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SUMMERTIME AMBIENT FORMALDEHYDE IN FIVE U.S. METROPOLITAN AREAS: NASHVILLE, ATLANTA, HOUSTON, PHILADELPHIA, TAMPA
DASGUPTA, P. K., J. LI, G. ZHANG, W. T. LUKE, W. A. MCCLENNY, J. STUTZ, AND A. FREID. SUMMERTIME AMBIENT FORMALDEHYDE IN FIVE U.S. METROPOLITAN AREAS: NASHVILLE, ATLANTA, HOUSTON, PHILADELPHIA, TAMPA. ENVIRONMENTAL SCIENCE AND TECHNOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 39(13):4767-4783, (2005).
1. Provide the Agency with semi-continuous and real-time instrumentation for its monitoring of ozone, ozone precursors, and reaction products of ozone formation.
2. Provide the Agency with semi-continuous and real-time instrumentation for its monitoring of water-soluble PM components and water-soluble atmospheric gases.
In this paper, we briefly review the atmospheric chemistry and previous intercomparison measurements for HCHO, with special reference to the diffusion scrubber-Hantzsch reaction based fluorescence instrument used in the field studies reported herein. Then we discuss summertime HCHO levels in 5 major US cities measured over 1999-2002, primarily from ground-based measurements. Land-sea breeze circulations play a major role in observed concentrations in coastal cities. Very high HCHO peak mixing ratios were observed in Houston (>47 ppb) where the overall median mixing ratio was 3.3 ppb, the corresponding values in Atlanta were ~>18 and 7.9 ppb, respectively. The peak and median mixing ratios (9.3 and 2.3 ppb) were the lowest for Tampa, where the land-sea breeze also played an important role. In several cities, replicate HCHO measurements were made by direct spectroscopic instruments; the instruments were located kilometers from each other and addressed very different heights (e.g.,106 m vs. 10 m). Even under these conditions, there was remarkable qualitative and often quantitative agreement between the different instruments, when they were all sampling the same airmass within a short period of each other. Local chemistry dominates how HCHO is formed and dissipated. The high concentrations in Houston unequivocally resulted from emissions near the ship channel; the same formaldehyde plume was measured at two sites and clearly ranged over tens of km. Local micrometeorology is another factor. HCHO patterns measured at a high rise site in downtown Nashville were very much in synchrony with other ground sites 12 km away until July 4 celebrations whence nighttime HCHO concentrations at the downtown site remained elevated for several days. The formation and dissipation of HCHO in the different cities are discussed in terms of other concurrently measured species and meteorological vectors. The vertical profiles of HCHO in and around Tampa under several different atmospheric conditions are presented. The extensive data set represented in this paper underscores that urban formaldehyde measurements can now be made easily; the agreement between disparate instruments (that are independently calibrated or rely on the absolute absorption cross section) further indicates that such measurements can be done reliably and accurately for this very important atmospheric species. The data set presented here can be used as a benchmark for future measurements if the use of formaldehyde precursors such as methanol or methyl tert-butyl ether (MTBE) as oxygenated fuel additives increase in the future.