Overall air quality is improving in the U.S, thanks to a combination of stricter environmental regulations, cleaner technologies and other factors. Levels of particulate matter have fallen by around 50% over the past 30 years in most areas.
However, Los Angeles still ranks among the worst.
How many hours are you exposed to clean air in your neighborhood? We examined the air quality of 251 neighborhoods, cities and towns across LA county hour by hour for almost an entire year.
We looked for the areas where air quality (concentrations of PM 2.5) was frequently below 50 on the Air Quality Index scale, which is considered healthy. We examined 6802 hourly readings between November 2016 and October 2017.
What we found:
A note of caution: There are many variables that determine air quality. Measuring the number of hours that a neighborhood experiences high or low levels of PM 2.5 is only one way of understanding the differences in air quality among areas in Los Angeles. Areas that have consistently low levels of PM 2.5 may also have other characteristics that could impact overall air quality.
1. Altadena. 3878 hours
Altadena, at the edge of the Angeles National Forest, is first on our list. It had 3878 hours of good air quality out of our observed 6802 hours.
2. Glendora. 3798 hours
Glendora, also near the southern border of the Angeles National Forest, comes in second place.
3. Lopez/Kagel Canyons. 3703 hours
This area sits in the steep terrain of the San Gabriel foothills. However, it was also the site of the recent Creek Fire, which occurred after our data-collection period.
4. Pacific Palisades. 3700 hours
Los Angeles’s Pacific Palisades neighborhood is buffeted by ocean breezes and has no major freeways running through it.
5. Lake View Terrace. 3696 hours
This Los Angeles neighborhood is tucked in between two regional parks at the foot of the San Gabriel Mountains.
Here’s a list of other neighborhoods which frequently register good air quality based on our data:
6. Val Verde: 3679 hours
7. La Habra Heights: 3679 hours
8. Westlake Village: 3679 hours
9. Tarzana: 3677 hours
10. Brentwood: 3676 hours
11. North Whittier : 3676 hours
12. La Crescenta-Montrose: 3674 hours
13. Duarte: 3671 hours
14. Bel-Air: 3670 hours
15. Griffith Park: 3661 hours
16. Encino: 3659 hours
17. Rolling Hills: 3658 hours
18. La Verne: 3655 hours
19. Stevenson Ranch: 3651 hours
20. Highland Park: 3646 hours
How we did it:
We collect hourly readings of PM 2.5 levels (particles smaller than 2.5 µm in aerodynamic diameter) from the 12 monitoring stations of the Environmental Protection Agency and the South Coast Air Quality Management District located throughout Los Angeles County. The air quality data is updated every hour. The data we receive is based off of raw PM 2.5 measurements that have been converted to the Air Quality Index scale. PM 2.5 levels are generally proportional to AQI. (However, the actual AQI number is calculated using several different variables and is a 24-hour average.)
We then use a process developed by our partners at the USC Spatial Sciences Institute that takes into account the surrounding geographic context of every neighborhood or area in the entire county of Los Angeles. We use geographic data from OSM (OpenStreetMap) to generate a “geographic abstraction” for each monitoring station automatically. The geographic abstraction is used to describe the neighborhood environment for a given location. For example, we compute the built environment, including the length of various road types, the point number of various locations types, area of open spaces, and so on. Then we build geo-context by selecting important features based on the air quality data.
We create a fishnet of grid points across Los Angeles County. With the geo-context, we are able to compute PM2.5 values for the locations in the fishnet that do not have monitoring stations. We have around 3,000 points in total, four points within one square mile. For each point, we predict an hourly PM 2.5 AQI. We then map that against library of neighborhood boundaries created by The Los Angeles Times.
Have questions? Write us at firstname.lastname@example.org
*This post was updated on June 21 to include language that better reflects the degree to which this analysis can be interpreted.