Heatwaves and air pollution can be a deadly combination, study finds
The researchers found that the death toll rose on both hot days and days with high levels of fine particle air pollution, known as PM2.5. But on days when an area is hit by both high heat and high air pollution, the impact is much higher than it would be alone. On these days of ultra-high temperature and pollution, the risk of death was about three times greater than the effects of high heat or high air pollution alone.
The more extreme the temperature and pollution, the higher the risk. In the top 10% of the hottest and most polluted days, there was a 4% increased risk of death compared with days without extreme conditions. In the first 1% of days, the risk of death increased by 21%; and among those over 75, the risk of death increased by more than one-third on these days.
Scientists at the University of Southern California found that on the hottest days, the excess mortality risk from high heat and extreme levels of PM2.5 air pollution was about three times higher than either alone. Exposure to extreme heat and particulate air pollution can harm human health in several ways.
Oxidative stress is the most common biological pathway associated with particulate air pollution and heat exposure. Oxidative stress is an imbalance between the production of highly reactive molecules called reactive oxygen species (ROS) and the body’s ability to clear them. It is associated with lung disease as well as other diseases. Antioxidants help clean up these molecules, but particulate air pollution and high temperatures disrupt this balance by excessive metabolic ROS production and reduced antioxidant activity.
The study also showed that the effects of particulate air pollution and extreme heat were greater when nighttime heat and pollution occurred at the same time. High nighttime temperatures can interfere with normal sleep and can lead to chronic health conditions, such as heart disease and obesity, and disrupt the way the body regulates temperature. Older adults may be more vulnerable to extreme heat and air pollution exposure, in part because such stress is created on top of chronic age-related health conditions such as heart disease, high blood pressure, diabetes or chronic lung disease.
Impaired thermoregulation in response to heat may also occur with age. Also, older adults may have limited mobility and therefore be less able to go to refrigeration centers or medical facilities and less able to afford themair conditioner。