Air Quality

Air Quality Extremes in 2020: More “Good” Days and More “Unhealthy” Days

Poor air quality can aggravate the symptoms of heart and lung ailments, including asthma. It can also cause irritation and illness among the healthy population. Long-term exposure increases the risks of lung cancer, cardiovascular disease, and many other health conditions. Poor air quality can also put children’s lung development at risk. This indicator uses the Air Quality Index (AQI) to measure air quality in San Bernardino County, neighboring California counties and peer regions outside of California.

How is San Bernardino County Doing?


The most common air quality status for San Bernardino County is the “moderate” range. In 2020, one-third of days (32%) were in the “moderate” range, which was substantially fewer than the 48% of days reported in 2019. The second most common air quality status in 2020 was “good,” which accounted for 22% of days of the year, which is an improvement compared to 2019 when 15% of days were “good.” One in five days (or 21% of days) were considered “unhealthy for sensitive groups” in 2020, which was similar to the percentage in 2019 (19%). Meanwhile, 20% of days were “unhealthy” in 2020, compared to 15% in 2019. Air that was “very unhealthy” rose from 2% of days in 2019 to 6% of days in 2020. Overall, the median Air Quality Index value increased in 2020 to 97, up from 80 in 2019. Both values are in the “moderate” range.


San Bernardino County, 2013-2022*

* Data for 2022 are preliminary, which is denoted using dotted lines in the chart. The percentages were calculated on 332 days with AQI data in 2022, whereas the remainder of the years shown were calculated with 365 (or 366) days with AQI data. The 2022 data were retrieved January 22, 2023 and subject to change.
Source: U.S. Environmental Protection Agency, Air Data (


Looking at peer regions, there is variation in the number of days each region experiences in the five Air Quality Index categories – from “good” to “very unhealthy.” However, the median Air Quality Index value, which takes into account all daily AQI readings in a given year, was higher in San Bernardino County in 2019 than all regions compared. Regional comparison data from 2019 are presented due to the preliminary status of 2020 data.


Regional Comparison, 2021

Note: The regions are sorted from top to bottom according the median air quality index value in each region, from highest to lowest. These data are based on hourly monitor data to assess air quality, resulting in more days of unhealthy air than data that is used by air quality management districts for regulatory compliance, which uses 24-hour monitor values.
Source: U.S. Environmental Protection Agency, Air Data (