Higher pollution levels are linked to an increased number of strokes, according to a new study that reaffirms the growing evidence that climate change and overall air quality contributes to cardiovascular disease.

The research, which used data from the US and China, is one of the first to study the interaction between air quality and the number of stroke cases along with the potential effect of temperatures on the association.

Researchers used data from the two countries because they "are the world's two largest emitters of greenhouse gases and responsible for about one-third of global warming to date," said lead study author Longjian Liu, an associate professor at Drexel University in the US.

The team evaluated air quality data collected between 2010 and 2013 from 1,118 counties in 49 states in the US and from 120 cities in 32 provinces in China.

Particulate matter (PM) is the term for particles found in the air, including dust, dirt, smoke and liquid droplets.

Particles less than 2.5 micrometres in diameter (PM2.5) pose the greatest health risks due to their small size. They are created from combustion from cars, power plants, forest fires and others.

Across the two countries, researchers found that the total number of stroke cases rose 1.19 per cent for each 10 microgrammes per cubic metre of air increase of PM2.5.

In addition, researchers found a significant regional variation in PM2.5 levels that was linked to the number of stroke cases.

Overall, the southern region of US had the highest average annual PM2.5 while the West had the lowest - which correlates with the fact that people living in the South had the highest prevalence of stroke at 4.2 per cent compared with those in the West who had the lowest at 3 per cent, Liu said.

Researchers also found that temperature had an impact on air quality and risk of stroke.

"Seasonal variations in air quality can be partly attributable to the climate changes,"  Liu said.

"In the summer, there are lots of rainy and windy days, which can help disperse air pollution. High temperatures create a critical thermal stress that may lead to an increased risk for stroke and other heat- and air quality-related illnesses and deaths," he said.

Moreover, "patients with stroke are in danger of dehydration due to high temperatures in the summer, and are in danger of suffering from pneumonia, influenza and other respiratory diseases in winter," Liu said.

"Women and the elderly also appear more vulnerable to stroke risk due to air quality and heat-related diseases," he said.