Methyl and ethyl nitrates belong to what is known as the "odd nitrogen" reservoir, a group of molecules that regulates the levels of tropospheric ozone in remote marine environments. The two compounds were believed to come from anthropogenic emissions. But the new research, conducted by Adele L. Chuck of the University of East Anglia in Norfolk, England and colleagues, suggest otherwise. The team tested air and surface seawater samples taken along two paths in the Atlantic Ocean and detected the presence of both methyl and ethyl nitrate in the seawater--far from human activity--with higher concentrations recorded closer to the equator. By comparing the concentrations of the compounds in the water and in the air directly overhead, the researchers calculated that equatorial surface waters were supersaturated with both methyl and ethyl nitrates--their concentrations were nearly 800 percent higher than what is normally expected under such temperature and pressure conditions. How these compounds arise remains unclear. "No mechanisms for the production of alkyl nitrates in aquatic systems, or indeed, in any biological system are known," the authors write. Indeed, as Karlheinz Ballschmiter of the University of Ulm in Germany notes in an accompanying editorial, it's surprising that "even for very simple compounds like methyl and ethyl nitrate, basic questions of their chemistry in the environment are still open."
Scientists have determined that some chemicals thought to be solely man-made are in fact made by Mother Nature, too. A report published today in the journal Science details the first direct evidence that methyl and ethyl nitrates, which are involved in ozone chemistry in the lower levels of the atmosphere, are produced naturally in the ocean.