This month, the U.S. EPA announced a very modest tightening of its ground-level ozone standards from 80 to 75 parts per billion, averaged over eight hours. This announcement met immediate criticism from public health advocates, since an extensive scientific review had recommended that the standard be lowered to between 60 and 70 parts per billion. EPA’s own risk estimate predicted hundreds more deaths and thousands more hospital visits each year, as a consequence of having the standard at 75 parts per billion instead of 70. Ground-level ozone is particularly hard on the vulnerable: children, the elderly, those with asthma, etc. In addition, recent research suggests that elevated ozone levels can severely restrict crop growth.
345 U.S. counties (including many major cities) already have air with more than 75 parts per billion of ozone. It’s not clear where the money or political will will come from to reduce those ozone levels. However, it’s against the law for the EPA to take cost into account when setting pollution standards, which are supposed to based only on health or science; it’s therefore hard to understand what health or science led them to select 75 ppb.
Ontario joined the chorus of criticism, calling the new EPA smog rules “too weak”. Southern Ontario cities regularly exceed the “Canada-Wide Standard” target for ozone of 65 parts per billion, (calculated as the three year average of the annual 4th highest daily maximum eight hour concentration), with “significant contributions” from pollution blowing in from the US. In total, 40% of Canadians live in areas with ozone levels higher than the Canada-Wide Standard. Ozone levels can be particularly high in the spring.
However, Ontario does not have an eight-hour limit for ozone. The current Reg. 346 standard for ozone is 200 parts per billion, averaged over a half hour; by 2020, Ontario will gradually tighten this to 155 parts per billion, averaged over one hour. US studies suggest that it is much harder to meet an eight hour target than it is to meet one hour targets.