What a difference a freeway makes; highway closure improves air quality by 83%

In study findings announced today UCLA researchers report that air quality near the closed section of highway 405 last year improved within minutes, reaching levels 83 percent better than on comparable weekends.

 

Because traffic dipped all over Southern California that weekend, air quality also improved 75 percent in parts of West Los Angeles and Santa Monica and an average of 25 percent regionally — from Ventura to Yucaipa, and Long Beach to Santa Clarita.

 

The study was led by two professors at UCLA's Institute of the Environment and Sustainability: Yifang Zhu, who is also an associate professor of environmental health sciences at the UCLA Fielding School of Public Health, and Suzanne Paulson, who is also a professor of atmospheric and oceanic sciences.

While the researchers expected cleaner air, they didn't expect the improvement to be so dramatic.

 

"The air was amazingly clean that weekend," Paulson said. "Our measurements in Santa Monica were almost below what our instruments could detect, and the regional effect was significant. It was a really eye-opening glimpse of what the future could be like if we can move away from combustion engines."

 

The research gives a peek at what the air would look like in a healthier Los Angeles with a vast majority of hybrid and electric vehicles and shows how quickly less driving can improve key measures of air quality.

 

Taking measurements

The researchers measured ultrafine particles (less than 0.1 microns in diameter), which are key indicators of real-time traffic levels, and also fine particulate matter known as "PM2.5" (less than 2.5 microns in diameter), which includes tailpipe emissions and new particles created when the emissions interact with the atmosphere. PM2.5 can spread farther from the freeway and last longer than ultrafine particles, but both are pollutants with health risks. Exposure to near-roadway pollutants has been linked to increases in asthma, heart attacks, strokes, diabetes, low birth weight, pre-term births and other ailments, the researchers noted.

 

Zhu and Paulson found that when traffic dropped more than 90 percent on the closed 405, with only construction vehicles still on the move, ultrafine particles dropped by 83 percent. PM2.5 concentrations dropped 36 percent.

 

More broadly, ultrafine particles and PM2.5 levels dropped 75 percent across a swath of West Los Angeles near the I-405/I-10 interchange stretching from Santa Monica to Westwood. Elsewhere, they measured PM2.5 and found the air 31 percent cleaner in Ventura, 19 percent cleaner in Yucaipa, 30 percent cleaner in Long Beach, 23.2 percent cleaner in Santa Clarita and 19.9 percent cleaner in Northridge.

 

"There is no safe level of PM2.5 concentrations, where you would no longer observe health impacts, so any reduction is an improvement," Zhu said. "This study shows that with such dramatic traffic reductions, there are specific air-quality improvements. It gives policymakers and the public incentives to put more effort into reducing traffic emissions."