Even though levels of PM2.5 are lower in the USA than national ambient air quality standards, pollution is still costing thousands of lives, a study has suggested.
The study was published in the journal PLOS Medicine and analysed publicly available data to directly estimate the number of deaths, by age group and sex, and loss of life expectancy due to current PM2.5 levels across the USA, as well as the benefits of reductions since 1999.
The aim of the study was to quantify the current mortality burden of PM2.5 pollution and lives saved as a result of recent PM2.5 reductions.
It found that in 2015, concentrations of PM2.5 were below the USA’s ambient air quality standard of 12 µg/m3 in every county in the country except four.
They compared this data with 1999, where 59% of every county in the country reported levels higher than this standard, with Fresno County in California having levels of 22.1 ug/m3.
However, even though these reductions in PM2.5 since 1999 have lowered mortality in the great majority of counties, researchers found that PM2.5 pollution in excess of the lowest observed concentration (2.8 ?g/m3) was responsible for an estimated 30,000 deaths.
The life expectancy loss due to PM2.5 was largest around Los Angeles and in some southern states, such as Arkansas, Oklahoma and Alabama.
Nationally, population-weighted PM2.5 concentrations in the USA declined from 13.6 µg/m3 in 1999 to 8.0 µg/m3 in 2015.
The researchers say these reductions have benefitted ‘virtually the entire country’, adding between 0.12 and 0.17 years to the national life expectancy, despite the 30,000 lives lost.
Professor Majid Ezzati, lead author of the research from Imperial’s School of Public Health said: ‘We’ve known for some time that these particles can be deadly. This study suggests even at seemingly low concentrations – mostly below current limits – they still cause tens of thousands of deaths.
‘Lowering the PM2.5 standard below the current level is likely to improve the health of the US nation, and reduce health inequality.’
He added: ‘US PM2.5 concentrations are generally lower than those in many Europe cities –– which suggests there may also be substantial number of deaths in Europe associated with air pollution.’
The report was written by an international team of researchers from the Center for Air, Climate, and Energy Solutions led by Majid Ezzati of Imperial College London, UK.
Last week, UK Environment Secretary Michael Gove said the upcoming Environment Bill will enshrine World Health Organisation (WHO) limits for PM2.5 in UK law.
Currently, the WHO says a safer annual mean limit for PM2.5 is 10 ?g/m3, whereas the EU recommends a level of more than double at 25?g/m3.
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