Exposure to certain air pollutants may increase emergency department (ED) visits for respiratory and cardiovascular diseases, a study has found.

The study, published in the journal Environment International, found that exposure to pollutants such as ground-level ozone and nitrogen oxides, which are created from burning fossil fuels, led to increased ED visits.

"We found that primary pollutants -- those that are emitted directly from a source, such as car exhaust -- were associated with ED visits for cardiovascular and respiratory diseases," said Jenna Krall from George Mason University in the US.

"Additionally, secondary pollutants -- those that are formed through chemical reactions in the air -- were linked to ED visits for respiratory diseases," Krall said.

While most past studies were conducted on a single-city level, this study looked at pollution across five cities -- Atlanta, Birmingham, Dallas, Pittsburgh, and St Louis.

The researchers analysed the associations between cardiorespiratory ED visits and twelve major air pollutants to examine short-term changes in health as pollution varies on a daily basis.

"By looking at the five cities, we hope to get a better sense of how these associations hold in general, instead of for individual cities," Krall noted.

This is also one of first multi-city studies to look at multiple air pollutants, including gases and particles, and multiple causes of ED visits, such as asthma and stroke.

It is a larger and more comprehensive study than previous work that has commonly looked at one pollutant and multiple health outcomes, or multiple pollutants and one health outcome.

"Down the line, this research has implications for how we think about future pollution regulations because the way we regulate pollutants might differ between primary and secondary pollution," said Krall.