Our air is mainly polluted by:
Nitrogen Dioxide (NO2) which comes mainly from vehicles and gas heating.
Ozone, created by pollution in the atmosphere
Particulate matter – mixtures of solid particles and liquid droplets in the air. This includes soot emitted from car exhausts, bits falling off car tyres and gas central heating boiler emissions.
According to this explainer, particulate matter varies in size (i.e. the diameter or width of the particle). PM2.5 refers to the mass per cubic metre of air of particles with a size (diameter) generally less than 2.5 micrometres (µm). PM2.5 is also known as fine particulate matter (2.5 micrometres is one 400th of a millimetre). PM10 is, or course, larger.
No amount of pollution is good. More than 5% of deaths of people over 30 are due to it. The World Health Organisation (WHO) and the government set limits
The WHO PM2.5 limit is that no person should absorb more than 5 micrograms per cubic metre of air breathed in during a year. The WHO limits are explained here. The UK government has approved 10 micrograms over a year, a higher level of pollution than the WHO.
You can sign up if you want to receive a pollution forecast every day here:
https://email.londonair.org.uk/h/j/C181D943EF3ED945
Or if you only want alerted before Moderate or High days you can sign up for this one.
https://email.londonair.org.uk/h/j/9A21AF316994EE6D
We have installed a pollution monitor to help contribute data from our area
on a lamp post on the Broadwater Farm Estate:
More photos here. Data collected is available on our data pages
Our sensor measures PM2.5 and NO2. The amount of PM2.5 is measured as the amount of light the pollution scatters – the number and size of particulates in the air change how much light gets through.
To measure NO2, the sensor measures the amount of current coming from an electrolyte inside it. The amount of electrical current NO2 causes the electrolyte to produce is a measure of NO2 concentration. The table below shows numbers for common pollutants:
The averaging periods and concentration breakpoints for each pollutant in the index are:
Air pollution can be caused by people and by nature. People are leading contributors to city air pollution. Mainly from combustion – fossil-fuel-powered planes, trains, and automobiles and industry (power stations, refineries, and factories), biomass (burning plant matter or coal for heating, cooking, and energy), and agriculture. Natural sources include smoke, windblown or kicked-up dust, dirt and sand.
Sources can be categorised thus:
Transport
Most motor vehicles, trains, planes, and ships emit high levels of fine particulate matter (PM2.5), ozone, and nitrogen dioxide (NO2).
There is a strong correlation between per capita transport emissions and income. As standards of living and economic activity increase, so too does the demand for transport.
Household
The building and construction of homes and furnishings. Cooking and heating with coal or wood burning.
Industry
Pollution from factories, mines, and oil refineries. Coal power plants and boilers for heat and power generation.
Industry produces nitrogen oxides (NOx), hydrogen sulfide, volatile organic compounds (VOCs), and particulate matter (PM), contributing to ozone and smog.
Agriculture
Fertilisers used on agricultural land creates fine-particulate air pollution. A study in Geophysical Research Letters showed that farm-originated pollution was greater than all other people-made sources of PM in much of the United States, Europe, Russia, and China.
Use of land for farming is on the rise around the world as the demand for animal products and per capita food increase.
Natural sources
The impact of volcanic activity, wildfires, dust or sandstorms on air quality is dependent on location. We’re lucky we don’t have these issues.
Here is one person’s explanation of why we should all take an interest