WHO’s urban ambient air pollution data shows US outdoor air quality has improved in recent years at the same time the rest of the world’s outdoor air pollution has increased 8%, because the Obama Administration’s Clean Power Plan and other initiatives are forcing coal plants to close, being replaced by plentiful gas unlocked during the shale gas revolution.

While transport is also a key generator of particulate matter, older diesel and petroleum engines are losing market share to electric vehicles, and in the baseload generation space that often powers electric vehicles, gas fired electricity generation increase by 50% in the US since 2008, securing one third of the energy mix.

The US Energy Information Administration expects to see more electricity generation from renewables – especially solar and wind – and gas over the next 25 years compared with projections without the CPP, which the Republicans are trying to dismantle.

The EIA expects coal to continue to lose ground, while generation from other fuels such as nuclear or hydroelectricity are expected to remain relatively unchanged.

With the CPP, the EIA expects that CO2 emissions will be lower, however retail electricity prices will be higher.

WHO examined some 3000 cities around the globe, finding that an alarming 80% of people in urban areas that monitor air pollution worldwide are exposed to PM (particulate matter) 2.5 concentration levels that exceed WHO standards, compared to just 20% in the US.

The US Environmental Protection Agency says that PM2.5 can cause “early death, cardiovascular or respiratory harm,” and WHO estimates it causes three million deaths a year.

Electrical generation from coal-fired power plants has traditionally been a primary source of PM2.5 pollution, due to the fact that nitrogen oxide and sulphur oxide can combine with water vapour to form PM 2.5.

Natural gas emits one-third the NOX, just 1% of the SOX of coal and around half of the CO2 of coal.

Natural gas also overtook coal as the leading source of US electricity generation for the first time in April 2015 and was the top electrical generation fuel in each of the last six months of 2015.

The Energy Information Agency forecasts that natural gas will top coal as the major fuel source for electricity generation this year.

The US Federal Energy Regulatory Commission’s energy says nearly 4300 megawatts of new gas-fired generation came online the first five months of this year, more than twice that of 2015.

According to EIA, switching fuels from coal to natural gas accounted for 68% of the 12% total reduction in energy-related CO2 emissions during last decade.

Those reductions have also occurred at the same time the economy grew 15%, and thanks to natural gas’ prominent role in electrical generation, energy production no longer the top industrial source of CO2 emissions, while gas process have fallen up to 40%.

The WHO data, however, has not examined the impact of volatile organic compounds such as air toxins and ozone precursors, and greenhouse gases, which have been shown to be associated with gas wells, particularly those in shale plays.

A recent study into the Bakken Shale is being used by the Colorado Department of Public Health and Environment plans to use the data to conduct a human health risk assessment.

A recent small study in Wyoming found that toxic air emissions from gas operations appear to be found in participants’ bodies at concentrations far exceeding background averages in the US population.

Scientific research indicates that in some cases VOCs might interact in ways that increase health risks in humans.

The changes in the US echo changes around the world, with BP recently reporting that coal consumption globally fell last year for the first time since 1998.

It was the largest fall on record for coal, largely as countries like China moved away from the polluting fuel, in favour of renewable power.

BP said China slowed its emissions growth and leapfrogged both Germany and the US to rank first in solar power production in 2015.

World consumption of natural gas grew 1.9% in 2015. Renewable energy in power generation also continued to rise, reaching 2.8% of global energy consumption.