Analysis of the air pollution climate at a central urban background site

摘要

Measurements of air pollutants from a background site in central London are analysed. These comprise hourly data for CO, NO, NO_2, O_3, SO-2 and PM_(10) from 1996 to 2008 and particle number count from 2001 to 2008. The data are analysed in terms of long-term trends, annual, weekly and diurnal cycles, and autocorrelation and cross-correlation functions. CO, NO and NO_2 show a typical traffic-associated pattern with two daily peaks and lesser concentrations at the weekend. Particle number count and PM_(10) show a similar cycle, but with smaller amplitude. Ozone has an annual cycle with a maximum in May, influenced by the spring maximum in background ozone, but the diurnal and weekly cycles are dominated by losses through reaction with nitric oxide. Particle number count shows a minimum corresponding with maximum air temperatures in August, whereas the CO, NO NO_2 and SO_2 show a minimum in June/July. There is a lower particle count to NO_x ratio at the background site compared to a central London kerbside site (Marylebone Road) and a seasonal pattern in particle count to NO_x and PM_(10) ratios consistent with loss of nanopartides by evaporation during atmospheric transport Sulphur dioxide peaks in the morning in summer, but at midday in winter consistent with emissions from elevated sources mixing down from aloft as the diurnal mixed layer deepens. Implications for epidemiological studies of air quality and health are discussed. Sulphur dioxide, carbon monoxide, nitric oxide and nitrogen dioxide show clear downward trends over the measurement period, PM_(10)declines initially before levels stabilised, and ozone concentrations increased.