In both cases, large uncertainties remain. Sometimes they are due to methodological differences or different estimations for the value of a statistical life. The 2012 meta-study by Burtraw et al. ( As far as air pollution is concerned, power sources can largely be split into two groups: i) carbon-based electricity sources, including fossil fuels and biomass, with coal-fired plants causing damages that are considerably higher than those from natural gas, oil, or biomass; ii) sources that have impacts on air pollution from low-carbon electricity sources - nuclear, wind, solar, hydro, geothermal and tidal - are either negligible or zero, although some indirect emissions could arise during production.