Proposal to add compounds to exclusion list of volatile organic compound definition: chapter 4

4.0 Science

• 4.1 VOC Classification
• 4.2 Impacts on Human Health or the Environment

4.1 VOC Classification

VOCs are those compounds of carbon¹⁹ that are volatile. Operationally, this is defined as those organic compounds that have a vapour pressure greater than 10-1 Torr at 25°C and 760 mm Hg. Many VOCs contribute to air pollution by forming ground-level ozone through atmospheric photochemical reactions. However, different VOCs have different levels of reactivity; therefore they do not react at the same speed or contribute to ozone formation to the same extent.

It has been the U.S. EPA's policy that organic compounds with a negligible level of reactivity need not be regulated to reduce ozone. In determining negligible reactivity, the U.S. EPA compares the reactivity of a compound to the reactivity levels of ethane-using methods, which are based on the reaction rate constant of hydroxyl radical (known as K_OH) in the air, and on the maximum incremental reactivity (MIR), expressed either on a reactivity per gram basis or on a reactivity per mole basis (for technical information, see Appendix I). Compounds with reactivity levels less than or equal to the reactivity levels of ethane may be deemed negligibly reactive, and are excluded from the regulatory definition of VOC.

Environment Canada is in agreement with this evaluation for determining reactivity levels for VOCs.

4.2 Impacts on Human Health or the Environment

It is important to note that these compounds were only evaluated for their contributions to the formation of ground-level ozone. Excluding these compounds from the VOC listing on Schedule 1 of CEPA 1999 does not preclude their future management for other reasons, such as climate change or their inherent toxicity to human health or the environment.

¹⁹ Excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate.