Atmospheric chemistry of ethane and ethylene

Abstract

A detailed study of ethane and ethylene photochemistry is presented for the troposphere and stratosphere. It is demonstrated that the loss of ethane is controlled by OH in the troposphere and Cl in the stratosphere. Observations of ethane show a stratospheric behavior indicative of a free chlorine concentration below 30 km that is only 10% of the predicted value given by both our photochemical model calculations and those done by others. The inferred lower amount of chlorine cannot be explained by heterogeneous processes for concentrations of aerosols representing average background conditions, nor does current stratospheric photochemistry show agreement. Chemical destruction of ethane and ethylene within the atmosphere leads to the production of carbon monoxide, formaldehyde, and other products. Tropospheric concentrations of formaldehyde are enhanced by nearly a factor of 3 for an ethylene mixing ratio of 2 ppb. Simultaneous monitoring of formaldehyde and carbon monoxide, as well as other products, will greatly aid in determining the relative importance of different tropospheric CO sources. Peroxyacetyl nitrate (PAN) acts as a reservoir for odd‐nitrogen at the expense of HNO3, HO2NO2, NO, and NO2.

Global distributions of C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>2</sub>, HCN, and PAN retrieved from MIPAS reduced spectral resolution measurements

“…Xiao et al, 2008) estimate industrial activity as dominating, former ones (Rudolph, 1995) propose equality between both sources. Dominating sinks are reaction with OH in the troposphere and with atomic chlorine (Cl) in the stratosphere (Aikin et al, 1982). Mixing ratios of C 2 H 6 measured by MIPAS close to the tropopause often reach values of 400 pptv, and up to 1.2 ppbv at highly polluted air masses at single measurements.…”

Carbon monoxide (CO) and ethane (C<sub>2</sub>H<sub>6</sub>) trends from ground-based solar FTIR measurements at six European stations, comparison and sensitivity analysis with the EMEP model

“…The ethyl radical is then transformed through a complicated pattern of oxidations and reductions and ultimately ends up as CO (Aikin et al, 1982).…”

Large-scale upper tropospheric pollution observed by MIPAS HCN and C<sub>2</sub>H<sub>6</sub> global distributions

“…The tropospheric lifetime of C 2 H 6 has been estimated at a few months by Rudolph and Ehhalt (1981) and at 2 months by Hough (1991). The main tropospheric loss process is reaction with OH, whereas the major stratospheric sink is reaction with Cl (Aikin et al, 1982).…”