Hydrocarbon source apportionment for the 1996 Paso del Norte Ozone Study

The 1996 Paso del Norte (PdN) ozone study as conducted to improve current u nderstanding of the significant meteorological and air quality processes th at lead to high concentrations of ozone in El Paso, Texas (USA) and Ciudad Juarez, Chihuahua (Mexico). Two-hour canister samples were collected five t imes daily at 05.00-07.00 h, 07.00-09.00 h, 09.00-11.00 h, 11.00-13.00 h, a nd 15.00-17.00 h MST during intensive study periods at one urban and one ru ral site on each side of the border. An automated gas chromatograph was ope rated at one site in central El Paso. Source profiles (the fractional chemi cal composition of emissions) from motor vehicles, gasoline, liquefied petr oleum gas. and commercial natural gas were combined with source profiles fr om other studies for input to the Chemical Mass Balance (CMB) receptor mode l to apportion the measured non-methane hydrocarbons (NMHC) to sources. On- road vehicle emissions accounted for one-half to two-thirds of the NMHC in Ciudad Juarez and El Paso with the highest contributions occurring during t he morning and afternoon commute periods. Emissions from diesel exhaust con tributed approximately 2-3% of NMHC in Ciudad Juarez and less than 2% in El Paso. The average sum of liquid gasoline and gasoline vapor increased duri ng the day in Ciudad Juarez from 2% at 06.00 h to approximately 12% at 16.0 0 h. Diurnal and day-of-the-week patterns in the liquid gasoline contributi ons are essentially identical to the corresponding patterns for motor vehic le exhaust, which suggest that a large fraction of the liquid gasoline cont ribution may be associated with tailpipe emissions rather than evaporative emissions from motor vehicles or industrial sources. Including the sum of t he two sources put the upper limit for tailpipe contributions at 60-70% of NMHC. (C) 2001 Elsevier Science B.V. All rights reserved.