The latest data from the World Health Organization (WHO) shows that about 7 million people die each year—one in eight of total global deaths—because of exposure to polluting gases, confirming air pollution as the world’s largest single environmental health risk.
Air pollution includes greenhouse gases (GHG) –ozone, carbon dioxide (CO2), methane (CH4), nitrogen dioxide (NOX), and fluorinated gases (halocarbons)—particle matter (PM) and sulphur dioxide (SO2).
The Montreal Protocol was one of the most successful multilateral environmental agreements, paving the way for the UN climate talks. This phased out ozone-depleting chlorofluorocarbons (CFCs) through credible enforcement threat of trade restrictions, combined with side payments to developing countries.
Efforts to reduce other air pollutants have tended to be more localised. NOX and SO2 are major polluting gases produced by heavy industry and road traffic, by contributing to the formation and modification of other pollutants, such as ozone, PM, and acid rain.
Air pollution is a significant risk factor for many diseases and health conditions, including respiratory infections, heart disease, chronic obstructive pulmonary disease (COPD, including chronic bronchitis and emphysema) and asthma, strokes, and lung cancer.
PM, a complex mixture of air-borne particles and liquid droplets composed of acids (such as nitrates and sulfates), ammonium, water, elemental carbon, organic chemicals, metals, and soil material, can also significantly impact human and animal health.
The US Clean Air Act, designed to control air pollution on a national level, is the US’s first and most influential modern environmental law. In Europe, the 2008 EU Ambient Air Quality Directive sets legally binding limits for major air pollutants.
China issued its first pollution ‘red alert’ in 2015, with strict limits placed on car use, and factory shutdowns in Beijing. Then, in 2016, its 13th Five-Year Plan included targets to improve environmental standards across the board, focusing particularly on measures to tackle urban smog.
China has been focusing on the development of alternative energy sources such as nuclear, hydro and compressed natural gas. The latest plan entails closing outdated capacity of iron, steel, aluminium and cement and increasing nuclear capacity and other renewable sources.
Globally, the burning of coal to produce power, and secondly to power steel plants—mainly in China and India—is the single biggest contributor to GHGs and air pollution. Steel manufacturing also produces dangerous PM pollution containing minerals, metals, and polluting gases such as NOX and SO2.
Rising levels of dangerous gases from industrial processes has led to the development of a diverse range of air pollution control devices, which remove particulate and gases from industrial emissions. These either use liquid to wash unwanted pollutants from emissions or inject a compound that causes a chemical reaction to “wash out” acid gases.
Worsening air quality has led some governments and city mayors to clamp down on diesel-powered cars and trucks, which produce NOX and tiny particulates that can lodge in the lungs.
The need to clean up traffic pollution is leading many vehicle manufacturers to develop fuel-efficient, low-emission engines, as well as hybrid and electric vehicles. Some examples of emission control devices used for diesel retrofit include diesel oxidation catalysts, diesel particulate filters, NOX catalysts, selective catalytic reduction, and exhaust gas recirculation.
Shipping comes a close second to road transport as a major contributor to global air pollution, accounting for 18 to 30 percent of NOX and 9 percent of SO2. With China the world’s busiest shipping nation (over 60 percent of the world’s seaborne cargoes and 30% of the world’s shipping containers pass through the country’s ports), the government started phasing in regulations forcing ships to use 80 percent less sulphur than standard marine fuels. The London-based International Maritime Organisation (IMO), which regulates world shipping, is set to introduce rules in the coming years to replace dirty bunker fuels with low sulphur fuel.