Summertime Ambient Formaldehyde in Five U.S. Metropolitan Areas:  Nashville, Atlanta, Houston, Philadelphia, and Tampa

Abstract

First, 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 five major U.S. 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 approximately >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 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 air mass within a short period of each other. Local chemistry dominates how HCHO is formed and dissipated. The high concentrations in Houston resulted from emissions near the ship channel; the same formaldehyde plume was measured at two sites and clearly ranged over tens of kilometers. 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 HCHO concentrations at the downtown site remained elevated for several days and nights. 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 HCHO 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 increases in the future.

Formaldehyde and its relation to CO, PAN, and SO<sub>2</sub> in the Houston-Galveston airshed

“…Relatively stable at night, HCHO rapidly photolyzes after sunrise and serves as an important source for early morning radicals. Some of the highest HCHO levels in North America have been reported for the HGA, in particular the HSC area, ranging from ∼35 to 52 ppbv (Dasgupta et al, 2005;Eom et al, 2008). Airborne HCHO measurements in HGA likewise exceeded 30 ppbv on some occasions; terminal olefins were identified as the most important precursors .…”

“…It is likely that thus a shallow layer existed between the boundary height and the height where the wind shear occurred, which predominantly contained air masses which have passed the HSC area before arriving the Moody Tower area. There have been indications for stratified SO 2 plumes aloft based on early morning ozone sonde launchings (Rappenglück et al, 2008), others have previously observed simultaneously elevated SO 2 and HCHO at HSC (Dasgupta et al, 2005) tial Optical Absorption Spectroscopy (DOAS) at the Moody Tower for 14 September 2009. They report elevated SO 2 mixing ratios along the upper light path (130-300 m a.g.l.)…”

“…Interestingly, highest HCHO mixing ratios were detected aloft, approximately between 300-1100 m. In the HSC, HCHO events, e.g. short-term increases of HCHO mixing ratios up to 15 ppbv during nighttime, have been reported to coincide with SO 2 and H 2 O 2 excursions, suggesting that HRVOCs may be co-emitted with SO 2 from specific sources and lead to rapid production of peroxy radicals (Dasgupta et al, 2005). The same study also reported nighttime excursions of HCHO, possibly from flare combustion (the events were accompanied by NO peaks); primary HCHO is thus likely present in at least some industrial emissions.…”

“…While HCHO may be emitted primarily from incomplete combustion in either mobile or stationary sources (Zweidinger et al, 1988;Altshuller, 1993;Chen et al, 2004;Dasgupta et al, 2005), it can also be formed from ozonolysis of terminal olefins, a pathway that does not consume OH. Relatively stable at night, HCHO rapidly photolyzes after sunrise and serves as an important source for early morning radicals.…”

Global upper-tropospheric formaldehyde: seasonal cycles observed by the ACE-FTS satellite instrument

“…In the continental boundary layer, HCHO concentrations of the order of a few parts per billion by volume (ppbv) are reported and can reach values greater than 10 ppbv in large cities (Dasgupta et al, 2005) and tropical regions (Kesselmeier et al, 2002). The HCHO concentration falls below 0.5 ppbv far from the sources in the oceanic background atmosphere for example (e.g., Heikes et al, 2001;, 2003aFrost et al, 2002).…”