Operation Healthy Air Report Now Available!

In 2017, a team of community members, scientists, and local organizations came together to assess local air temperature and ozone changes from yard to yard, and from neighborhood to neighborhood in Southern California to help inform how best to adapt to dangerous levels of pollution and severe heat. Operation Healthy Air (OHA) engaged more than 1,000 community members who contributed their time, energy, and insights to collect data at over 230 sites. Our team has started to analyze the data and has presented some preliminary results in this newly released report.


Climate change is predicted to exacerbate health challenges in cities, especially the conditions that impact poor communities most. Generally, attention and funding are drawn to the catastrophic events associated with climate change, such as coastal storms and areas with high risk for financial losses. However, urban and heavily developed suburban communities are subjected on a daily basis to the effects of climate change in the form of high temperatures which when combined with reduced air quality promote chronic health problems.

Ozone Levels

The rate of death due to high Ozone levels is higher in cities (LA/Long Beach) compared to less urban environments (Riverside/San Bernardino). Ozone is formed when the right ratio of specific types of air pollutants are exposed to sunlight and heat. Ozone is a toxic pollutant that irritates and damages lungs and other tissues.

Deaths per year due to high Ozone levels:

  • 3,255 for Los Angeles – Long Beach – Glendale
  • 1,416 for Riverside – San Bernardino – Ontario area

Number of times people called in sick, missed school, etc. because of air pollution:

    • 2.9 million dates in LA
    • 1.3 million in the inland area

Ozone levels change significantly based on temperature and wind direction. Residents should avoid being outdoors during the hottest parts of the day to avoid the highest concentrations of ozone in the air.

Tree Coverage

Tree coverage is essential for maintaining cooler temperatures and cleaner air. We also found that tree size matter in helping to cool local air significantly, but only during the day. At night, the amount of pavement (especially asphalt, i.e. roads) influences temperature most.

Indoor Temperature

We also examined peoples comfort levels based on indoor temperatures. Managing indoor air temperature can minimize carbon footprint and cost. This study has demonstrated that even small differences in temperature have an impact on our comfort so paying attention to local temperature can improve your health and ability to function well. Research has also shown that people can become acclimated and adjust their temperature comfort threshold—so it is possible to adapt to warmer temperatures within reason. Try to adjust indoor air conditioners down one or two degrees to see if you can become acclimated. If that works, try to adjust down again and see what happens.

Get detailed insight into why this program was started, what setting up a study looks like, and how we implemented a large-scale research program with the help of community members.

Read the Report Here

Water Usage vs. Tree Growth: The Ecological Trade-Off of Urban Trees in Southern California

By Peter Ibsen, Ph.D. Candidate; Department of Botany and Plant Science, University of California Riverside

For the past several years, I have taught ecology classes to hundreds of undergraduate students at University of California Riverside and have found that the urban tree is an ideal common ground to discuss the ecological concept of “trade-offs.” You see, every single student has experiences with urban trees, from backyard lemons, to tire swings, to taking a nap in the shade of a sycamore on a hot day. Urban trees provide all these services and so many more, yet, the future of urban trees in dry regions is in doubt, and we, as urban residents, have to make serious considerations about ecological trade-offs between water usage and tree growth.

With the assistance of hundreds of citizen scientists, I am conducting a study of urban tree function across the climate gradient of Southern California. My early results find that the urban forest comprises a broad spectrum of ecological strategies regarding tree growth and water usage. It is possible to find species exhibiting all combinations of “fast/slow” growth and “liberal/conservative” water usage.

Figure 1. Ten species of urban trees oriented in an ecological trait space. Each quadrant represents a growth-to-water use strategy. Trees are represented using the US Forest Service IDs by species.

However, my research has discovered two very important trade-offs of water use and tree growth. When separating out the urban trees found in coastal southern California from those found in desert regions, what appears is an interesting difference between the two communities. The desert urban forest exhibits functions of a faster growth and liberal water usage. This goes against some conventional thinking that people plant more water-conserving trees in the desert. They key finding here is that trees and parks are heavily irrigated, and as long as a species can withstand the heat, they can take advantage of both the water and abundant sunlight for growth.

Figure 2: The effects of irrigation in Palm Springs. The difference between the irrigated Desert Highland Park and the natural Palm Springs environment on the right highlights this effect.

I also studied how individual species may change functional strategies when planted from the coast to the desert. By measuring the difference of plant water pressure before dawn (when plants have low water pressure) and in the middle of the day (when plant have higher water pressure), I am able to calculate the water status of a species at a certain location. A higher water status implies that the tree is losing more water to the environment. I discovered that all species studied, save one, increase their water usage when moving from a coastal environment to a desert one.

Figure 3: The differences in water status of California urban tree species. Most species exhibit an increase in water status when they are planted in the urban desert.

When taking all these results together, there is a clear management trade-off. In hotter and more arid environments, urban trees have the potential to experience faster growth at the expense of increased water usage. For urban stakeholders, this is serious consideration. Faster growth means quicker establishment of shade and greater cooling of air temperature. However, increased water usage has serious consequences for an area prone to extended droughts. As the future Southern California climate is predicted to become hotter and drier, our results highlight the uncertainty of our urban forest. My research will continue to add more species to the study, with a goal of both higher resolution of results, and ultimately an idea of which species might be “the right trees, for the right place, in the right time.”

And, thank you to all the community scientists who helped find the trees included in my study, including partners across the Greater Los Angeles region! Please let me know if you have any questions.