Measurements of Volatile Organic Compounds Using Proton Transfer Reaction – Mass Spectrometry during the MILAGRO 2006 Campaign

E C Fortner,M André,W Berk Knighton,P Sheehy,R M Volkamer,J Zheng,L Molina,R Zhang

doi:10.5194/acp-9-467-2009

Abstract

Abstract. Volatile organic compounds (VOCs) were measured by proton transfer reaction – mass spectrometry (PTR-MS) on a rooftop in the urban mixed residential and industrial area North Northeast of downtown Mexico City as part of the Megacity Initiative – Local and Global Research Observations (MILAGRO) 2006 field campaign. Thirty eight individual masses were monitored during the campaign and many species were quantified including methanol, acetaldehyde, toluene, the sum of C2 benzenes, the sum of C3 benzenes, acetone, isoprene, benzene, and ethyl acetate. The VOC measurements were analyzed to gain a better understanding of the type of VOCs present in the MCMA, their diurnal patterns, and their origins. Diurnal profiles of weekday and weekend/holiday aromatic VOC concentrations showed the influence of vehicular traffic during the morning rush hours and during the afternoon hours. Plumes including elevated toluene as high as 216 parts per billion (ppb) and ethyl acetate as high as 183 ppb were frequently observed during the late night and early morning hours, indicating the possibility of significant industrial sources of the two compounds in the region. Wind fields during those peak episodes revealed no specific direction for the majority of the toluene plumes but the ethyl acetate plumes arrived at the site when winds were from the Southwest or West. The PTR-MS measurements combined with other VOC measuring techniques at the field site as well as VOC measurements conducted in other areas of the Mexico City Metropolitan Area (MCMA) will help to develop a better understanding of the spatial pattern of VOCs and its variability in the MCMA.

Highlights

Mexico City Metropolitan Area (MCMA) is the location of some of the most severe air pollution in the world
A large number of ambient Volatile organic compounds (VOCs) concentrations were measured by a proton transfer reaction – mass spectrometer (PTR-MS) instrument on a rooftop in the urban mixed residential and industrial area North Northeast of downtown Mexico City as part of the MILAGRO 2006 campaign, with the purpose to gain a better understanding of the type of VOC species present in the particular area of the MCMA
The primary objective of this paper is to present the general characteristic of VOCs at T0 site during the campaign

Summary

Introduction

Mexico City Metropolitan Area (MCMA) is the location of some of the most severe air pollution in the world. Mexico City is located in the tropics at a high elevation, further enhancing photochemical activity and ozone production Another factor contributing to the air pollution problem in this area is that the city lies in a valley surrounded by mountains and thermal inversions are common during the morning hours. Activities in the city lead to the emission of volatile organic compounds (VOCs) which react with nitrogen oxides (NO + NO2 = NOx) emitted primarily through combustion sources. This interaction leads to production of O3, secondary organic aerosols, and other toxic chemicals through photochemical processes (Tie et al, 2001; Zhang et al, 2003; Lei et al, 2004). During the late 1980s and early 1990s, the Mexican one-hour air quality standard of 110 parts per billion (ppb) of O3 has been violated in approximately 80% of the days annually and the maximum O3 values of over 300 ppb have been recorded (INE, 2000)

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