Handbook of Solvents - George Wypych - ChemTech - Ventech!

17.4 Organic solvent impacts on tropospheric air pollution 1199
regulatory focus is now turning from VOCs towards NOx, the other main precursor to
ozone. Another imminent regulatory issue is the control of ambient fine particulate matter.
While the role of solvent emissions in forming particulate matter is not well understood,
studies to date do not suggest they are a major contributor.
17.4.5 SUMMARY
Solvents are, and will continue to be, one of the major classes of organic compounds emitted
into the atmosphere. These compounds have a wide range of air quality impacts. Accumulation
of toxic compounds indoors is of concern, although outdoors the concern of
toxicity is significantly less substantial due to rapid dilution. In the stratosphere, some of the
halogenated solvents lead to depletion of the protective layer of ozone, while in the troposphere
solvents generally lead to increased ozone levels, where it adversely affects health
and the environment. The former has led to regulations of CFCs, and the latter to regulations
of organic solvents. Some solvents are also considered to be precursors to the formation of
secondary tropospheric pollutants other than ozone, such as particulate matter, however
these relationships are currently less certain.
In the aggregate, total VOC emissions from solvents in the U.S. are the second largest single
source category in polluted urban areas, falling just behind motor vehicle VOC emissions
both in terms of mass and urban ozone production. For now, regulations are designed to reduce
the loss of ozone in the stratosphere and the formation of excess ozone in the troposphere.
However, while some solvents are very reactive, others are substantially less
reactive, suggesting that there is considerable opportunity to reduce urban ozone formation
from solvents by utilizing substitutes with low ozone forming potentials. Currently, most
regulations are targeted at reducing the mass of VOC emissions, not their relative impacts
on ozone.
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