A hunt for elusive trace gases in the marine boundary layer

We present a feasibility study into the use of solar remote sensing Fourier transform infrared spectrometry (FTS) to detect elusive trace gases in the marine boundary layer. The study acquired spectra from Wollongong, Australia (34.5°S, 150°E, 30m above sea level) at dawn as the sun rose over the ocean. We hoped to detect elusive atmospheric trace gases such as hypochlorous acid (HOCl) and dinitrogen pentoxide (N2O5) in these spectra, since the geometry results in path-lengths through the marine boundary layer in excess of 100km at dawn. Spectra were successfully collected at SZA greater than 90° above the marine horizon on four days due to the effects of diffraction in the atmosphere. Enhanced absorption features were observed for a large number of species and a spectral region for the possible observation of hypochlorous acid was identified. The experimental setup allowed for transmission of some infrared radiation but not enough to generate a sufficient signal to noise ratio for meaningful retrievals of total column amounts. Almost all absorption features were either saturated or had low signal to noise. Despite these problems, FTS has potential and some simple changes to the experimental setup could prove this to be a useful method.