Overview: California Cities AQI from 1980 to 2022

This dashboard is using a subset of data from the CalEnviroScreen (CES) 4.0 data set, produced by the California Office of Environmental Health Hazards Assessment (OEHHA).

This subset of data is observing Air Quality Index (AQI) reports from 31 cities throughout the state between the years 1980 and 2022. With this data, we are observing the change in average AQI per city over time, specifically questioning changes in variance over time, as well as potential impacts from geographic location and population size. This AQI data tells the story of improving air quality over time throughout the state of California. The following cities are featured in the data set:

• Bakersfield
• Bishop
• Chico
• Crescent City
• El Centro
• Eureka
• Fresno
• Hanford
• Los Angeles
• Madera
• Merced
• Modesto
• Napa
• Oxnard
• Red Bluff
• Redding
• Riverside
• Sacramento
• Salinas
• San Diego
• San Francisco
• San Jose
• San Luis Obispo
• Santa Cruz
• Santa Maria
• Santa Rosa
• Sonora
• Stockton
• Susanville
• Truckee
• Ukiah
• Vallejo
• Visalia
• Yuba City

The research question for this dashboard is, how do time, geographic location, and population size act as factors in the development of AQI reports in the cities in the CES 4.0 dataset over the reporting period from 1980 to 2022?

Average AQI and Dominant Category by City

The figure below maps out the location of each of the 31 cities from the CES 4.0 data set, with bubble size representing the average AQI reported for that city during the indicated time period. The color of the bubble indicates the AQI category for each city’s average. The five layers for the map represent five different time frames, four periods of seven years and one period of ten years (the most recent period is the longest).

Violin Plot: AQI Distribution by Time Period

This graph observes the distribution in AQI reports over time, grouping the time period of 1980-2022 into four seven-year periods and one ten-year period (rounding the most recent years together). Hovering over the figures in the violin plot below, we can see that the mean and median AQI remains relatively consistent throughout each time period, but the variance between the minimum and maximum reported values shrink as time goes by.

Scatterplot: Average Annual AQI by City

This graph demonstrates the progression over time of the annual average AQI for each of the 31 cities included in this data set. Bubbles are sized based on city population, and colored based on the AQI category of the annual average. Like the violin plot, we can observe that over time, the variance of the reported average AQI across the cities in this data set shrinks, increasing overlap in the data points.

Results/Conclusion

The decrease in variance over time suggests that over time, air quality challenges have reduced over time across the board in California. The mapping tool seems to suggest that there is a slight regional correlation, with southern cities reporting higher AQIs on average throughout each time period. Cities with larger populations also appear to have consistently higher AQIs than cities with lower populations, but it is worth noting that by the turn of the 21st century, many high population cities were reporting similar AQIs as their less populated counterparts.

There is a noteworthy opportunity to explore what policy measures were taken from 1980-2000 which may have resulted in a state-wide decrease in annual average AQI reporting, and how those measures may have been able to have an impact across the board, regardless of factors such as geographic location and population size, seeing as these two factors seemed to have decreasing impact on the trends for each of these visualizations over time.