Development of compact continuous measurement system for atmospheric carbonyl sulfide concentration

Abstract. Carbonyl sulfide (COS), the most abundant sulfur-containing gas in the atmosphere, is a source of stratospheric sulfate aerosol (SSA) and is used as a tracer for gross primary production (GPP). However, tropospheric COS sources and sinks entail great uncertainty due to the limited number COS observation sites. Thus, field measurements of COS concentrations worldwide are necessary to estimate the contribution of SSA and the global scale of GPP. Recently, MIRA Pico, a portable continuous COS concentration analyzer using mid-infrared absorption, has been released. MIRA Pico has a lower cost and is smaller than conventional laser COS analyzers. We modified and tested the MIRA Pico for atmospheric COS concentration measurements. The modified MIRA Pico exhibited ± 7.9 picomol (pmol) mol−1 (1σ) for a 15-min average, and calibration gas consumption was as low as no more than 3 L d−1. We also used the modified MIRA Pico for observations at Tsukuba, Japan. The observed COS concentrations ranged from 425 to 604 pmol mol−1, averaging a standard deviation (1σ) of (505 ± 33) pmol mol−1. The observed values agree with previous observations and exhibit clear diurnal variations. Furthermore, we installed the modified MIRA Pico in a passenger car to observe the COS concentration distribution in Tsukuba City.