Free tropospheric CO, C2H6, and HCN above central Europe: Recent measurements from the Jungfraujoch station including the detection of elevated columns during 1998

Time series of free tropospheric carbon monoxide (CO), ethane (C2H6), and h ydrogen cyanide (HCN) column abundances have been derived from observations at the International Scientific Station of the Jungfraujoch (ISSJ) at 3.58 -km altitude in the Swiss Alps (latitude 46.55 degreesN, 7.98 degreesE long itude). The free troposphere was assumed to extend from 3.58 to 11 km altit ude, and the related columns were derived for all three molecules from high spectral resolution infrared solar spectra recorded between January 1995 a nd October 1999. The three molecules show distinct seasonal cycles with max ima during winter for CO and C2H6, and during spring for HCN. These seasona l changes are superimposed on interannual variations. The tropospheric colu mns of all three molecules were elevated during 1998. Increases were most p ronounced for HCN with enhanced values throughout the year, up to a factor of 2 in January 1998 when compared to averages of the other years. The incr eased tropospheric columns coincide with the period of widespread wildfires during the strong El Nino warm phase of 1997-1998. The emission enhancemen ts above ISSJ are less pronounced, and they peaked after the increases meas ured above Mauna Loa (19.55 degreesN, 155.6 degreesW). Tropospheric trends for CO, C2H6, and HCN of (2.40 +/- 0.49), (0.47 +/- 0.64), and (7.00 +/- 1. 61)% yr(-1)(1 sigma) were derived for January 1995 to October 1999. However , if 1998 measurements are excluded from the fit, CO and HCN trends that ar e not statistically significant, and a statistically significant decrease i n the C2H6 tropospheric column, are inferred. Comparisons of the infrared C O columns with CO in situ surface measurements suggest that the CO free tro pospheric vertical Volume mixing ratio profile generally decreases with alt itude throughout the year.