The double impact of extreme heat, ozone disproportionately harms poorer areas



Scientists at UC San Diego, San Diego State University, and colleagues find that extreme heat and high levels of ozone, often present together during California summers, affect some zip codes more than others.

The most affected areas of the state are generally the poorest, with higher numbers of unemployed and higher car traffic. The scientific team based the finding on data regarding the high number of people sent to hospital for lung distress and respiratory infections in low-income postal codes.

The study identified hot spots throughout the Central Valley, areas of San Diego County east of downtown San Diego, and places like San Bernardino, where Los Angeles Basin smog is often trapped. by the surrounding mountain ranges, among others.

The results appear the week of May 24 in the newspaper Proceedings of the National Academy of Sciences. The Office of Environmental Health Hazard Assessment, a division of the California Environmental Protection Agency, funded the research.

“This information can be used to activate measures to protect populations in areas that we know will be at increased risk of suffering a health burden from these concurrent environmental events and to maximize public health benefits.” said lead study author Lara Schwarz, graduate. student in a joint doctoral program at San Diego State and the Herbert Wertheim School of Public Health and Human Longevity Science at UC San Diego.

In places like California, these public health risks are expected to appear more frequently in unison as the climate continues to warm and heat waves become more frequent and lasting. The study could allow for more focused public health efforts due to its unprecedented consideration of two common hazards in tandem and its relatively high-resolution distribution of where they are most likely to cause problems. Previous studies had tended to assess health trends only at the city or regional level.

“Understanding the health effects of worsening environmental events such as extreme heat and various air pollutants like ground-level ozone becomes a priority in a changing climate,” said study co-author Tarik Benmarhnia, Climate change epidemiologist with appointments at the Scripps Institution at UC San Diego. Oceanography and Herbert Wertheim School of Public Health and Human Longevity Science. “Such events are more frequent, intense and tend to occur simultaneously, potentially creating synergistic effects on the health of the population and having an impact on the most vulnerable communities.”

The work could inform early warning systems and prioritize resources more effectively than at present, the researchers said.

Ozone, a gas and a molecular form variant of oxygen, is formed in the lower atmosphere by the reaction of various hydrocarbons in sunlight, especially on hot days. Car exhaust fumes produce such hydrocarbons. Ozone can worsen asthma and other respiratory problems in vulnerable people and is more prevalent in urban areas with more traffic.

Extreme heat can also affect respiratory health on its own or in combination with high levels of ozone.

Schwarz’s team notes that vulnerability to the excess heat / ozone combination appears to be decreased in wealthier zip codes, and the results correlate with factors that include better access to healthcare, lower stress levels, and more exercise.

“Considering the zip code level, some areas observed strong joint effects,” the study authors said. “A lower median income, a higher percentage of unemployed residents, and exposure to other air pollutants in a postal code resulted in stronger co-effects; a higher percentage of commuters who walk / cycle, a marker of neighborhood wealth, showed diminished effects.


Besides Schwarz and Benmarhnia, the authors include Kristen Hansen from the Herbert Wertheim School of Public Health and Human Longevity Science at UC San Diego, Anna Alari from the Sorbonne University in Paris, Sindana Ilango from the University of Washington, Nelson Bernal from the University of Brasilia in Brazil, Rupa Basu from the California Environmental Protection Agency and Alexander Gershunov from the Scripps Institution of Oceanography at UC San Diego.

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