A11M-0234
Using CO to NOX Ratios to Understand the Impact of Photoactive Roadways on Urban Atmospheric Chemistry and their Efficiency in Mitigating Air Pollution
Monday, 14 December 2015
Poster Hall (Moscone South)
Claudia Toro1, Bertram Tom Jobson2, Serena H Chung2, Liv Haselbach2 and Shihui Shen3, (1)Washington State University, Laboratory for Atmospheric Research - Department of Civil&Environmental Engineering, Pullman, WA, United States, (2)Washington State University, Pullman, WA, United States, (3)Pennsylvania State University Main Campus, Business and Engineering, Altoona, PA, United States
Abstract:
Photoactive roadways and the incorporation of diverse photocatalytic surfaces into the built environment have been proposed as a strategy to improve air quality in urban areas. Laboratory studies show that surfaces treated with TiO2 are efficient in removing nitrogen oxides (NOX). Nonetheless, measurements under ambient conditions capable of isolating the impact of the photoactive surface are scarce. Previous work by our group demonstrated that CO remains stable during the timescale where NOX removal is detected, and thus can be used as a tracer. The work presented herein focuses on outdoor tests comparing CO to NOX ratios (CO/NOX) before and after interacting with photoactive pavement materials. The samples were placed in a Teflon chamber receiving a controlled flow of ambient air supplemented with a constant addition of CO and NO calibration gases. Experiments started before sunrise and continued until sunset to understand the variation due to changing UV levels. CO and NOx were monitored at the input and output of the chamber; O3 was monitored at the input. Preliminary results with asphalt roadway samples indicate that while the input CO/NOX remains constant during the day, the output CO/NOX shows a maximum during early morning and subsequently decreases to a steady value throughout the afternoon. Our previous laboratory work indicates that NO2 removal by photoactive asphalt is smaller than that of NO. We hypothesize that the decrease in the CO/NOx ratio after early morning hours is caused by 1) the enhancement in O3 concentrations as the atmospheric photochemistry increases resulting in more NO2 entering the chamber and 2) NO2 released during photocatalytic NO removal process. Therefore, as the NO2/NO increases, the efficiency of photoactive process decreases indicating that the potential benefit from photoactive roads would likely be driven by a balance between UV levels and local photochemistry.
