20th century trends and budget implications of chloroform and related tri-and dihalomethanes inferred from firn air

Abstract

Abstract. Four trihalomethane (THM; CHCl 3 , CHBrCl 2 , CHBr 2 Cl and CHBr 3 ) and two dihalomethane (DHM; CH 2 BrCl and CH 2 Br 2 ) trace gases have been measured in air extracted from polar firn collected at the North Greenland Icecore Project (NGRIP) site. CHCl 3 was also measured in firn air from Devon Island (DI), Canada, Dronning Maud Land (DML), Antarctica and Dome Concordia (Dome C), Antarctica. All of these species are believed to be almost entirely of natural origin except for CHCl 3 where anthropogenic sources have been reported to contribute ∼10% to the global burden. A 2-D atmospheric model was run for CHCl 3 using reported emission estimates to produce historical atmospheric trends at the firn sites, which were then input into a firn diffusion model to produce concentration depth profiles that were compared against the measurements. The anthropogenic emissions were modified in order to give the best model fit to the firn data at NGRIP, Dome C and DML. As a result, the contribution of CHCl 3 from anthropogenic sources, mainly from pulp and paper manufacture, to the total chloroform budget appears to have been considerably underestimated and was likely to have been close to ∼50% at the maximum in atmospheric CHCl 3 concentrations around 1990, declining to ∼29% at the beginning of the 21st century. We also show that the atmospheric burden of the brominated THM's in the Northern Hemisphere have increased over the 20th century while CH 2 Br 2 has remained constant over time implying that it is entirely of natural origin.

A growing threat to the ozone layer from short-lived anthropogenic chlorocarbons

“…Like CH 2 ClCH 2 Cl, C 2 Cl 4 is almost exclusively anthropogenic in origin, used primarily as a solvent in the dry-cleaning industry, as a metal degreasing agent, and as a chemical intermediate, for example in the manufacture of the hydrofluorocarbons HFC-134a and HFC-125. CHCl 3 is believed to be largely natural in origin (seawater, soils, macroalgae), but potential anthropogenic sources include the pulp and paper industry, water treatment facilities, and HFC production (McCulloch, 2003;Worton et al, 2006;Montzka et al, 2011).…”

Halogenated organic species over the tropical South American rainforest

“…Global average mixing ratios of 18.5 pmol mol −1 between 1985 and 1995 (Khalil and Rasmussen, 1999) decreased to average background levels of 8.9 (±0.1) pmol mol −1 in the years 1994(O'Doherty et al, 2001). However, a recent model study suggests that a higher anthropogenic contribution (41-50% of the global sources) before 1990, versus 25-29% in 2001, would explain the global observations better (Worton et al, 2006).…”

Formation mechanisms of trichloromethyl-containing compounds in the terrestrial environment: A critical review

“…O 3 depletion, partitioning of HO x and NO x , the oxidation of volatile organic compounds, reduction in the life time of methane) (Saiz-Lopez and Glasow, 2012). Trichloromethane is one example of a halogenated compound with mainly natural origin and with the terrestrial environment as a major source (Keene et al, 1999;Worton et al, 2006).…”