm.

Another source of air quality information that is commonly used across the world is the AirNow or AQICN Apps, Facebook and webpage. This information comes from the Environmental Protection Agencies of 600 major cities in 70 countries. The information from 9,000 stations is collected and reported on an hourly basis in real time. The readings are displayed in the EPA AQI standard index and only uses PM2.5 and PM10 readings.

Is this data accurate to assess my personal exposure?

Research has shown that population exposure from fixed-site monitors do not show a clear picture of daily exposure at the individual level. In fact when comparing personal exposure measurements and ambient monitoring, there are significant differences and some studies have shown that the major variance comes from accounting for air quality during commuting to and from work, school or play. A recent study by the Massachussetts Institute of Technology (MIT) suggests that data collected through mobile phone usage to determine ‘activity patterns’ (areas most transited by people) can be linked to the traditional static air quality monitoring to give a more precise measurement of exposure to air pollution.However, this will also depend on the number of air monitoring stations in the city where you live and how close they are to your area of commute or to the area where you work, how long you spend indoors and the quality of air indoors. All in all, the current system of air quality monitors provides useful information for policy matter and to have an indication of the general air quality, but it fails to provide any given individual with an accurate account of his own personal exposure to air pollution.

There is no doubt that the most useful measure of your personal exposure is a portable air quality monitor, that can give you personalised, real-time, accurate information of your own daily exposure accounting for the quality of the air indoors as well as the outdoor air you are exposed to in your daily routine.

Taking care of your health starts by owning the data of those environmental threats that can negatively affect your health.
This is why we at meo believe that we can make a difference in your life. 

In the meantime, get informed:

  • To know the annual PM2.5 levels in the city where you live visit: www.breathelife2030.org
  • To know hourly air quality values on US EPA AQI standard visit: www.aqicn.org or download the App
  • Look for local options to access data that better represents your personal exposure.

MIT News – Measuring exposure to pollution
WHO – WHO releases country estimates on air pollution exposure and health impact
AQICN – World-wide Air Quality Monitoring Data Coverage