Summary of comments and responses: addition of precursors to particulate matter, chapter 5

5. Scientific foundation

Comment received

Inaccuracies in the statistical software used to estimate health risks from particulate matter (PM) and ozone have led to incorrect information for short-term epidemiological studies. More factual information is needed before the government proceeds with regulations or toxicity declarations for these substances.


The scientific evidence indicating that air pollution is a public health problem is still valid. While the numbers may have changed, the existence of a cause and effect relationship between air pollution and premature death remains unquestioned. The Governmen's confidence in the association between the precursors, the formation of PM10 and ozone and their health effects remains as it was stated in the science assessment documents.

Comment received

A better understanding is needed of regional contributions of the precursors to PM and ozone and the individual substances in ambient air that are causing health effects.


The federal government recognizes that PM10 and ozone formation is complex and varies under different conditions and in different parts of the country; however, this does not refute the conclusion that the precursors participate in chemical reactions that result in the formation of PM10 and ozone, which are toxic. Risk assessments are not intended to identify options for control or priorities. Rather, such issues are relevant to the risk management stage and will be considered when identifying priorities for action and developing specific risk management tools to reduce emissions of the precursors, PM10 and ozone. Risk management tools will be developed through a consultative approach with stakeholders.

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