Methane and volatile organic compound emissions in New South Wales

[摘要] In order to investigate and better understand atmospheric methane (CH4) emission sources, particularly from the coal seam gas industry, the NSWEPA commissioned CSIRO Energy to undertake a study to develop methods for characterising CH4 and other gaseous emissions from different area sources in NSW. While there are internationally recognised methods for estimating (rather than measuring) CH4 and other greenhouse gas emissions from many sectors of the economy for national inventory reporting, some ofthese methods do not provide sufficient accuracy for baseline monitoring in sensitive areas. Hence, methods for directly measuring emissions at the facility level are necessary for assessing the impacts of certain activities on greenhouse gas emissions, and assessing the effectiveness of mitigation measures.The specific aims of the project were to firstly develop and trial methods that can be used to locate, identify and quantify CH4 emissions from the CSG industry in particular but also other industries such as wastewater treatment, municipal solid waste disposal, coal mining, agriculture and natural sources. Secondly,investigations were undertaken to examine the possibility of attributing sources by measuring the chemical composition of the emissions and isotopic ratios of carbon and hydrogen in CH4 and carbon in carbon dioxide (CO2). Finally, ambient concentrations of volatile organic compounds were measured at various sites to gain an understanding of source related impacts on ambient air quality and to identify the prevalence of compounds that may specifically characterise a source.Measurements were made between June 2014 and May 2016 at 16 sites across NSW that included:- coal seam gas operations,- landfills,- wastewater treatment plants,- agriculture (a rice farm and cattle feedlot),- coal mining and- natural sources.In addition to the on site measurements, ambient CH4 concentration was measured across NSW throughout the course of the project.Methane EmissionsA variety of methods for detecting and quantifying CH4 emissions were examined. Mobile surveys using a cavity ringdown spectrometer mounted in a 4WD vehicle was effective at locating CH4 sources even while being driven at highway speeds. More than 25,000 km of surveys were driven during the project and a widevariety of CH4 sources were detected. The surveys indicated that CH4 concentrations across the state are generally consistent with normal background levels expected in continental locations, with somewhat higher concentrations in urban areas compared to rural regions. There was also often variation in ambient concentrations due to atmospheric mixing conditions - higher concentrations were often observed during the early morning. However, there were many locations in both rural and urban areas where significantly elevated CH4 concentrations were detected. In some cases, the source of the CH4 could be identified (e.g. landfills, agriculture, coal mining etc.); however in other instances, the source of the elevated CH4concentrations was not apparent. Some of the unidentified sources were located in urban centres where there was no obvious source of CH4; it is hypothesised that some of these sources may be due natural gas reticulation emissions. Further work is required to confirm this.Several methods for quantifying CH4 emission rates were examined. Continuous techniques which include eddy covariance or inverse methods can provide temporal information on emissions over extended periods but they require fixed monitoring installations and because of the number of sites where measurements were required for this project, these techniques were not considered to be feasible. Instead, periodic measurements were made at most sites at least four times (often many more times) using ground level plume traversing and surface flux chamber methods. Later in the project, a tracer gas method was also applied at a number of sites.The plume traversing method ha...

[发布机构] CSIRO

[学科分类] 地球科学(综合)