Handbook of Solvents - George Wypych - ChemTech - Ventech!

17.4 Organic solvent impacts on tropospheric air pollution 1195
from non-local sources as compared to that of VOCs, coupled with the usual absence of
strong local NOx sources and the presence of natural VOC sources. In such rural environments,
the formation of ozone is limited more by the absence emissions of NOx, and most
ozone present was directly transported from upwind. Indeed, in most of the troposphere,
except in areas of strong NOx sources, the availability of NOx governs ozone production.
17.4.3.3 Assessing solvent impacts on ozone and VOC reactivity
As mentioned previously, the contribution of solvents to the VOC levels, and hence ozone
formation, is significant. For example, in Los Angeles, about 25% of the VOC mass is from
solvent use. 1 This fraction is down from earlier years due to various controls such as using
water-based paints and enclosing/controlling paint spraying operations. On the other hand,
reduction in the use of CFCs as propellants has led to an increase in organic emissions from
substituted compounds. 2 However, the impact on ozone formation by a specific source is
not directly proportional to the amount of VOC emitted by that source. A major determinant
of the ozone forming potential is the reactivity of the compound or compound mixture emitted.
Reactivity can be viewed as the propensity for a compound to form ozone, and this propensity
varies dramatically between compounds and between environments. 18,19
As seen in Table 17.4.1, ‘box’ model (single cell) simulations designed to represent
summertime conditions in Los Angeles, California indicate that the amount of carbon associated
with each class of compound only roughly corresponds to the amount of ozone
formed from those compounds. Methane, which reacts very slowly but comprises most of
the carbon, contributes little to ozone formation. Alkenes and aromatics are only a small
part of the total carbon, but lead to much of the ozone formation.
Table 17.4.1. Percentage of ozone production attributable to each organic. The
percentages shown should be viewed as only approximate, and will depend upon
local emissions characteristics. (*While not considered organic carbon, carbon
monoxide acts to facilitate ozone formation similar to organic compounds.) [Adapted
from F.M. Bowman and J.H. Seinfeld, J. Geophys. Res., 99, 5309, (1994) and M.S.
Bergin et al., Env. Sci. Technol., 29, 3029 (1998)]
Compound Class
Percent of carbon in each
specified class
Percent of ozone due to
specified organic class
carbon monoxide* 35 6
methane 40 1
aldehydes and ketones 1 3
non-methane alkanes, ~4C 8 17
non-methane alkanes, ~8C 5 16
aromatics, including toluene 3 5
aromatics, including xylenes
and others
3 13
ethene 2 12
biogenic alkenes ans isoprene 1 10
other alkenes 2 17