Airborne and ground based measurements of volatile organic compounds using proton transfer reaction mass spectrometry in Texas and Mexico City

Measurements of ambient volatile organic compounds (VOCs) by proton transfer reaction mass spectrometry (PTR-MS) are reported from recent airborne and surface based field campaigns. The Southeast Texas Tetroon Study (SETTS) was a project within the TEXAQS 2005 field campaign, conducting airborne measurements that investigated the nocturnal Lagrangian transport of industrial plumes downwind of the Houston, Texas metropolitan area. On the evening of July 26-27, a polluted air mass with elevated mass 43, mass 45 and mass 57 VOCs along with elevated O3, CO, and NOx was tracked from the Houston metropolitan area to an area northwest of Shreveport, LA, a distance of over 200 miles. This campaign demonstrated that the PTRMS is capable of tracking a VOC plume over large distances and these measurements indicate that transport of VOCs, particularly light alkenes and their oxidation products, out of the Houston metropolitan area may need to be considered by areas downwind of the Houston area when they are determining how to attain their air quality goals. During the MILAGRO field campaign in March 2006 VOCs were measured by PTR-MS instrumentation on a rooftop in the urban mixed residential and industrial area north northeast of downtown Mexico City. Diurnal profiles of weekday and weekend/holiday aromatic VOC concentrations clearly show the influence of vehicular traffic during the morning rush hour time period and during the afternoon hours although a separate late afternoon peak is not seen. Plumes of toluene elevated as much as 216 parts per billion by volume (ppbv) and ethyl acetate elevated as much as 183 ppbv above background levels were observed during the late night and early morning hours. These plumes indicate the probability of significant industrial sources of these two compounds in the region. The high levels of toluene measured by our PTR-MS exceed levels that would be predicted by examination of the Mexico City Metropolitan Area (MCMA) emission inventory and when these VOC measurements are integrated with measurements conducted throughout the MCMA a better understanding of both the overall spatial pattern of VOCs in the MCMA as well as its variability will be attained.