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Description:
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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 . |