Effects of Switching to Lower Sulfur Marine Fuel Oil
on Air Quality in the San Francisco Bay Area
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Abstract
Ocean-going vessels burning high-sulfur
heavy fuel oil are an important
source of air pollutants, such as sulfur dioxide and particulate matter.
Beginning in July 2009, an emission control area was put into effect
at ports and along the California coastline, requiring use of lower
sulfur fuels in place of heavy fuel oil in main engines of ships.
To assess impacts of the fuel changes on air quality at the Port of
Oakland and in the surrounding San Francisco Bay area, we analyzed
speciated fine particle concentration data from four urban sites and
two more remote sites. Measured changes in concentrations of vanadium,
a specific marker for heavy fuel oil combustion, are related to overall
changes in aerosol emissions from ships. We found a substantial reduction
in vanadium concentrations after the fuel change and a 28–72%
decrease in SO<sub>2</sub> concentrations, with the SO<sub>2</sub> decrease varying depending on proximity to shipping lanes. We estimate
that the changes in ship fuel reduced ambient PM<sub>2.5</sub> mass
concentrations at urban sites in the Bay area by about 3.1 ±
0.6% or 0.28 ± 0.05 μg/m<sup>3</sup>. The largest contributing
factor to lower PM mass concentrations was reductions in particulate
sulfate. Absolute sulfate reductions were fairly consistent across
sites, whereas trace metal reductions were largest at a monitoring
site in West Oakland near the port