Comparison of Arctic and Antarctic trace gas column abundances from ground-based Fourier transform infrared spectrometry

Column abundances of several atmospheric trace gases have been derived from solar absorption spectra measured from McMurdo, Antarctica (77.9 degrees S, 166.7 degrees E), in September and October 1986 and from solar and lunar absorption spectra recorded in Ny Alesund, Spitsbergen (78.9 degrees N, 11.9 degrees E), during winter and spring 1992-1995. The same analysis software, including the molecular spectroscopic parameters and initial volume mixing ratio profile shapes, was employed for both data sets to minimize the possibility of introducing systematic biases. The results clearly show that denitrification in the Antarctic lower stratosphere results in much smaller column abundances of HNO3 than in the Arctic. The springtime recovery of HCl in the Antarctic showed a stronger increase than in the Arctic. The ClONO2 peak occurred about 1 month later in the Antarctic and was found to be less pronounced than in the Arctic. After accounting for the 30% increase in total chlorine between 1986 and 1993, the minimum values for HCl + ClONO2 are similar in the Arctic and the Antarctic, indicating that both polar regions show nearly the same activation of chlorine during the polar night. However, in the Arctic the low values of HCl + ClONO2 start to recover in February, whereas in the Antarctic the lack of NO2, caused by the denitrification, delays the increase of HCl + ClONO2 by about 1 month. A simple one-dimensional model was able to reproduce the behavior of HCl and ClONO2, simply by assuming a one month later date for the last Antarctic polar stratospheric clouds together with greater latitude excursions of the Arctic air parcel trajectories. The model runs imply that in the Antarctic the reconversion of ClONO2 to HCl occurs about 1 month later than in the Arctic. Furthermore, the results imply that any differences in the O-3 depletion are caused mainly by differences in the stratospheric temperatures and dynamics and only to a small extent by the increased chlorine loading. The total column abundances of the short-lived tropospheric trace gases C2H6, C2H2, CO, and CH2O are found to be up to 10 times higher in the Arctic compared with the Antarctic, reflecting the hemispheric imbalance in production.