Signatures of terminal alkene oxidation in airborne formaldehyde measurements during TexAQS 2000

Abstract

[1] Airborne formaldehyde (CH 2 O) measurements were made by tunable diode laser absorption spectroscopy (TDLAS) at high time resolution (1 and 10 s) and precision (±400 and ±120 parts per trillion by volume (pptv) (2s), respectively) during the Texas Air Quality Study (TexAQS) 2000. Measurement accuracy was corroborated by in-flight calibrations and zeros and by overflight comparison with a ground-based differential optical absorption spectroscopy (DOAS) system. Throughout the campaign, the highest levels of CH 2 O precursors and volatile organic compound (VOC) reactivity were measured in petrochemical plumes. Correspondingly, CH 2 O and ozone production was greatly enhanced in petrochemical plumes compared with plumes dominated by power plant and mobile source emissions. The photochemistry of several isolated petrochemical facility plumes was accurately modeled using three nonmethane hydrocarbons (NMHCs) (ethene (C 2 H 4 ), propene (C 3 H 6 ) (both anthropogenic), and isoprene (C 5 H 8 ) (biogenic)) and was in accord with standard hydroxyl radical (OH)-initiated chemistry. Measurement-inferred facility emissions of ethene and propene were far larger than reported by inventories. Substantial direct CH 2 O emissions were not detected from petrochemical facilities. The rapid production of CH 2 O and ozone observed in a highly polluted plume (30+ parts per billion by volume (ppbv) CH 2 O and 200+ ppbv ozone) originating over Houston was well replicated by a model employing only two NMHCs, ethene and propene.

Design and performance of a tunable diode laser absorption spectrometer for airborne formaldehyde measurements

“…[31] During the Texas Air Quality Study 2000 (TexAQS 2000) mission, overflights of the La Porte airport (Houston, Texas) were made in order to compare multiple airborne and ground measurements, including the NCAR TDLAS (airborne) and UCLA DOAS (ground) instruments [Wert et al, 2003]. The validity of these overflight comparisons was supported by the excellent agreement between aircraft and ground ozone measurements, as well as by good mixing determined from the multiple DOAS paths.…”

“…At equal methanol and CH 2 O concentrations this interference is +3.8%. Average methanol errors associated with the polluted boundary layer are typically less than +15% (methanol/CH 2 O < 4): see below and Wert et al [2003]. Higher average methanol/CH 2 O ratios are found in the background and free troposphere, producing typical methanol interferences of +10 to 40% [Fried et al, 2003a[Fried et al, , 2003b.…”

“…Where applicable, the present system will be contrasted with previous systems, to illuminate factors that have produced this improved performance. In an effort to provide a comprehensive assessment of instrument performance, some supporting material that was published previously is summarized here [Fried et al, 1997a[Fried et al, , 1997b[Fried et al, , 2003aWert et al, 1996Wert et al, , 2002Wert et al, , 2003]. …”

“…In many cases the important CH 2 O precursors also contribute substantially to total atmospheric hydroxyl radical (OH) hydrocarbon reactivity. As a result, measurements of CH 2 O provide a valuable check of photochemical model predictions concerning recent hydrocarbon oxidation [Liu et al, 1992;Lee et al, 1998;Fried et al, 2002Fried et al, , 2003aWert et al, 2003]. In addition, CH 2 O measurements are important to the calculation of accurate OH concentration fields and odd hydrogen (HO x ) budgets [Ayers et al, 1997;Fried et al, 1997a;Wennberg et al, 1998;Jaeglé et al, 2000].…”

“…Only a small number of VOCs are both abundant and efficient CH 2 O producers, however. These important CH 2 O precursors are methane in the background atmosphere [Finlayson-Pitts and Pitts, 1986;Heikes, 1992;Greenberg et al, 1992], and the terminal alkenes in polluted regimes [Dodge, 1990;Lee et al, 1998;Goldan et al, 2000;Wert et al, 2003]. In many cases the important CH 2 O precursors also contribute substantially to total atmospheric hydroxyl radical (OH) hydrocarbon reactivity.…”