Related by context. Frequent words. (Click for all words.) 73 air pollution 72 particulate matter 68 ozone 63 smog 63 particulates 60 nitrogen oxide 60 pollutants 59 particulate 59 nitrogen oxides 59 pollutant 57 soot 57 diesel exhaust 57 pollution 56 mercury emissions 55 NOx 55 emissions 54 mercury pollution 54 sulfur dioxide 53 Carbon monoxide 52 carbon monoxide 52 Air Quality 52 carbon dioxide emissions 51 secondhand smoke 51 greenhouse gases 51 emission 50 mercury 50 Smog 49 greenhouse gas emissions 49 Emissions 49 respiratory illnesses 48 greenhouse emissions 48 volatile organic compounds 48 GHG emissions 48 Clean Air 47 respiratory ailments 47 greenhouse gasses 47 exhaust emissions 47 Pollution 47 radon 47 VOCs 47 tailpipe emissions 46 greenhouse gas 46 Air Pollution Control 46 hydrogen sulfide 46 Environmental Protection Agency 45 asthma 45 micrograms 45 wood stoves 45 carcinogens 45 carcinogen 44 toxic chemicals 44 COPD 44 lung diseases 44 CO2 emissions 44 ash 44 carbon dioxide 44 greenhouse gas emission 44 EPA 44 dioxins 44 carbon dioxide CO2 43 carbon emissions 43 benzene 43 emission reductions 43 perchlorate 43 cigarette smoke 43 asthmatics 43 ppb 43 heat trapping gases 42 Ozone 42 acid rain 42 Asthma 42 salt intake 41 respiratory diseases 41 lung disease 41 passive smoking 41 Lung Association 41 burning fossil fuels 41 methane 41 carbon emission 41 disease COPD 41 Environmental Quality 41 PFOA 41 emission reduction 41 nitrates 41 radioactive iodine 41 arsenic 40 relative humidity 40 algae blooms 40 PAH 40 reduce carbon emissions 40 toxins 40 respiratory illness 40 nonsmokers 40 gases 40 lung function 40 exhaust fumes 40 phosphorus 40 concentrations 40 dioxin 40 atmospheric carbon dioxide 39 CO2