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Development and Application of a Real Time Optical Sensor for Atmospheric Formaldehyde
EPA Grant Number: R828598C731Title: Development and Application of a Real Time Optical Sensor for Atmospheric Formaldehyde
Investigators: Fraser, Matthew P. , Tittel, Frank K.
Institution: Rice University
EPA Project Officer: Krishnan, Bala S.
Project Period: September 1, 1999 through August 31, 2002
Project Amount: $86,476
RFA: Gulf Coast Hazardous Substance Research Center (Lamar University) (1996)
Research Category: Targeted Research , Hazardous Waste/Remediation
Description:
The ambient air quality measures currently being performed are inadequate to elucidate the atmospheric chemistry of atmospheric volatile organic compounds (VOCs) or to assess the contributions from different sources to individual concentrations of these compounds. The objective of this proposal is to develop and evaluate a novel, compact and robust sensor for real-time measurements of ambient formaldehyde. Currently, the most widely used formaldehyde quantification technique relies on chemically sorbing formaldehyde in large volumes of air followed by extraction and chemical analysis. Optical methods developed to date rely on cryogenic laser cooling, and are not portable.
Formaldehyde is critically important to the chemistry of the urban atmosphere. During daylight, formaldehyde photolyzes and decomposes to release the free radicals that drive photochemical ozone formation. With atmospheric lifetimes of a few hours, formaldehyde is expected to be an important contributor to the radical formation that leads to the high concentrations of ozone observed in Houston.
Objective:Building upon previous efforts, a new technique for real-time measurements of ambient formaldehyde concentrations will be developed to allow a more accurate, instantaneous measurements of ambient formaldehyde levels. Previous efforts have lead to the development of a compact tunable mid-infrared spectroscopic instrument capable of rapid and accurate measurements of formaldehyde [1]. However, the current detection limits of this instrument for formaldehyde of 30 ppbv prevent ambient concentrations of formaldehyde to be quantified (formaldehyde concentrations are typically 5-10 ppbv in urban atmospheres) [2]. The proposed work will improve detection limits for the current optical gas sensor based on a nonlinear optical frequency conversion process known as difference frequency generation (DFG) [3] to the I ppbv level. The proposed sensor will employ quasi-phase matched periodically poled lithium niobate (PPLN) pumped by diode lasers and/or fiber lasers to produce tunable infrared radiation at wavelengths near 3.5pm, which spans several strong rotational-vibrational absorption lines of formaldehyde. The proposed infrared laser sources take advantage of recent significant developments of new infrared nonlinear materials, progress in near-infrared III-V diode and solid state lasers, fiber optics technology, and ultra low noise Peltier cooled infrared detectors [3]. The cost of the instrument components and operating costs (including calibration) will be compared to the costs of the methods currently used in routine air quality monitoring.
Approach:An analysis of the historical ozone data in Houston suggests that many summertime ozone episodes originate at the Ship Channel [4], and the instrument developed will be deployed to quantify ambient concentrations of formaldehyde in the Houston Ship Channel during the summertime photochemical smog season (May-September). In addition to real-time measurements, simultaneous quantifications of formaldehyde using traditional, well-characterized methods will be performed over 2 and 4 hour time averages for comparison between instantaneous measurements of formaldehyde and time-integrated measurement techniques [2]. The instantaneous measurements will allow single air parcels to be analyzed to determine if photochemical generation exceeds photochemical destruction of formaldehyde. This result will be compared to predictions of the formaldehyde chemistry predicted by air quality models. Additionally, maps of formaldehyde concentrations will be prepared using mobile monitoring, and used to differentiate directly emitted formaldehyde from formaldehyde generated by photochemical oxidation of other volatile organic compounds. The short-averaging time measurements from the optical detector will allow the evaluation of the rapid formaldehyde chemistry that is important in ground-level ozone formation by multiple measurements in individual air parcels as they pass the monitoring location.
Expected Results:The proposed work will develop a novel technique for the ambient quantification of urban air pollutant concentrations, provide important real-time data on ambient formaldehyde concentrations in Houston, allow the validation of current air quality models, and determine the regional flux of formaldehyde by using boundary crosswind integrated concentrations. The real-time concentration measurements will lead to a better understanding of the chemistry and ultimate fate of formaldehyde in the Houston atmosphere.
Publications and Presentations:Publications have been submitted on this project: View all 10 publications for this project
Journal Articles:Journal Articles have been submitted on this project: View all 2 journal articles for this project
Supplemental Keywords:Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Air, Scientific Discipline, RFA, Air Pollutants, Chemicals, Atmospheric Sciences, Environmental Engineering, Environmental Chemistry, Monitoring/Modeling, aerosols, Formaldehyde, Volatile Organic Compounds (VOCs), real-time monitoring, environmental monitoring, optical detection, atmospheric chemistry, atmospheric measurements, optical sensor
Progress and Final Reports:
Final Report