Continuous measurement of fine and ultrafine particulate matter, criteria pollutants and meteorological conditions in urban El Paso, Texas

Continuous measurements of aerosol size distributions were made in El Paso, TX, for a 21 day period in winter 1999. Size distribution measurements were performed at two urban locations in El Paso using two pairs of the scanning mobility particle sizer and the aerodynamic particle sizer. Complementary measurements also were performed for gas phase pollutants (CO, NO, NO2, O3) and meteorological conditions. Throughout the study, the mean ultrafine particle (those smaller than 0.1 μm in diameter) number concentration was 14,400 particles cm−3. There was a significant correlation between CO and both ultrafine and accumulation mode (those between 0.1 and 1 μm in diameter) particle count, with the Pearson correlation coefficient (r) values of 0.81 and 0.87, respectively. The correlation between NO and both ultrafine and accumulation mode particle count is also significant, but not as strong as the correlation of CO and the particle concentrations. Most pollutants were found to vary on diurnal cycles and to follow one of two different trends, either vehicular traffic schedules or sunlight intensity. Wind direction was found to have an influence not only on pollutant concentrations, but also on the correlation between pollutants. With southerly winds, CO, NO and NO2 concentrations were 25–140% greater than when the wind was coming from the north. Likewise, ultrafine and accumulation mode particle concentrations were approximately 100% greater for southerly than for northerly winds.