Title Image: Mexico City smog, 1981 G Lamson/CC BY-NC-SA2.0
Climate Change and Air Quality
In Part 1 of this post, we discussed the impact of the EPA’s commendable efforts to contain harmful pollutants and improve air quality in the U.S. Unfortunately, efforts to reign in climate change have been much less effective, with total greenhouse gas emissions reaching record levels in 2024.
The resulting changes to the global climate are having a direct impact on air quality and human health:
- Heatwaves and Urban Heat Islands are amplifying the effects of pollution on human health. 2024 was the hottest year on record. This was not an outlier — the last 10 years are the ten hottest ever recorded.
- Increasing heat in urban areas promotes development of harmful ground-level ozone.
- Drought has become a growing problem induced by heat and changing precipitation patterns. The consequent dust storms and wildfires can have a catastrophic effect on air quality and human health.
- Extreme wildfires are increasingly common in our warming and drying climate. The resulting smoke spreads far beyond the fire site, distributing PM10, PM2.5 and PM0.1 particulates, as well as toxic VOCs (Volatile Organic Compounds).
- Rising temperatures are amplifying the range and production of airborne bioallergens, including tree, grass and plant pollens, and mold spores.
Unfortunately, it’s very likely that things will get worse before they start to get better. We need to be prepared.
The rest of this post covers how you can evaluate and adapt to air quality issues in your location, and the specific health risks to watch out for in our changing climate.
EPA Air Quality Services – AirNow
Up to date, accurate information is key to an effective response to air quality problems. Fortunately, the EPA is doing an excellent job of making available actionable air quality information. The EPA’s primary communication vehicle is its AirNow service, which provides air quality information at local, state, national and international levels. AirNow is readily accessible via the AirNow website and mobile app,
The EPA justifiably promotes AirNow as “your one-stop source for air quality data.” AirNow provides access to:
- current and forecast air quality maps and data for 500+ cities across the U.S.
- current and historical data for U.S. Embassies and Consulates around the world
- current fire conditions including fire locations, smoke plumes, and air quality data
- air quality data for Canada and Mexico
- “Enviroflash” EPA notifications via email or mobile app
- a wide range of health and air quality information
As a simple example, we accessed the AirNow website and entered “Tampa, Florida” as our location of interest. The image below shows the initial result — the AirNow “dial.”
Figure 1: AirNow hourly report for Tampa, Florida at 2 pm, February 7, 2025. Credit: EPA AirNow
The dial displays “NowCast” near real-time information generated from hourly air quality monitor ozone and particulate data for the current hour. That data is used to calculate the AQI (Air Quality Index) for each of the ozone and particulate pollutants. The dial shows the data for the pollutant with the highest AQI for the hour, in this case PM 10, with an AQI of 58. The dial color corresponds to the AQI, using the color rating system discussed in Part 1 of this post and summarized in the figure below:
Figure 2: AQI rating scale Credit: EPA AirNow
The Tampa query also returned more detailed information about the overall air quality determined by the NowCast, including the map in Figure 3, showing that the yellow “Moderate” AQI is localized near Tampa, with the rest of the state experiencing “Good” conditions at the time of the query. Not shown but also provided is a less detailed daily forecast for the next five days, predicting the primary pollutant and its likely AQI daily average.
Figure 3: AQI’s for PM 10, PM2.5 and ozone “NowCast” for the 2pm hour, February 7, 2025 Credit: EPA AirNow
Last, but far from least, is the AirNow “Interactive Map,” shown below. The example map below shows the location of monitoring stations and their NowCast air quality rating, with color shading identifying areas forecast to exceed a “good” rating. The Interactive Map can be zoomed in to the level of a city street map.
Figure 4: AirNow Interactive Map example Credit: EPA AirNow
This is a small sample of the wealth of information freely accessible through the AirNow website or app. The key takeaway is that AirNow can pr0vide you with the information you need to decide if it’s OK for a child with asthma to play outside, or if a family member with a pre-existing condition would be in danger. AirNow enables dynamic climate adaptation at a human scale.
That’s the good news. Now let’s look at the health risks affected by the changing climate.
Heat and Air Quality
By itself, heat can have a serious impact on human health. When heat combines with air pollution, the impacts compound.
Extreme heat is by far the leading cause of weather-related deaths in the United States, according to the National Weather Service. High temperatures can lead to death, often in combination with pre-existing conditions like respiratory issues or heart disease. More fatalities are caused by extreme heat than by hurricanes and tornadoes combined.
Excessive heat has the greatest impact on those who are also the most vulnerable to poor air quality — people with pre-existing conditions, the elderly, children and pregnant women. When you combine extreme heat with health-threatening air quality, the danger intensifies. The cities of the desert southwest are a case in point.
And the western U.S. is warming dramatically. In 2024 Phoenix, Arizona set a record 70 days with highs of 110°F or more, and an overall average temperature of 98.3°. In 5 months spanning late 2024 and early 2025, Phoenix recorded no measurable rainfall – the city’s second longest dry period on record.
Extreme heat in southwestern cities like Phoenix or Reno, Nevada combines with dry air and abundant sun to supercharge ozone pollution. Heatwaves and heat domes create ideal conditions for ozone generation: heat, clear sky (lots of sunlight), and stagnant air. The typical result is shown in Figure 5, below.
Figure 5: Smog over Phoenix, Arizona in 2006 Credit: Deirdre Hamill/The Republic
In its 2024 State of the Air report, the American Lung Association ranked the most-polluted U.S. cities. Of the 228 cities ranked by ozone pollution, Phoenix was #5 (Los Angeles-Long Beach was #1).
Another feature of the steadily warming climate in the western U.S. is the multi-decadal western US megadrought. Recent research shows that the warming atmosphere, increasing the amount of moisture lost by evaporation, is now the principal factor worsening the drought (rather than decreasing precipitation.)
Heat and persistent drought set the stage for dust storms. The high winds of a dust storm can carry a tremendous quantity of PM 10 particulates.
Figure 6: Phoenix dust storm, August 22, 2024 Credit: Jason Morrow/NWS
Figure 6 shows a Phoenix dust storm driven by powerful downdraft winds fanning outward from a violent thunderstorm. Dust-laden winds in excess of 50 mph reduced visibility to less than a quarter of a mile.
A powerful dust storm in a hot, dry climate is just the sort of event that compounds existing conditions and pushes the vulnerable “over the edge” and into the hospital
Allergens and Asthma
Airborne allergens (e.g., grass, weed and tree pollen, mold, dust mites) are another form of “air pollution” with implications for human health.
Allergies and asthma are both respiratory conditions that can cause breathing difficulties. but they have distinct characteristics and triggers. Allergies primarily affect the upper respiratory tract with an immune system reaction to an allergen. Asthma primarily affects the lower respiratory tract, where the airways become inflamed and constricted.
In the U.S., 26% of adults have seasonal allergies, while 28 million people have asthma. Many have both. An estimated 40% of Europeans have a pollen allergy.
Pollen allergies are typically seasonal and location-dependent, and thus health impacts are relatively short-lived.
On the other hand, asthma is a chronic condition that can worsen over time. Airborne allergens can trigger an “asthma attack”— intensified breathing difficulties caused by further narrowing and inflammation of the airways in the lungs. Asthma can also be triggered by air pollution, physical exertion, stress, smoke, viruses and weather.
The U.S. Department of Health and Human Services reports that pollen concentrations across North America are increasing, as climate change leads to earlier and longer pollen seasons and higher pollen counts. Climate change is causing shifts in precipitation patterns, more frost-free days, and a longer growing season, while warmer seasonal air temperatures, and more carbon dioxide (CO2) in the atmosphere stimulate plant growth. At the same time, a warming climate and a lengthening growing season can enable plant species that release allergenic pollen to migrate into previously inhospitable environments.
Global warming and the associated lengthening of the growing season facilitate a northward migration of invasive plant species in Europe, also those releasing allergenic pollen. The introduction of new allergens can increase local sensitisation, i.e., the process of people becoming sensitive or allergic due to exposure to allergens (Confalonieri et al., 2007).
Figure 7: Spring 2024. Red areas on the map indicate an earlier than average start of plant growth and thus an earlier start to the pollen season Credit: U.S. HHS
The map above clearly shows an earlier than average onset of spring in 2024 across the U.S. Areas along the west coast, parts of the Plains states and the southern Midwest experienced the earliest start to spring on record. Allergy season followed close behind.
The health effects of allergies are more complex in urban environments, where simultaneous exposure to pollutants such as ozone and nitrogen dioxide can make allergic reactions worse.
Between 1990 and 2018, total pollen amounts in the U.S. increased by up to 21%, accompanied by a longer pollen season. Both pollen concentrations and the pollen season are expected to increase alongside continued climate warming.
Wildfires and Air Quality
In many ways, wildfires are the poster child of climate change. The occurrence of “Fire Weather,” the combination of persistent drought, heat, and low humidity that sets the stage for wildfires, is increasingly common as a result of climate change. As we saw in Los Angeles in 2025, dry, hot and windy weather combined with tinder-dry vegetation increases the likelihood of extreme wildfires.
The health impact of wildfires is significant. Wildfires generate a broad range of hazardous particulate matter, black carbon, carbon monoxide, nitrogen oxides, volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs.)
VOCs have been associated with a range of health impacts, including respiratory problems, damage to the liver, kidneys or central nervous system. PAHs are carcinogenic.
The impact of climate change was highlighted in a recent study that showed both the frequency and the intensity of extreme wildfires (the top 0.01%) around the world more than doubled from 2003 to 2023. About 3,000 fires were identified as “extreme” in the study. The global increase in the frequency and intensity of wildfires was primarily due to changes in two regions, the temperate coniferous forests of the western U.S. and Canada, and the northern boreal forests of North America and Russia. In the western U.S. and Canada, the number of extreme fires increased by more than 11 times, from 6 in 2003 to 67 in 2023. The boreal forests experienced a 7.3-fold increase over the same period.
The impact of wildfires on U.S. air quality is illustrated in the graph below.
Figure 8: Dramatic increase in exposure to wildfire-generated PM2,5 in the U.S. Credit: Climate Central
A recent study found that by 2020, the number of people exposed to at least 1 day per year of smoke PM2.5 three times the EPA safe standard per year had increased 27-fold since 2010 — nearly 25 million people in 2020 alone. Climate Central determined that Canadian wildfires in 2023 pushed per-capita smoke pollution exposure in the U.S. to more than double 2020 levels.
Wildfire smoke is easily transported, as we found in 2023, when the Eastern seaboard of the U.S. was blanketed by dense smoke from Canadian wildfires.
Figure 9: Dense smoke from wildfires in northern Canada envelops New York City in 2023
EPA AirNow Wildfire Services
The EPA, partnered with the U.S. Forest Service, provides a wealth of wildfire and smoke information in near real-time. The principal tool is the interactive “Fire and Smoke Map”, a variant of the AirNow Interactive Map.
The Fire and Smoke Map shows:
- Air quality rating for fine particle pollution (PM2.5), the key pollutant in smoke
- Steps you can take to reduce your smoke exposure
- Information about whether air quality is getting better or worse
- Smoke plumes
- Fire locations
- Smoke forecast outlooks
The image below is a 2023 Fire and Smoke Map for the northeastern U.S. during the peak of the Canadian forest fire season.
Figure 10: EPA Fire and Smoke Map for the Northeastern U.S. and Eastern Canada during the 2023 fire season. The grey shading shows the extent and severity of the smoke plume, while the colored dots show the AQI at monitoring stations. (Note that several Canadian monitoring sites near the center of the map show a “hazardous” AQI rating – greater than 300! Credit: EPA AirNow/U.S. Forest Service
Selecting any monitoring sites on the Fire and Smoke Map will bring up the detailed, actionable information, as shown in Figure 11.
Figure 11: Fire and Smoke Map monitoring station information. Bend, Oregon, October 2024 Credit: EPA AirNow/U.S. Forest Service
In this case, the monitoring station indicates an “unhealthy”/red (AQI 150-200) level of PM2.5 in the last hour. The NowCast chart shows that conditions could be much worse on October 14th, with a prolonged period of “very unhealthy”/purple (AQI 201-300). Note that there is not a fire near the monitoring station, located on the outskirts of Bend, nor is there a smoke plume detected. However, the panel at the bottom of the station report does advise that there are fires southwest and west-southwest of town.
This is tremendously valuable information that enables informed, personal decision-making. Perhaps:
- you should set the air conditioning in “recirculate” mode
- your asthmatic child walks to school. Better keep them home tomorrow and cancel your golf game
- your business trip to Bend might need to be rescheduled
- you’d better stock up the pantry in case you’re shut in for a day or two
And should you decide to leave town for a safer location, the map will help you plan a route that avoids fires and smoke.
The Takeaway
Climate change is having a direct and significant impact on air quality, and thus on human health. The impact of climate change is far reaching and increasing. In the U.S., the EPA, in cooperation with other federal, state and local entities, is doing its best to provide information that empowers individuals to manage their exposure to air quality levels harmful to humans health. However, unless we halt human-caused climate change, air quality will deteriorate and so will human health.