Atmospheric Formaldehyde Monitoring in the Greater Houston Area in 2002

Abstract

A laser spectrometer based on difference frequency generation (DFG) was deployed for real-time long-term monitoring of HCHO concentrations at an environmental monitoring site located at Deer Park, Texas, in the Greater Houston area. Three HCHO concentration measurements were made during the periods of July 20-31 (period I), August 2-14 (period II), and August 24-September 25 (period III), 2002. In periods I and II, differences in HCHO concentrations are apparent between day and night measurements, with elevated concentrations during daylight hours. Most of the HCHO peak values are less than 20 ppbV except for two intense peaks on August 02 (approximately 25 ppbV) and August 04 (approximately 30 ppbV). The formaldehyde concentration levels in ambient air at the measurement site are produced mainly by the photochemical oxidation of volatile organic compounds (VOCs) caused by intense sunlight during periods I and II. This observation was made based on a comparison with the ozone concentration, solar radiation, temperature, relative humidity, and wind speed data obtained from the Texas Commission on Environmental Quality (TCEQ). During period III, data collected by a time-integrating wet-chemical technique are compared to the data collected by the spectroscopic instrument.

Radical precursors and related species from traffic as observed and modeled at an urban highway junction

“…Although HCHO may be produced through reactions of alkenes with OH, it can also be formed from ozonolysis of terminal olefins or 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). These latter processes represent net OH sources.…”

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

“…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.…”

Ppb-level mid-infrared ethane detection based on three measurement schemes using a 3.34-μm continuous-wave interband cascade laser

“…WMS requires a tunable laser capable of single-frequency emission and a narrow linewidth at the targeted absorption line of a gas molecule. To meet this requirement, several laser sources are commercially available, e.g., difference-frequency generation (DFG) [21] and optical parameter oscillators (OPO) [22]. In recent years, quantum cascade lasers (QCLs) [23] in the 4-to 12-µm spectral range and interband cascade lasers (ICLs) in the 3-to 6-µm range, capable of operating with low electrical power consumption [24], provide continuous-wave (CW) output power levels of >5 mW.…”