There is an "excessive heat watch" for later in the week and there is a high heat prediction.

A new heat wave is endangering public health and raising the likelihood of wildfires. In addition to these hot days and nights, hazardous amounts of pollution have been detected in air quality data. Sounds recognizable? In many parts of the world, this situation is becoming more and more the new standard.

In particular, for vulnerable populations like older folks, extreme heat and air pollution are harmful to human health. What transpires, though, if they both strike at once?

In order to determine this, we looked at more than 1.5 million deaths from 2014 to 2020 that were documented in California, a state vulnerable to summer heat waves and air pollution from wildfires.

Both hot days and days with high levels of the tiny particulate matter known as PM2.5 air pollution saw an increase in the number of fatalities. But the impacts were significantly more severe than they would have been for either condition alone on days when a region was affected by both high heat and high air pollution.

The risk increases with excessive pollution levels and warmth.

In comparison to days without extremes, the risk of death rose by 4% on the top 10% of warmest and most polluted days. It jumped by 21% in the top 1%, and on such days, the chance of mortality rose by more than a third in older persons over the age of 75.

The combined effects of exposure to intense heat and particle air pollution can be harmful to people's health in a number of ways. The most frequent biological relationship between heat exposure and particle air pollution is oxidative stress. Reactive oxygen species, or ROS, are highly reactive molecules that are produced in excess compared to the body's capacity to expel them, which is what is meant by oxidative stress. Among other disorders, it has been associated with pulmonary problems.

Antioxidants aid in the removal of these molecules from the environment, but heat and particle air pollution disturb this equilibrium by increasing metabolic ROS generation and decreasing antioxidant activity.

Research has also shown that when both high nighttime temperatures and pollution occur, the impacts of particle air pollution and heat extremes are magnified.