Small-scale spatial variability of particulate matter < 10 μm (PM10) and nitrogen dioxide

Epidemiological studies often rely only on data from a single monitoring station at a study site. However, significant small-scale spatial gradients for air pollutants are inevitable and one monitoring station cannot be representative for the entire population living in the study region. Small-scale spatial gradients (horizontally and vertically) of particulate matter < 10 micro-meter (PM10) and NO2 were examined along a roadside in Zurich during the winter and summer seasons (1994-1995). Horizontal and vertical concentration gradients for PM10 were about 13% (spatial coefficient of variation), and for NO2 about 15%. For PM10, the effect of season on the horizontal and vertical gradient was small. For NO2, the small-scale spatial gradients were highly influenced by season: during the spring-summer season, spatial gradients were much greater than during the autumn-winter season. This implies that future monitoring programmes, should include more monitoring sites for PM10 and, especially for NO2, the spring-summer season should include far more spatial resolution.