Environmental Engineering Reference
In-Depth Information
With some exceptions, ambient toxic compounds in the Bay Area have been
reduced substantially. The introduction of reformulated fuels have been reduced
concentrations of benzene and 1,3-butadiene. MTBE has been eliminated from
gasoline. Perchloroethylene has been reduced dramatically because of BAAQMD
and CARB dry cleaner rules. Cleaner-burning diesel engines and cleaner diesel
fuel have reduced diesel concentrations over 50%. Carbon tetrachloride is one
exception, showing essentially no change. This pollutant is no longer manufactured
but is long-lived in the atmosphere and ubiquitous world-wide. A second exception
is chloroform, which has shown a 16% increase since the late 1980s. Formaldehyde
and acetaldehyde show reductions of 14% and 8% respectively from 1996-1998 to
2003-2005. It is not clear that these represent statistically significant reductions.
3. Emissions Inventory of TAC
For permitted stationary sources, an annual inventory of speciated TAC emissions
and facility locations were available as a part of BAAQMD's routine records. For
other source types, we applied a “top-down” approach, wherein source-specific
chemical speciation profiles were applied to total organic gas (TOG) and parti-
culate matter (PM) emissions to estimate the fractions released as TAC. In addition,
county-level emissions were mapped to source-specific areas using representative
geographic data. For example, ship emissions were mapped to shipping lanes in
the bay and ocean.
Weighting factors were applied to scale the emissions of each TAC according
to its toxicity for cancerous effects, non-cancerous chronic effects, and acute
effects. The details of inventory preparation, as well as findings and caveats, are
described elsewhere (Reid et al., 2006).
Comparison of various emission species revealed that diesel particulate matter
(diesel PM) contributes more than 85% of the cancer-risk-weighted emissions
(Fig. 1a
). On-road vehicles and off-road mobile sources are the primary sources of
diesel PM (
Fig. 1b).
The highest diesel PM emissions occur in core urban areas
and along major freeways (
Fig. 1c)
. The main contributor to chronic non-cancer
and acute health effects in the Bay Area is acrolein (not shown) whose major
sources include cars, trucks, and aircraft. Comparison of the maps of demographic
and health data (not shown) to TAC emissions (
Fig. 1c)
reveals that high TAC
emissions occur near areas with sensitive populations.
