Figure 2.
Distributions of (a) CH4 and (b) N2O emission factors for composting reported in the literature and relative contribution to total GWP100 based on (c) mean values and (d) median values. The sample size (n) of data points contributing to each boxplot is indicated in the x-axis labels for parts (a) and (b); the first value refers to the sample size of CH4 emission factors, and the second value refers to that of N2O emission factors. Parts (a) and (b) have two y-axes: the left axis indicates the per-tonne mass of the specified pollutant emitted (exact values), and the right axis shows the CO2-equivalent emission factor (rounded values), so that CH4 and N2O emissions can be compared with respect to GWP100. The mean values for the boxplot data are indicated by the open point symbols, while outliers are shown as closed circles.