Vehicle emissions are a major source of urban air pollution in cities worldwide and major contributors to ground level ozone pollution. One effort taking hold to improve air quality in cities is the application of titanium dioxide to building and roadway surfaces to make these surfaces photocatalytic. Upon irradiation with sunlight, these surfaces efficiently destroy nitrogen oxides (NOx) and volatile organic compounds (VOCs), the precursors to ozone. While such surfaces have been shown to be effective at removing NOx, there has been no systematic study to quantify their potential to reduce human exposure to ozone and to the toxic compounds emitted in vehicle exhaust. These surfaces may in fact generate air toxics such as nitrous acid from NOx, and formaldehyde and acetaldehyde from VOCs. Preliminary studies by our group have shown that formaldehyde and acetaldehyde are rapidly generated when gasoline vapor mixtures are exposed to illuminated titanium dioxide treated concrete. Photoactive roads may in fact increase ozone in urban areas by decreasing the NOx / VOC concentration ratio and increasing radical production rates via production of nitrous acid and formaldehyde.
Understanding the net effect of vehicle exhaust transformation on these surfaces is essential for determining if photoactive urban materials will in fact improve urban air quality. In this project chamber studies will be used to quantify NOx and VOCs loss to photoactive roadway materials (asphalt and concrete) as a function of light levels, temperature, humidity, and commercial titanium dioxide surface treatment products. The yields of nitrous acid and aldehydes will also be measured. Chamber tests will be conducted on prepared test mixtures that mimic vehicle exhaust including gasoline vapor and in outdoor experiments under ambient pollution conditions. The surface destruction efficiencies of NOx and VOCs and yields of nitrous acid and aldehydes will be parameterized and used in an air quality model to test the resulting impact on primary pollutant concentrations and ozone formation photochemistry. This project would provide the first systematic investigation and integrated air quality numerical modeling study of the impact of photoactive roads on urban air chemistry.
This study will provide much needed quantitative information of interest to the public and urban planners on the efficacy of photoactive roads as a solution to reduce urban air pollution. Exposure to vehicle exhaust has been shown to have a significant impact on cardiovascular health. Removing vehicle pollutants at the source with photoactive roads has the potential to improve health for millions of people living near major roadways. The results of the research will be used in undergraduate course work and disseminated in conferences and peer reviewed publications. The research will help support one graduate student and provide support for a summer research internship for an American Indian student from the Northwest Indian College.
