Potential for City Parks to Reduce Exposure to Hazardous Air Pollutants

Abstract

Benzene, toluene, ethylbenzene, and xylenes (BTEX) are hazardous air pollutants commonly found in outdoor air. Several studies have explored the potential of vegetation to mitigate BTEX in outdoor air, but they are limited to a northern temperate climate and present conflicting results. To investigate this issue in a subtropical climate, we deployed passive air samplers for two weeks in parks and nearby residences at four locations: three in an urban area and one in a rural area in Alabama, USA. All BTEX concentrations were below health-based guidelines and were comparable to those found in several other studies in populated settings. Concentrations of TEX, but not benzene, were 3-39% lower in parks than at nearby residences, and the differences were significant. In and around two of the parks, toluene:benzene ratios fell outside the range expected for vehicular emissions (p<0.01), suggesting that there are additional, industrial sources of benzene near these two locations. The ratio of m-,p-xylene:ethylbenzene was high at all locations except one residential area, indicating that BTEX were freshly emitted. Concentrations of individual BTEX compounds were highly correlated with each other in most cases, except for locations that may be impacted by nearby industrial sources of benzene. Results of this study suggest that parks can help reduce BTEX exposure by a modest amount, but future research is needed to ascertain this potential through more measurements at higher spatial and temporal resolution and analysis of vegetation for evidence of uptake of BTEX.