Dual Max-DOAS measurements of area averaged formaldehyde fluxes in Texas City, TX

Formation of ozone and particulates in the urban atmosphere is driven by OH radical chemistry. An accurate quantitative description of the sources of OH/HO₂ radical precursors, including HCHO and HONO is thus essential for a quantitative understanding of air quality in urban areas. Recent observations and modeling activities for the Houston area have suggested that direct emission of HCHO from industrial facilities may contribute to the HCHO budget, and thus indirectly impact the OH/HO₂ budget. Despite their potential importance, little is known about the HCHO emissions from various types of industrial facilities due to a lack of available observational techniques.

Here we present a novel approach to measure area averaged trace gas emissions using two Multi-Axis Differential Optical Absorption Spectrometers placed upwind and downwind of potential pollutant sources. Both instruments use opto-mechanical scanners to measure the total number of trace gas molecules in a cross-wind “slice”. By subtracting the upwind from the downwind observations and using wind speed and direction, fluxes of pollutant in question can be calculated directly.

During the 2009 SHARP/FLAIR experiment this method was employed for the first time in Texas City, TX, with a focus on formaldehyde. MAX-DOAS instruments from our respective laboratories sampled the atmosphere in East-West oriented vertical slices upwind and downwind from the Texas City Industrial Complex. Both instruments successfully observed “slice-integrated” HCHO levels during a 3 week period from April 22 to May 14, 2009. In this presentation, we will show the results of our study in Texas City. The potential of this new method for future applications will also be discussed.