On hot summer days in London, UK I regularly walk along some of the most trafficked streets (vehicles). Whilst the pollution is not always visible, I can clearly smell the exhaust fumes of the passing busses and feel it settling on my skin. It does not surprise me reading articles with titles including, “London’s Air is as Bad as Smoking” (credited for the title of this post).

Pollution is arguably the biggest hazard to human health today, especially in our cities (although Donald Trump doesn’t agree). With this concern in my mind, I wanted to uncover some of the worst places for my health to visit.

What is PM 2.5 and PM 10?

Particle pollution, also called particulate matter (PM), is a mixture of solids and liquid droplets floating in the air. Some particles are released directly from a specific source, while others form in complicated chemical reactions in the atmosphere.

Coarse dust particles (PM 10 ) are 2.5 to 10 micrometers in diameter. Sources include crushing or grinding operations and dust stirred up by vehicles on roads. Fine particles (PM 2.5 ) are 2.5 micrometers in diameter or smaller, and can only be seen with an electron microscope. Fine particles are produced from all types of combustion, including motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, and some industrial processes. PM2.5 particles are considered most damaging to health .



Methodology

The World Health Organisation produce a Global Urban Ambient Air Pollution Database (data from 2016 update). The primary sources of data for this are official reporting from countries to WHO, official national / subnational reports and national / subnational web sites containing measurements of PM10 or PM2.5 and the relevant national agencies. The dataset covers 2972 cities from 184 countries.

Analysis

PM2.5 pollution levels by country

Interactive map.

Top 10 countries by total PM2.5 pollution level

Country PM2.5 Urban 2014 mean annual μg/m3 PM2.5 Urban rank 2014 PM2.5 Total Country 2014 mean annual μg/m3 PM2.5 Total Country Rank 2014 Saudi Arabia 127.1 1 107.7 1 Qatar 104.6 2 103.4 2 Egypt 100.6 3 92.8 3 Bangladesh 88.8 4 83.5 4 Kuwait 78.4 7 74.5 5 Cameroon 63.6 12 65.2 6 Mauritania 86.2 5 64.8 7 Nepal 74.3 8 64 8 United Arab Emirates 64.4 11 63.6 9 India 65.7 10 62.4 10

Full table.

Saudi Arabia has levels of PM2.5 pollution in urban areas almost 30% higher than the next most polluted urban areas in Qatar.

For reference, the World Health Organisation recommends 10 μg/m3 (mean annual) as a guideline safe level.

Only 19 of the 179 countries (that reported PM2.5 figures) have equal to or less than the recommended 10 μg/m3 (mean annual) level in urban areas. 20 of the 184 reported countries have total pollution less than this recommendation.

The lowest levels of pollution are found in the Soloman Islands with urban and total PM2.5 levels equal to 5μg/m3. Notably, larger countries including the United States have urban (8.4μg/m3) and total (8.2μg/m3) PM2.5 levels below 10μg/m3.

PM2.5 pollution levels by city (best and worst)

Rank Country City/Town Annual mean, ug/m3 1 Iran (Islamic Republic of) Zabol 217 2 India Gwalior 176 3 India Allahabad 170 4 Saudi Arabia Riyadh 156 5 Saudi Arabia Al Jubail 152 6 India Patna 149 7 India Raipur 144 8 Cameroon Bamenda 132 9 China Xingtai 128 10 China Baoding 126 … 2963 United States of America Not in a City,McKenzie,ND 3.20 2964 Canada AUCLAIR 3.00 2964 Canada NORMAN WELLS 3.00 2966 New Zealand Te Anau 2.73 2967 United States of America Not in a City,Custer,SD 2.40 2968 United States of America Not in a City,Converse,WY 2.30 2969 Sweden KIRUNA 2.27 2970 Finland Muonio 2.21 2971 United States of America Wenden, AZ 2.00 2972 United States of America Sinclair,Carbon,WY 1.60

Full list.

Zabol, Iran is the worst polluted city according to the World Health Organisations Air Pollution database by some margin (217 ug/m3 annual mean, 2000% above WHO safe recommended levels!).

4 of the top 10 most polluted cities are in India. 32 of all 2972 cities considered have PM2.5 pollution levels above 10μg/m3 mean annual.

At the other end of the spectrum, many of the least polluted areas are not cities, unsurprisingly. 5 of the least polluted 10 areas are all in the US and all have PM2.5 levels way below the 10μg/m3 WHO recommendation.

856 cities considered (of 1972 total) all have less than or equal to 10μg/m3 mean annual PM2.5 pollution.

Improvements

From my brief research it would appear there is some disparity in the way pollution levels are reported. Whilst this analysis provides a good overview to the problem of pollution, it could be worth comparing such analysis to the way data is reported (sensor distributions in countries, etc).

Looking at pollution as a problem, it would also be valuable to compare levels of pollution against population numbers to understand how wide the impact is.

tl;dr

Areas of the Middle East are some of the worst polluted on earth, and most dangerous to your health.

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