Measurements of C₂‐C₆ hydrocarbons during the Polar Sunrise1992 Experiment: Evidence for Cl atom and Br atom chemistry

Abstract

Grab samples for nonmethane hydrocarbons (NMHCs) were collected from three sites: daily at Alert, Northwest Territories (82.5° N, 62.3° W) from January 21 to April 19, daily at an ice floe 150 km north of Alert from April 9 to 25, and on an aerial survey conducted in April over the Arctic archipelago. Insitu measurements of n‐butane and i‐pentane were also made hourly at Alert from April 2 to April 15. During the dark period (January to March), C2‐C6 hydrocarbon concentrations correlated with those of methane. Concentrations declined gradually from January to April, consistent with removal by HO radicals. On the other hand, during low‐ozone periods in April an additional decrease in NMHC concentrations and change in distribution were observed. Concentration changes of alkanes were correlated to Cl atom reaction rate constants. Acetylene displayed a greater change in concentration than predicted from chlorine kinetics, possibly indicating additional removal by Br atoms. The Br atom concentration derived from the depletion of acetylene can account for the low‐ozone concentrations periodically observed at Alert. The estimated Cl atom concentration is too small to be a significant loss mechanism for ozone. Thus the data from Alert and the ice floe site provide evidence for Cl and Br atom chemistry during the ozone depletion episodes observed at polar sunrise.

Reactions at surfaces in the atmosphere: integration of experiments and theory as necessary (but not necessarily sufficient) for predicting the physical chemistry of aerosols

“…4 shows the measured ratio of i-butane to n-butane as a function of the ratio of i-butane to propane for the pure NaNO 3 case. As discussed by Jobson et al, 170 the two butane isomers should decay at approximately the same rate if they are being removed by reaction with OH (solid line in Fig. 4).…”

Bromine activation in the troposphere by the dark reaction of O3 with seawater ice

“…However, Tang and McConnell (1996) have proposed that it might still be sufficient if it activates chain reactions involving bromide from sea salt particles accumulated on the snow pack during polar winter. Chlorine atom chemistry has also been observed simultaneously with the ozone depletion episodes (Jobson et al, 1994), supporting sea salt as the bromine source. Consistent with this, Hopper et al (1998) observed that the ozone depleting processes occurred only in air masses above sea ice.…”

Spatial and temporal variability of nonmethane hydrocarbon mixing ratios and their relation to photochemical lifetime

“…A final data set is taken from the Polar Sunrise Experiment 1992 field campaign at Alert, N.W.T., during the "dark" period from January to March [Jobson et al, 1994].…”