Trace Metals in Soot and PM_2.5 from Heavy-Fuel-Oil Combustion in a Marine Engine

Abstract

Heavy fuel oil (HFO) particulate matter (PM) emitted by marine engines is known to contain toxic heavy metals, including vanadium (V) and nickel (Ni). The toxicity of such metals will depend on the their chemical state, size distribution, and mixing state. Using online soot-particle aerosol mass spectrometry (SP-AMS), we quantified the mass of five metals (V, Ni, Fe, Na, and Ba) in HFO-PM soot particles produced by a marine diesel research engine. The in-soot metal concentrations were compared to in-PM2.5 measurements by inductively coupled plasma-optical emission spectroscopy (ICP-OES). We found that <3% of total PM2.5 metals was associated with soot particles, which may still be sufficient to influence in-cylinder soot burnout rates. Since these metals were most likely present as oxides, whereas studies on lower-temperature boilers report a predominance of sulfates, this result implies that the toxicity of HFO PM depends on its combustion conditions. Finally, we observed a 4-to-25-fold enhancement in the ratio V:Ni in soot particles versus PM2.5, indicating an enrichment of V in soot due to its lower nucleation/condensation temperature. As this enrichment mechanism is not dependent on soot formation, V is expected to be generally enriched within smaller HFO-PM particles from marine engines, enhancing its toxicity.

Infrared-absorbing carbonaceous tar can dominate light absorption by marine-engine exhaust

“…49 All of these effects would be nullified by solvent extraction. Similarly, separate measurements of vanadium (the major trace metal in HFO-PM and in our samples 50 ) emission factors did not correlate with the AAE (370,880) ( Supplementary Figure 2), ruling out the possibility that inorganic species contributed significantly to our observed HFO-PM light absorption.…”

Brown and Black Carbon Emitted by a Marine Engine Operated on Heavy Fuel Oil and Distillate Fuels: Optical Properties, Size Distributions, and Emission Factors

“…Further analysis of independent size‐resolved composition measurements for HFO (Corbin et al, ) support this picture. Ash (metal oxides and/or sulfates) is also expected in the HFO PM, as discussed in Corbin et al ().…”

“…Further analysis of independent size‐resolved composition measurements for HFO (Corbin et al, ) support this picture. Ash (metal oxides and/or sulfates) is also expected in the HFO PM, as discussed in Corbin et al (). However, with the measurements presented here, we can only infer that ash particles did not make up the majority of the total particle mass for either rBC or OM/sulfate particles.…”

“…We therefore hypothesize that variable amounts of externally mixed ash particles were the main cause of the variability in the SSA 780nm . Such ash particles were identified by electron microscopy in these samples (Corbin et al, ), but more data would be needed to quantitatively evaluate this hypothesis.…”

Trends in PM2.5 transition metals in urban areas across the United States

“…The dominant source of Ni in NYC is boilers used for heating during winter while V appears to come predominantly from the port of NY, likely from marine engine emissions [48]. It should be noted that changing combustion conditions under constant fuel composition can dramatically alter the V:Ni emission ratios for marine engines [52]. The decreasing correlation shown in figure S23 is likely due to fuel-S regulations, which have the unintended benefit of also reducing transition metals (V) in the fuel [45].…”