Stratospheric Odd Nitrogen: Measurements of HNO3, NO and O3 near 54°N in Winter

Data obtained during three stratospheric measurement campaigns from Cold Lake, Alberta (100.0°W, 54.4°N), in February 1977, 1978, and 1979 are presented. Altitude profiles of NO, HNO3, O3, CFM‐11, CFM‐12, and N2O and ground‐based total column measurements of NO2 were obtained and are compared with similar measurements made at 51°N in summer. The winter data demonstrate enhanced variability when compared with summer conditions, but in general in winter (1) there is a greater abundance of HNO3 and the stratospheric layer is thicker, (2) there is less nitric oxide particularly in the 18‐ to 28‐km region and the vertical distributions are characterized by strong mixing ratio gradients, and (3) the column abundance of NO2 is lower and exhibits a diurnal change qualitatively similar to that observed in summer. The difference between the summer and winter observations is not solely due to changes in photochemistry but requires consideration of stratospheric dynamics. We correlate the reduction in NO x in winter with the production of N2O5 in regions of little or no insolation followed by transport to Cold Lake. The unusual profiles are shown to result from air masses at different altitudes having either different origins, for example, polar or mid‐latitude, or different transit times from the source to the sampling point.