A Closer Look at Air Pollution in Houston: - Green Houston

and vulnerable subgroups. Substances were designated“Possible Risks” when there was partial or limited evidencethat suggested they might constitute a significant risk undercertain circumstances, and “Probable Risks” when therewas substantial corroborating evidence that they were likely torepresent a significant risk under the right conditions. Thosesubstances for which there was compelling and convincing evidenceof significant risk to the general population or vulnerablesubgroups at current ambient concentrations were labeled“Definite Risks.”As shown in Table 1, 12 air pollutants were classified as“Definite Risks”. The Task Force found that existing and projectedambient concentrations of two criteria pollutants - ozoneand fine particles (PM 2.5) - are almost certainly causing respiratoryand cardiopulmonary effects in some individuals as wellas contributing to premature death. It was also determined thatairborne concentrations of seven carcinogens - diesel particulatematter (see Appendix 4 for more detail on this pollutant),1,3-butadiene, chromium VI (see Appendix 4 for more detailon this pollutant), benzene, ethylene dibromide, formaldehyde,and acrylonitrile - pose an unacceptable increased cancer risk.In addition, it was concluded that five substances -- 1,3-butadience(reproductive effects in addition to being a carcinogen),formaldehyde (respiratory effects), acrolein (respiratoryeffects), chlorine (respiratory effects), hexamethylene diisocyanate(pulmonary and respiratory effects). -- are present atambient concentrations that represent an unacceptableincreased risk for chronic disease in Houston.The evidence is not as strong but nevertheless persuasivethat an additional 9 air pollutants are likely to pose unacceptablehealth risks at concentrations measured or modeledin Houston air. These substances were designated as“Probable Risks,” and included eight carcinogens - vinyl chloride,acetaldehyde, ethylene dichloride, naphthalene, arseniccompounds, carbon tetrachloride, ethylene oxide, 1,1,2,2-tetrachloroethane- and one pollutant - acrylic acid - that has chronicnon-cancer effects. These are shown in Table 2 on pg. 14.13