Long-term tropospheric formaldehyde concentrations deduced from ground-based fourier transform solar infrared measurements

摘要

We report a 13-year (1992–2005) dataset of total column measurements offormaldehyde (HCHO) over Lauder, New Zealand, inferred from solar infraredspectra measured using a high-resolution Fourier Transform Spectrometer(FTS). Ambient HCHO concentrations at this rural location are often close tolevels typical of remote marine environments (250 ppt), which are closeto the detection limit using standard techniques. Consequently we develop anew method that successfully produces HCHO columns with sufficientsensitivity throughout the whole season. HCHO columns over Lauder have astrong seasonal cycle (±50%), with a mean column of 4.9×10 molecules cm,peaking during summer months. A simple box model ofCH oxidation reproduces the observed broad-scale seasonal cycle, butsignificantly underestimates the seasonal peak HCHO ground concentrationsduring summer. This suggests the existence of an additional significantsource of HCHO, possibly isoprene that cannot be explained by oxidation ofCH alone. The ground-based FTS column data compare well withcollocated HCHO column measurements from the Global Ozone MonitoringExperiment (GOME) satellite instrument during the operational period of GOME(1996–2001, =0.65, mean bias=10%, =48).