Related by context. Frequent words. (Click for all words.) 71 air pollution 62 pollutants 61 pollution 60 smog 60 nitrogen oxide 59 ozone pollution 58 particle pollution 58 particulate matter 57 nitrogen oxides 57 pollutant 55 carbon dioxide emissions 55 diesel exhaust 55 nitrogen oxide emissions 54 emissions 54 mercury pollution 53 particulates 53 tailpipe emissions 53 sulfur dioxide 53 greenhouse gases 53 sulfur dioxide emissions 52 soot 52 mercury emissions 52 greenhouse gas emissions 51 emission 51 CO2 emissions 50 nitrogen dioxide 50 ozone 50 greenhouse gasses 49 greenhouse gas 49 Environmental Protection Agency 49 exhaust emissions 49 greenhouse emissions 49 heat trapping gases 48 greenhouse gas GHG emissions 48 polluters 48 carbon emissions 48 carbon dioxide CO2 emissions 47 GHGs 47 polluting 47 NOx 47 Emissions 46 burning fossil fuels 46 toxic chemicals 46 Clean Air 46 Air Pollution 46 GHG emissions 46 particulate 46 asthma sufferers 45 volatile organic compounds 45 cleaner burning 45 greenhouse gas emission 45 Pollution 45 carbon dioxide 45 global warming gases 45 smokestacks 44 Lung Association 44 CO2 emission 44 EPA 44 toxics 44 polluter 44 carcinogens 43 reduce carbon emissions 43 VOCs 43 emission reductions 43 coal fired 43 Air Quality 43 diesel engines 42 cleaner fuels 42 toxins 42 smoggy 42 polluted 42 acid rain 42 benzene 41 Carbon monoxide 41 hexavalent chromium 41 reducing carbon emissions 41 emitters 41 emission reduction 41 sulfur coal 41 reducing CO2 emissions 41 toxic substances 41 mercury 41 emitting 41 tailpipe 41 CO2 41 Air Pollution Control 41 secondhand smoke 40 phosphorus 40 carbon dioxide CO2 40 carbon emission 40 Superfund sites 40 gases 40 hazardous substances 40 airborne particles 40 emitted 40 diesel powered 40 hazardous chemicals 40 respiratory illnesses 39 harmful chemicals 39 exhaust fumes 39 carbon monoxide