Wildfire smoke and debris has intensified attention on air quality and the local impact. While we monitor our latest forecasts, Social Explorer’s tools and resources can help add historical and geographical context to air pollution and its effects on communities.
Social Explorer’s environmental data resources include the EPA’s Air Quality Index (AQI). The dataset spans from 1980 to 2024, offering 45 years of data and trends. The extensive dataset includes median AQI, maximum AQI, days with unhealthy air quality, and breakdowns by pollutant type.
The July wave of wildfire smoke affected large regions of the country, especially the West, Midwest and Northeast. With Social Explorer, we can focus our analysis on the national picture as well as the hardest-hit areas. AQI readings from July 16th in Detroit (Wayne County) and Chicago (Cook County) were more than twice as high as a "hazardous" rating. Minneapolis (Hennepin County) also experienced record AQI numbers. These are just a few of the cities dealing with air quality dangers. The EPA’s AQI data in Social Explorer from up through 2024 show just how extreme this latest round of wildfires has been. The AQI categories follow EPA thresholds: Good (0–50), Moderate (51–100), Unhealthy for Sensitive Groups (101–150), Unhealthy (151–200), Very Unhealthy (201–300), Hazardous (301+).
The following chart of AQI data shows variability over a 10-year period, but all three counties hit their highest Max AQI values in 2023 during a prior wave of Canadian wildfires, with Hennepin County peaking at the highest level among the three.
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The AQI dataset includes detailed information on different types of pollutants from the EPA, including Carbon Monoxide (CO), Nitrogen Dioxide (NO2), Ozone, Particulate Matter 2.5 micrometers or smaller (PM2.5) and Particulate Matter 10 micrometers or smaller (PM10). Wildfire smoke contains tiny particles from ash, minerals and other debris, which has led to a large increase in PM2.5. This pollutant can be inhaled deeply and cause health problems.
The EPA AQI dataset also includes information on which pollutant was the dominant driver behind the daily AQI reading.
PM2.5 monitoring was not widespread until the late 1990s (the EPA established the PM2.5 standard in 1997). Looking at a decade of data, PM2.5 was the dominant rising trend — climbing from ~145 days in 2014 to a peak of ~161 days in 2023, driven largely by increasing wildfire smoke. The dramatic increase in wildfire smoke particularly originated in Western states, which became a dominant PM2.5 source from the mid-2010s onward. The following chart shows PM2.5 days for the three counties over the past few years.
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Wayne County consistently records the most PM2.5 days each year, reflecting Detroit's industrial and traffic pollution profile (vehicle exhaust is another source of the pollutant).
The chart’s pattern looks promising when PM2.5 days dropped sharply across all counties and the entire nation in 2024, but closer examination adds more to the story. That year stands out as an outlier across all pollutants, likely reflecting a milder wildfire season and favorable meteorological conditions rather than a confirmed structural improvement. When available, new dataset releases would add more context and trend analysis.
Please note that the AQI data includes monitored days only. Counties without monitoring on a given day are excluded from the count, so the total number of days may not sum to 365. The network of monitored counties grew by 50 from 934 in 2014 to 984 in 2024, a 5.4% increase. The expansion was steady and gradual, averaging about five new counties per year. This is worth keeping in mind when interpreting the pollutant day trends: a slightly larger monitoring network means more counties contributing to the averages each year, which can modestly inflate national totals over time — though the effect is small given the incremental pace of growth.
Environmental Justice Context with EJSCREEN:
Environmental justice data adds insight to the impact of environmental hazards such as wildfire smoke events. Social Explorer’s updated version of the EPA EJSCREEN dataset gives users data and mapping tools to identify communities most at risk. EJSCREEN data is available at the block group, census tract, county, and state levels, making it useful for neighborhood-level environmental justice analysis.
The EJ Index multiplies the environmental indicator (such as AQI measurements) by the demographic index. The demographic factors include percent of residents living below twice the federal poverty line and the percent of residents who are people of color.
A high EJ Index percentile (e.g., 95th) means the area faces both elevated PM2.5 exposure AND a high demographic burden — this is the population EPA considers most at risk and most in need of regulatory attention. The EJSCREEN’s PM2.5 estimates come from the EPA's Fused Air Quality Surface Using Downscaling (FAQSD), using satellite data, air quality models, and ground-level monitor readings.
The following map shows the EJ Index for PM2.5 at the county level across the nation.
Wayne County ranks in the 96th percentile nationally, meaning it scores higher than 96% of all counties on the combined PM2.5 and demographic vulnerability index. This reflects both elevated particulate matter exposure and a high concentration of socially vulnerable residents.
Cook County is close behind at the 94th percentile, also indicating a significant environmental justice concern for PM2.5.
Hennepin County scores considerably lower at the 34th percentile, suggesting relatively lower combined PM2.5 burden and/or lower demographic vulnerability compared to the national distribution.
Zoom in on the map to explore more trends and parts of the country.
Analyze More Environmental and Demographic Data with Social Explorer:
Social Explorer’s extensive library of air quality data adds context to the latest wildfire smoke we’re experiencing this summer. Additionally, our environmental justice data help provide insight into community level impacts.
Social Explorer’s data library offers resources for planners, researchers, advocates, news media, and more.
Subscribers can get started with our environmental data today. Let Social Explorer’s tools enrich your planning, grantwriting, advocacy, and other research.
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