Air Quality in USA Metro Areas

Project Summary

My project is to evaluate geographical phenomena that changes over time by creating an interactive map. I chose to evaluate air quality in the United States. The EPA provides data on air quality using a term called AQI, and publishes data by metro area and for a variety of time periods.

I evaluated air quality in the United States in three ways: Median AQI calculated annually, monthly, and daily.

Important terms:

AQI

The Air Quality Index (AQI) is an aggregated term to evaluate air quality from multiple air pollutants. The EPA AQI is grouped into one of six categories based on its value and associated health risks. A lower AQI corresponds to cleaner air, with little pollution, and a higher AQI corresponds to unhealthy air. For each pollutant, a value of 100 generally corresponds to the national air quality standard for public health. The AQI categories are color-coded: green is good, red is bad, maroon is hazardous.

CBSA

U.S. EPA Core Based Statistical Area (CBSA) is a term used for metro areas. I narrowed my analysis to the top 40 most populated metro areas.

Median Annual AQI in USA Metro Areas 2000-2022

This map looks at trends in the median AQI value over the whole year, for the years 2000-2022.

AQI is known to vary quite drastically daily, monthly, seasonally, and in response to accute events (wildfires, for example), and thus AQI is typically evaluated with more granualar time data. This map explores AQI with "course" time data, looking at the median value over a full year.

This analysis shows the yearly median AQI is relatively consistent in metro areas between years. We also see AQI values generally decrease across all metro areas.

Median Monthly AQI in USA Metro Areas 2021

This map evaluates AQI trends in the same metro areas as the first map, but with median AQI calculated per month in 2021.

The year 2021 was chosen because it is the most recent full year of data published, using daily AQI data that I consolidated into months. The monthly AQI data is more varied than yearly data. The strongest geographic pattern seems to be AQI is higher in the southwest. This data also shows higher AQI in the summer season, which is a known pattern with air quality: AQI is usually worse with high heat.

Median Daily AQI in USA Metro Areas 2021

This map evaluates AQI trends in the same metro areas as the first two maps, but with median AQI calculated per day in 2021.

The time data for this map is much "finer" than the previous two. I wanted to see if I could capture the day to day variations in AQI in comparison to the more consistent monthly and annual data. The result is a little visually overwhelming, but we do see that AQI can vary drastically in any metro area. We also see more frequent spots of high AQI in the summer months across many metros.

This data shows Arizona and California have consistently high AQI values. Metros in these states tend to be highly populated with warm and dry climates. They are particularly susceptible to effects from high heat, urban emissions, and wildfires.