Intense, frequent heatwaves measurably worsening air quality: WMO

Increasingly intense and frequent heatwaves, compounded by wildfires and desert dust, is measurably worsening air quality, according to a new report by the World Meteorological Organization (WMO).

Putting heatwaves in the spotlight, the report showed that heatwaves in the US and Europe, triggering wildfires and accompanied by desert dust intrusions, respectively, both led to dangerous air quality in 2022, affecting human health and environment.

It is not just high temperatures which are a hazard, but the impacts of resulting pollution, often overlooked, are just as pernicious, the 2023 WMO Air Quality and Climate Bulletin, the third in an annual series, said.

Air quality and climate are interconnected because the chemical agents affecting both are linked. This is because the substances contributing to climate change and degrading air quality are often emitted by the same sources.

For example, fossil fuel combustion emitting carbon dioxide (CO2) and nitrogen oxide (NO) can lead to the forming of aerosols, which significantly contribute to particulate matter (PM) pollution, impacting air quality.

The summer heatwave of 2022, the hottest on record in Europe, led to enhanced PM and ground-level ozone levels.

Several European air quality monitoring sites exceeded the World Health Organization's ozone air quality guideline level of 100 ug/cum (micrograms per cubic metre) for an 8-hour exposure, the report said.

The unusually high desert dust intrusion over the Mediterranean and Europe in the latter half of August 2022, causing high PM content, coupled with high temperatures, affected human health and well-being, it said.

While ozone in the Earth's stratosphere protects people from the sun's harmful ultra-violet rays, the ozone closer to ground harms human health, in addition to lowering staple food crop yield, both in quality and quantity.

Ozone-induced wheat and soybean losses recorded were as high as 15-30 per cent in key agricultural areas of India and China, even as ozone-induced crop losses averaged at 4.4-12.4 per cent for staple food crops globally, the report said.

Heatwaves and dry conditions are also conducive to wildfires, which, once started, propagate rapidly upon encountering dry, easily combustible vegetation, further adding to aerosol emissions.

A lengthy heatwave in September 2022 correlated with anomalously high levels of biomass burning across the north-western US, leading to unhealthy air quality across much of the region, the report said quoting the US Environmental Protection Agency (EPA).

These fires were also found to majorly contribute to nitrogen deposition in several natural ecosystems, thereby impacting biodiversity and clean drinking water, along with air quality.

While the Bulletin related to 2022, what we are witnessing in 2023 is even more extreme, said WMO Secretary-General Petteri Taalas.

"July was the hottest ever month on record, with intense heat in many parts of the northern hemisphere and this continued through August," he said.

"Wildfires have roared through huge swathes of Canada, caused tragic devastation and death in Hawaii, and also inflicted major damage and casualties in the Mediterranean region. This has caused dangerous air quality levels for many millions of people, and sent plumes of smoke across the Atlantic and into the Arctic," he said.

"Climate change and air quality cannot be treated separately. They go hand-in-hand and must be tackled together to break this vicious cycle," he said.

The WMO report was released to coincide with the International Day of Clean Air for blue skies on 7 September, the theme for which this year is Together for Clean Air.