Meteorological influences on the vertical profile of nitrogen dioxide in a residential building near an expressway

Abstract

Studies are consistently reporting a link between mono-nitrogen oxides (NOx), particulate matter (PM) pollution and ill health. Motor vehicle emissions are considered to be the main source of NO2 and PM in ambient urban air of cities. The aim of this study is to assess the influence of an expressway and meteorological factors on the vertical profile of NO2 of a residential building in its vicinity. Measurements of NO2 and PM2.5 concentration, temperature, relative humidity and wind velocity and direction were obtained using Ogawa passive samplers, Grimm dust monitors, HOBO meters and Vaisala wind sensors, distributed evenly along the vertical profile of a naturally-ventilated residential building. The vertical profile measurement revealed a normal distribution trend between NO2 concentration and height, with the maximum NO2 concentration value occurring at the mid level. Both temperature and wind measurements individually showed positive correlation with NO2 level while relative humidity displayed a negative correlation. The relationship between these factors on NO2 level is considerably significant thus suggests that meteorological factors can exert influence on the NO2 concentration level. It was found that meteorological influence did bring about significant changes in the indoor-outdoor ratio of NO2 level. Both traffic volume and PM2.5 level were individually found to have a positive relationship with concentration of NO2. These findings have significant implications for planning of densely populated urban city, similar to that of Singapore and managing indoor air quality of buildings located in the close proximity of major roads and expressways.