Handbook of Solvents - George Wypych - ChemTech - Ventech!

1192 Michelle Bergin, Armistead Russell
Solvent compounds, especially CFCs and their replacements, participate in climate
change as “greenhouse gases”. Greenhouse gases allow short-wave solar radiation to pass
through, much of which the earth absorbs and re-radiates as long-wave radiation. Greenhouse
gases absorb the long-wave radiation, causing the atmosphere to heat up, thereby acting
as a blanket to trap radiation that would normally vent back to space. Climate change is a
controversial and complex issue, but it is likely that restrictions such as those from the
Kyoto Protocol will be adopted for emissions of compounds strongly suspected of exacerbating
climate change. Many countries have already adopted stringent policies to reduce
greenhouse gas emissions.
17.4.2.4 Urban and regional scales
Another area of concern regarding outdoor air is exposure to secondary pollutants that are
due, in part, to chemical reactions involving solvent compounds. Examples include the formation
of elevated levels of ozone, formaldehyde, organonitrates, and particulate matter.
Formaldehyde, a suspected carcinogen, is an oxidation product of organic compounds. Tropospheric
ozone and organonitrates, as discussed below, are formed from a series of reactions
of organic gases and nitrogen oxides in the presence of sunlight. Particulate matter
formation is linked to ozone, and some solvents may react to form particulate matter. The
particulate matter of concern is small (generally less than 2.5 μm in diameter) usually
formed by gas-to-aerosol condensation of compounds via atmospheric chemical reactions.
Ozone and particulate matter are both regulated as “criteria” pollutants in the United States
because they have been identified as risks to human health. Ozone is believed to cause respiratory
problems and trigger asthma attacks, and PM has a variety of suspected adverse
health outcomes (e.g., respiratory and coronary stress and failure). Many organonitrates,
such as peroxyacetyl nitrate, are eye irritants and phytotoxins. Currently, the formation and
effects of ozone are better understood than those of fine particulate matter and
organonitrates. The following section of this chapter discusses the effects, formation, and
control of tropospheric ozone. The role of solvents in forming particulate matter is currently
viewed as less urgent.
17.4.3 TROPOSPHERIC OZONE
Tropospheric ozone, a primary constituent of photochemical smog, is naturally present at
concentrations on the order of 20-40 parts per billion (ppb). 4 However, elevated levels of
ground-level ozone are now found virtually worldwide, reaching in some cities concentrations
of up to 10 times the natural background.
17.4.3.1 Effects
Ozone is believed to be responsible for both acute (short-term) and chronic (long-term) impacts
on human health, especially on lung functions. Major acute effects of ozone are decreased
lung function and increased susceptibility to respiratory problems such as asthma
attacks and pulmonary infection. Short-term exposure can also cause eye irritation, coughing,
and breathing discomfort. 5-7 Evidence of acute effects of ozone is believed to be “clear
and compelling”. 8 Chronic health effects may present a potentially far more serious problem;
however, definitive evidence is difficult to obtain. Recent studies do suggest that ambient
levels of ozone induce inflammation in human lungs, which is generally accepted as a
precursor to irreversible lung damage, 6 and chronic animal exposure studies at concentrations
within current ambient peak levels indicate progressive and persistent lung function
and structural abnormalities. 5,8