Methane emission to the atmosphere from landfills in the Canary Islands
Authors: Padrón Eleazar , Asensio-Ramos María , Pérez Nemesio M. , Di Nardo Daniel , Albertos-Blanchard Violeta T. , Alonso Mar , Tassi Franco , Raco Brunella , López Dina 
Published: March 2020

&lt;p&gt;Methane (CH&lt;sub&gt;4&lt;/sub&gt;) is an important greenhouse gas, and is increasing in the atmosphere by 0.6% (10 ppb) each year. Important sources of this gas are landfills; in fact more than 10% of the total anthropogenic emissions of CH&lt;sub&gt;4&lt;/sub&gt; are originated in them by anaerobic degradation of organic matter. Even after years of being closed, a significant amount of landfill gas can be released to the atmosphere through its surface as diffuse or fugitive degassing.&lt;/p&gt;&lt;p&gt;Many landfills currently report their CH&lt;sub&gt;4&lt;/sub&gt; emissions to the atmosphere using model-based methods, which are based on the rate of production of CH&lt;sub&gt;4&lt;/sub&gt;, the oxidation rate of CH&lt;sub&gt;4&lt;/sub&gt; and the amount of CH&lt;sub&gt;4&lt;/sub&gt; recovered (Bingemer and Crutzen, 1987). This approach often involves large uncertainties due to inaccuracies of input data and many assumptions in the estimation. In fact, the estimated CH&lt;sub&gt;4&lt;/sub&gt; emissions from landfills in the Canary Islands published by the Spanish National Emission and Pollutant Sources Registration (PRTR-Spain) seem to be overestimated due to the use of protocols and analytical methodologies based on mathematical models. For this reason, direct measurements to estimate CH&lt;sub&gt;4&lt;/sub&gt; emissions in landfills are essential to reduce this uncertainty.&lt;/p&gt;&lt;p&gt;In order to estimate the CH&lt;sub&gt;4&lt;/sub&gt; emissions to the atmosphere from landfills in the Canary Islands, 34 surveys have been performed since 1999 to the present. Each survey implies hundreds of CO&lt;sub&gt;2 &lt;/sub&gt;and CH&lt;sub&gt;4&lt;/sub&gt; efflux measurements covering the landfill surface area. Surface landfill CO&lt;sub&gt;2&lt;/sub&gt; efflux measurements were carried out at each sampling site by means of a portable non-dispersive infrared spectrophotometer (NDIR) model LICOR Li800 following the accumulation chamber method. Samples of landfill gases were taken in the gas accumulated in the chamber and CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; were analyzed using a double channel VARIAN 4900 micro-GC. The CH&lt;sub&gt;4&lt;/sub&gt; efflux measurement was computed combining CO&lt;sub&gt;2&lt;/sub&gt; efflux and CH&lt;sub&gt;4&lt;/sub&gt;/CO&lt;sub&gt;2&lt;/sub&gt; ratio. To quantify the diffuse or fugitive CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; emission, gas efflux contour maps were constructed using sequential Gaussian simulation (sGs) as interpolation method. Considering that (a) there are 6 controlled landfills in the Canary Islands, (b) the average area of the 34 studied cells is 0.15 km&lt;sup&gt;2&lt;/sup&gt; and (c) the mean value of the CH&lt;sub&gt;4&lt;/sub&gt; emission estimated for the studied cells range between 6.2 and 7.2 kt km&lt;sup&gt;-2&lt;/sup&gt; y&lt;sup&gt;-1&lt;/sup&gt;, the estimated CH&lt;sub&gt;4&lt;/sub&gt; emission to the atmosphere from landfills in the Canary Islands showed a range of 5.7-6.7 kt y&lt;sup&gt;-1&lt;/sup&gt; (mean value of 6.2 kt y&lt;sup&gt;-1&lt;/sup&gt;). On the contrary, and for the same period of time, the PRTR-Spain estimates the CH&lt;sub&gt;4&lt;/sub&gt; emission in the order of 6.4-16.4 kt y&lt;sup&gt;-1&lt;/sup&gt; (mean value of 9.2 kt y&lt;sup&gt;-1&lt;/sup&gt;), nearly 46% more than our estimated value. This result demonstrates the need to perform direct measurements to estimate the surface fugitive emission of CH&lt;sub&gt;4&lt;/sub&gt; from landfills.&lt;/p&gt;&lt;p&gt;&lt;em&gt;Bingemer, H. G., and P. J. Crutzen (1987), J. Geophys. Res. 92, 2182-2187.&lt;/em&gt;&lt;/p&gt;