HR: 12:05h
AN: A42B-07    [Abstracts]
TI: Airborne Formaldehyde and Formic Acid Measurements Using a Pulsed QC Laser During NEAQS/ITCT 2004
AU: * Herndon, S
EM: herndon@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Rd., Billerica, MA 01821 United States
AU: Nelson, D
EM: ddn@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Rd., Billerica, MA 01821 United States
AU: Shorter, J
EM: shorter@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Rd., Billerica, MA 01821 United States
AU: Jim\'{e}nez, R
EM: jimenez@fas.harvard.edu
AF: Harvard University Department of Earth and Planetary Science, 29 Oxford St., Cambridge, MA 02138 United States
AU: Zahniser, M
EM: mz@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Rd., Billerica, MA 01821 United States
AB: We present our quantum cascade laser (QCL) measurements of atmospheric formaldehyde (HCHO) and formic acid (HCOOH) performed on the NOAA P3 aircraft as part of the New England Air Quality Study / Intercontinental Transport and Chemical Transformation project in July-August 2004. Formaldehyde is a key species for studies of photochemical oxidation pathways in the troposphere. Formaldehyde is made throughout the troposphere via photo-initiated oxidation of methane and other hydrocarbons. It is also directly emitted by urban combustion sources including jet aircraft engines, cold-start automobiles, compressed natural gas buses, and other gasoline vehicles without a functioning oxidation catalyst. In the remote troposphere, formaldehyde is a photolytic source of HOx. Secondary organic aerosol mass loading can be attributed to the oxidation of precursor VOCs and HCHO is a valuable indicator of photochemical activity in an aging air mass. The capability to perform airborne formaldehyde measurements in the troposphere is a valuable tool and these measurements can help further our understanding of several atmospheric processes. We detect formaldehyde using Tunable Infrared Laser Differential Absorption Spectroscopy (TILDAS). TILDAS provides sensitive, specific detection with a rapid time response (1 s) that makes it especially suitable for airborne measurements. The recent availability of quantum cascade lasers has led to smaller, more compact TILDAS instruments than has been previously possible using lead-salt tunable diode lasers (TDLs). QCLs operate near-room temperature in pulsed mode which greatly simplifies the deployment logistics for aircraft operation. QCLs have superior spectral mode stability which minimizes operator interaction during flight deployments and offers greater potential for automated operation. In July and August of 2004, we deployed a quantum cascade laser system aboard NOAA's P3 aircraft as part of the New England Air Quality Study (NEAQS). This was our initial experience measuring HCHO and HCOOH. Tropospheric concentrations of HCHO were measured in flight with three different lasers at frequencies 1765, 1774 and 1783 cm$^{-1}$. Each of these wavelength regions allowed a simultaneous measurement of formic acid. This campaign represented the first flight-based measurement of any species using a pulsed quantum cascade laser for mid IR absorption spectroscopy. The aircraft instrument used a heated PTFE inlet system and a formaldehyde-free zero air generator based on the design of the NCAR TDL HCHO system to obtain background spectra. Though the detection method itself is based on an absolute Beer's Law absorption technique, a permeation source of HCHO was added near the top of the sample inlet to characterize inlet effects and provide additional confidence in the measured concentration. We will present measurement results from the campaign including formaldehyde and formic acid profiles measured during transects of forest fire and power plant plumes as well as mapping of the New York City urban outflow plume. We will also present the results of inter-comparisons with other airborne formaldehyde instruments and the relationship of our measurements to those of other atmospheric species (including acetic acid and acetaldehyde).
DE: 0317 Chemical kinetic and photochemical properties
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting