Stationary combustion sources: One of the main sources of air pollution is combustion plants, which are usually the largest sources of pollutants in most developed countries. These can be sources of nitrogen oxides and sulphur dioxide emissions and, in specifically coal and oil plants, volatile organic compounds are commonly emitted. Flue gas desulphurisation can reduce emissions from coal-fired power plants and electrostatic precipitators can limit particulate emissions.
Other industrial sources: These are often esoteric pollutants released as fugitive emissions from specific chemical plants, due to its nature it’s usually unquantifiable. The effects of the release of emissions are smaller, especially compared to that of stationary combustion sources and road transport.
Figure 1: The Health effects of air pollution; source: World Health Organisation
Following a period of backlash over the ineffectiveness of the 1956 Clean Air Act, the 1968 Clean Air Act was implemented as an addendum to the original. This made it illegal to emit ‘dark smoke’ from a chimney; ‘dark smoke’ was later defined as darker than shade 2 on the Ringelmann chart. This gave the government power to limit the emissions from the individual by requiring them to fit new furnaces. It also gave the government the power to tighten control on the smoke control areas, by monitoring the sale of unauthorised fuels.
To keep up with modern emissions, the 1993 Clean Air Act was employed to consolidate the last two acts and their amendments. New additions to this act are that there is a requirement that all new industrial furnaces must be ‘smokeless’. Also, chimney height regulations came into effect, where tall chimneys were ordered to be lowered to allow adequate dispersal of pollutant emissions. Moreover, further information became available to the public regarding how to comply with the new rulings and make better choices to improve air quality.
Figure 2: Changes in the concentration of London's air pollution over 50 years; source: Clean Air Act after 50 years
To combat this, the Mayor’s Office has introduced many schemes to reduce the amount of pollution in the air and increase the air quality for the rising population. For example, by introducing a congestion charge into central London, it resulted in 60,000 fewer car movements per day, equating to 30% fewer cars on the road and further reducing the congestion in London. The congestion charge acts in the way that individuals need to pay £11.50 a day to drive within the charging zone between 7 am and 6 pm on weekdays. Another way of reducing pollution in London is through the Toxicity Charge (T-charge), this is a £10 charge on older, more polluting vehicles when entering London. This is in addition to the congestion charge. And finally, to promote alternative methods of sustainable travel, the Mayor’s Office have spent £300 million on retrofitting thousands of buses with non-diesel engines and put them on the capitals most polluted routes, called Low Emission Bus Zones. These 12 Low Emission Bus Zones are expected to reduce nitrogen oxides by 84%.
Figure 3: Trends in UK sulphur dioxide, nitrogen oxides, non-methane volatile organic compounds, ammonia and particulate matter (PM10 and PM2.5) emissions 1970-2016; source House of Commons
Table 1: Comparison of the benefits of reducing PM2.5 by 10 micrograms per cubic meter, the elimination of of motor vehicle traffic accidents and the elimination of passive smoking; source: Environmental Protection UK
Following this undesirable award, Mexico adopted the Management Programme to Improve Air Quality (Proaire) in the late 1990s. This was a group of social policies that helped cut the number of cars on the road, improve the public transport system and generally limit the number of greenhouse gases and harmful pollutants from entering the atmosphere. This scheme helped drop the AQI rating of 300 in the 1980s to average just less than 150 AQI within two decades. It also reduced the amount of ozone in the atmosphere from 500 parts per billion (ppb) to 150 ppb, showing a 70% decrease in the same time.
In 2008, further clean air initiatives were developed in the form of Mexico City’s Green Plan, Plan Verde. It worked with the original Proaire scheme and adapted it to promote sustainability and further reduce emissions. It emphasises local action and reintroduced the past ideas of ‘Hoy No Circula’ (Today don’t drive) and ‘Muevete en Bici’ (Get on your bike) campaigns.
In the 1980’s, Mexico City spent the majority of the year on high alert, having particulate concentrations above the recommended amount for human health. In the past few years, a high alert has only been issued a few times a year.
Figure 4: The green house gas emissions of Mexico from 1990 to 2014; source: Climate Watch
This pollution doesn’t just come from traffic and industry, a sizable proportion of pollution from India is from intermittent sources, for example, the burning of biomass, most commonly wood, as 75% of households in India use wood as a main source of fuel. Not to mention the ‘slash and burn’ agricultural techniques that occur yearly in the paddy fields north of New Delhi, which is often blown into the capital and beyond, contributing to the vast array of pollutants that plague the city. Furthermore, even the traditional Indian burial service contributes to the poor air quality, as remains are burnt outside, further releasing pollutants, including volatile organic compounds that can be carcinogenic.
New Delhi has attempted to mitigate the effects of the huge amounts of pollution in the city, one of these schemes is the alternate day traffic system. In this scheme cars with odd and even number plates were only allowed on the roads of the city on alternate days. According to the New Delhi government, pollution fell by about a quarter in the two-week trial period, and this helped ease the congested traffic. There was also a large amount of opposition to this, about 90%, but as the two-week period came to a close the majority of those polled expressed support for the scheme. This boosted the public transport system and, due to the lack of congestion, the buses and trams could move much faster and much further than before.
Furthermore, New Delhi has instigated a Graded Response Action Plan (GRAP) that direct the local government, law enforcement and public what to do when the air quality declines to a certain level. The Delhi Pollution Control Committee can stop construction and shut down power plants. The transport department can reintroduce their odd/even scheme, increase public transport service and assign heavy fines to polluting vehicles. The DPCC have even created an app, phone number and email address for the public to lodge complaints about other individuals who are contributing to the pollution problem.
Figure 5: The change in annual concentrations of PM2.5 in different Indian cities between 2014 and 2016; source: World Health Organisation
Facing strong public pressure, China’s government implemented its Action Plan on Prevention & Control of Air Pollution in 2013. In the plan, the government pledged to slash coal consumption from around 67% of the nation’s total energy use in 2012 to 65% by 2017. Further plans aim to reduce China’s particulate matter (2.5) by 10% from 2012 to 2017, with Beijing aiming for a 25% reduction by then.
Figure 6: The concentration of PM2.5 in China in 2015 and 2040, following the predicted new policies scenario; source: World Energy Outlook 2017 - International Energy Agency