Oxalic Acid and Oxalate in the Atmosphere
Oxalic acid gas concentrations were measured at a number of locations in Australia and Malaysia using passive samplers. The Australian locations range from remote areas such as Mount Isa, Qld and the Burrup Peninsula, WA to rural in the Hunter Valley, NSW and urban Melbourne. Malaysian sites include the urban area of Kuala Lumpur and a rural area in the Cameron Highlands north of Kuala Lumpur.
Concentrations of oxalic acid gas at the remote and rural sites range from about 0.2 ppb to 1.2 ppb with a very strong annual cycle with high concentrations during the summer periods. At the urban site at Petaling Jaya concentrations of oxalic acid were higher than the remote sites, ranging from about 1 ppb to 5 ppb and up to about 15 ppb during episodic events, with no distinct annual cycle.
The only clearly defined source of oxalic acid is motor vehicle exhaust. However, the data presented here show a widespread occurrence of oxalic acid gas in the atmosphere which probably cannot be accounted for by emissions from motor vehicles. The seasonal variation in this data exhibit a summer maximum and a winter minimum suggesting that plants may be the dominant source of oxalic acid in remote and rural atmospheres. In addition, the data from Petaling Jaya show that concentrations of oxalic acid were high during periods of intense forest fires in Asia. This indicates that biomass burning may also be a significant source of oxalic acid gas concentrations in the atmosphere.