Trends, interannual and seasonal variations of tropospheric CO, C2H6 and HCN columns measured from ground-based FTIR at Lauder and Arrival Heights
1National Institute of Water and Atmospheric Research, Lauder, New Zealand
2School of Chemistry, University of Wollongong, Wollongong, New South Wales, Australia
*now at: 1981 Omakau-Chatto Creek Road, Alexandra, New Zealand
Abstract. We analyse the carbon monoxide (CO), ethane (C2H6) and hydrogen cyanide (HCN) partial columns (from the ground to 12 km) derived from measurements by ground-based solar Fourier Transform Spectroscopy at Lauder, New Zealand (45° S, 170° E) and at Arrival Heights, Antarctica (78° S, 167° E) from 1997 to 2009. Significant negative trends are calculated for all species at both locations: CO (−0.90 ± 0.31% yr−1) and C2H6 (−3.10 ± 1.07% yr−1) at Arrival Heights and CO (−0.87 ± 0.30% yr−1), C2H6 (−2.70 ± 0.94% yr−1) and HCN (−0.93 ± 0.32% yr−1) at Lauder. The uncertainties reflect the 95% confidence limits. The dominant seasonal trends of CO and C2H6 at Lauder, and to a lesser degree at Arrival Heights, occur in austral spring when the correlations between CO and C2H6 and between CO and HCN maximize. Tropospheric columns of all three species are characterised by minima in March–June and maxima from August to November; this season is the southern-hemisphere tropical and sub-tropical biomass burning period. A tropospheric chemistry-climate model is used to simulate CO and C2H6 columns for the period of 1997–2009 using interannually varying biomass burning emissions; the model simulated tropospheric columns of CO and C2H6 compare well with the measured partial columns of both species. However, the model does not re-produce the significant negative trends of observed CO and C2H6 partial columns at both locations. Weak negative trends are calculated from model data. The model sensitivity calculations indicate that long-range transport of biomass burning emissions from Southern Africa and South America dominate the seasonal cycles of CO and C2H6 at both Lauder and Arrival Heights. Interannual variability of these compounds at both locations is largely triggered by variations in biomass burning emissions associated with large-scale El Nino Southern Oscillation and prolonged biomass burning events, e.g. the Australian bush fires.