Emission estimates of methyl chloride from industrial sources in China based on high frequency atmospheric observations

Abstract

Methyl Chloride (CH3Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion (Carpenter et al. 2014). In the global CH3Cl budget, the atmospheric CH3Cl emissions is predominantly maintained by natural sources, of which magnitudes have been relatively well-constrained. However, significant uncertainties still remain in the CH3Cl emission strengths from anthropogenic sources. High-frequency and high-precision in situ measurements of atmospheric CH3Cl concentrations obtained since 2008 at Gosan station (a remote background site in the East Asia) reveal significant pollution events superimposed on the seasonally varying regional background levels. Back trajectory statistics showed that air masses corresponding to the observed CH3Cl enhancement largely originated from regions of intensive industrial activities in China. Based on an inter-species correlation method, estimates of CH3Cl emissions from manufacturing industries including coal combustion, use of feedstocks, or process agents in chemical production for China (2008–2012) are 297 ± 71 Gg yr.−1 in 2008 to 480 ± 99 Gg yr.−1 in 2009, followed by a gradual decrease of about 25% between 2009 and 2012 (398 ± 92 Gg yr.−1 for 2010; 286 ± 68 Gg yr.−1 for 2011; 358 ± 92 Gg yr.−1 for 2012). The annual average of industrial CH3Cl emissions for 2008–2012 (363 ± 85 Gg yr.−1) in China is comparable to the known total global anthropogenic CH3Cl emissions accounting only for coal combustion and indoor biofuel use. This may suggest that unless emissions from the chemical industry are accounted for, global anthropogenic emissions of CH3Cl have been substantially underestimated. In particular, since industrial production and use of CH3Cl have not been regulated under the Montreal Protocol (MP) or its successor amendments, continuous monitoring of Chinese CH3Cl outflow is important to properly evaluate its anthropogenic emissions.