Traffic is a major source of harmful pollutants; daily peak exposures tend to occur near roadways or while traveling—or being stuck—on them. For example, a team at the University of Surrey found that particulate pollution levels inside cars are up to 40% higher when the vehicle is stuck in a traffic jam or stopped at a red traffic light compared to free-flowing traffic conditions. (Earlier post.)
A team at the University of Washington in St Louis has now measured simultaneous real-time particulate matter (particle numbers, lung-deposited surface area, PM2.5, particle number size distributions) and CO concentrations outside and in-cabin of an on-road car during regular commutes to and from work. Data was collected for different ventilation parameters (windows open or closed, fan on, AC on), while traveling along different road-types with varying traffic densities. They found that car drivers can expect their highest exposures when driving with windows open or the fan on, and their lowest exposures during windows closed or the AC on. Their paper is published in Atmospheric Environment.
Anna Leavey, a research scientist at the School of Engineering and Applied Science, and Nathan Reed, a PhD candidate, worked together with PhD candidate Sameer Patel and Pratim Biswas, the Lucy and Stanley Lopata Professor and chair of the SEAS department of Energy, Environmental and Chemical Engineering. With assistance from Biswas’s Aerosol and Air Quality Research Lab, they used portable instruments and sensors to monitor and simultaneously measure the pollutant levels of their car’s indoor cabin air and the air directly outside of the car during their own daily commutes. That gave them rare, real-world look at pollutant exposure.
Using their simultaneous measurement approach, Leavey and Reed were able to test a number of variables while driving to and from Washington University over a four-month period starting in 2014. Using a dashcam, they were able to identify a given pollutant concentration each time they were: stuck behind a bus or truck, amid traffic on a freeway, stopped at a red light, or driving past restaurants or construction work. They also used different ventilation settings inside their cars: driving with the windows open, windows closed, with fan on, and with the air conditioning on.
Among their findings:
Ambient pollutants (NOx, PM2.5, CO) and meteorological variables (wind speed, temperature, relative humidity, dew point) explained 5–44% of outdoor pollutant variability, while the time spent traveling behind a bus was statistically significant for PM2.5, lung-deposited surface area (SA), and CO.
Time-series analysis demonstrated that cabin concentrations tended to track measured outdoor concentrations albeit with some reduced variability and time-lags when windows were open.
The geometric mean diameter (GMD) for outdoor aerosol was 34 nm. Larger cabin GMDs were observed when windows were closed compared to open (b = 4.3, p-value =