Point source emissions of trace gases such as NO₂, SO₂, and HCHO play an important role in the budgets of various gaseous pollutants and particulate matter in urban atmospheres. Consequently, their accurate monitoring is crucial for a better understanding of the composition and chemistry of the boundary layer, as well as their impact on air quality. Emissions of SO₂ from marine vessels have moved into the focus of atmospheric research and air quality agencies in recent years, due to their impact on particulates in coastal regions.  It has also been proposed recently that flares in petrochemical facilities can directly emit HCHO and SO₂ and thus contribute to the levels of these compounds in urban areas, such as Houston. In both cases accurate measurements are sparse due to a lack of techniques that allow remote sensing fence-line observations.

For the 2009 FLAIR/SHARP project in Houston, TX, we developed an Imaging Differential Optical Absorption Spectrometer (I-DOAS) to visualize and quantify point source emissions of HCHO and SO₂ from various sources. The instrument was deployed at different facilities and in the Texas City Industrial Complex and the Houston Ship Channel to provide a unique view at the emissions from flares and smoke stacks, as well as the exhaust of ships. Formaldehyde was clearly identified in burning flares, while unlit flares appear not to emit this compound. We also clearly observed the emission of SO₂ in some flares and marine vessels. In this presentation we will describe the design of the portable I-DOAS instrument and discuss the results from our observations in Houston.