Related by context. Frequent words. (Click for all words.) 83 nitrogen oxide 69 NOx 66 pollutants 66 sulfur dioxide 62 particulate matter 62 volatile organic compounds 62 carbon dioxide emissions 62 emissions 61 carbon dioxide 60 pollutant 60 greenhouse gases 60 sulfur dioxide emissions 60 air pollution 58 greenhouse gasses 58 ozone pollution 58 greenhouse gas 58 carbon dioxide CO2 58 particulates 58 exhaust emissions 57 mercury emissions 57 greenhouse gas emissions 57 tailpipe emissions 56 pollution 56 GHG emissions 56 emission 55 diesel exhaust 55 CO2 emissions 55 greenhouse emissions 55 CO2 54 ozone 54 VOCs 53 carbon emissions 53 nitrogen dioxide 53 Emissions 52 smog 52 global warming gases 51 heat trapping gases 51 emission reductions 50 mercury pollution 50 soot 50 greenhouse gas emission 49 burning fossil fuels 49 gasses 49 cleaner burning 49 flue gas 48 combustion 48 reduce carbon emissions 48 water vapor 48 Carbon dioxide 48 exhaust fumes 48 gases 48 particulate 47 Clean Air 47 ammonia 47 emission reduction 47 nitrogen 47 GHG 47 methane 47 carbon emission 46 acid rain 46 carcinogens 46 toxic chemicals 45 polluting 45 hydrogen 45 sulfur 45 coal fired 44 reducing carbon emissions 44 particle pollution 44 benzene 44 scrubbers 44 aerosols 44 emitted 42 oxides 42 biomass 42 toxins 42 mercury 42 diesel engines 42 harmful chemicals 42 phosphorus 42 syngas 42 hydrogen sulfide 42 carbon 42 cleaner fuels 42 Emission 42 organic compounds 42 Air Pollution 41 EPA 41 carbon monoxide 41 emit 41 tailpipe 41 zero emission 41 Carbon monoxide 41 VOC 40 combustion engine 40 regulate greenhouse gases 40 hazardous wastes 40 Ammonia 40 dioxins 40 Environmental Protection Agency 40 acrylamide 40 contaminants