2010 Progress Report: Characterization of Particulate Emissions from Ships from In Situ Measurements
EPA Grant Number:
Characterization of Particulate Emissions from Ships from In Situ Measurements
Cappa, Christopher D
University of California - Davis
EPA Project Officer:
April 1, 2010 through
March 31, 2013
(Extended to March 31, 2014)
Project Period Covered by this Report:
April 1, 2010 through March 31,2011
Novel Approaches to Improving Air Pollution Emissions Information (2009)
Air Quality and Air Toxics
The objective(s) of this project is to make and use measurements of light absorption and extinction by particles, in conjunction with other particle measurements, during the CalNex 2010 field campaign to (1) quantitatively characterize particulate emissions from ocean going vessels in the regulated waters along the California coast; (2) characterize the variability in the mass absorption coefficient for black carbon particles in the atmosphere, and to work towards understanding the origin of this variability; and (3) investigate variability in sources of black carbon in the near-shore marine boundary layer.
Measurements of light absorption and extinction were made during May/June 2010 on board the R/V Atlantis as part of the CalNex 2010 field campaign. Measurements also were tagged on as part of the CARES 2010 field campaign directly following CalNex, as this was in the same location and provided a useful extension of the CalNex data set. The optical property data collected by the University of California-Davis (UCD) group has been processed and final absorption and extinction data now are available (upon request for CalNex, to eventually be archived with NOAA, at http://www.arm.gov/campaigns/aaf2009carbonaerosol
for CARES). So far, these data have been used for the following analyses:
(1) Characterization of the influence of fuel quality on emissions of particulate matter from shipping activities a case study: In coordination with the NOAA WP-3D aircraft, we were able to make comprehensive measurements of how the emission factors for PM1 and the associated sulfate, organic matter, black carbon (BC), particle number and cloud condensation nuclei (CCN) number varied as an in-use, underway large cargo ship, the Margrethe Maersk, underwent a transition from using heavy fuel oil (HFO, a high sulfur, "dirty" fuel) to using marine gas oil (MGO, a lower-sulfur, much cleaner fuel) as it entered the regulated waters around California. Importantly, we saw that the change in fuel led to a significant reduction in the particulate mass emission factor (EF), driven primarily by a decrease in p-SO4. However, there also was a noticeable decrease in the BC EF and in the organic EF. Although the number of particles emitted was approximately conserved upon the fuel switch, the change in composition and the decrease in the mean particle diameter led to these particles being much less effective CCN. This study has immense implications for the implementation of further world-wide fuel-quality regulations associated with shipping activities. This work was published recently in ES&T.
(2) Effect of vessel speed on particulate emissions: As a case study, we have used the CalNex dataset to determine how PM and gas-phase emissions from an in-use vessel (a medium-speed diesel engine research vessel, the R/V Miller Freemen) depend on the ship speed. This type of information is useful because there has been some consideration towards the implementation of vessel speed reduction requirements near ports. Speed reduction tends to decrease the absolute emissions, due to increased fuel economy, but there is much less known about how the emissions factors actually change with vessel speed. We found that, for this vessel, a reduction in speed led to a significant decrease in the EFs for all particulate species measured, when considered in units of g-PM/kg-fuel consumed. In general, the particle size distribution shifted towards much smaller particles as ship speed decreased. For the gas-phase species, the variation in the EFs with vessel speed is species specific, with CO and HCHO tending to decrease, SO2 remaining constant, and NOx increasing as ship speed increased. Although for a medium-speed engine, this work helps to inform whether EF changes with speed reductions are likely to have a significant influence on the absolute emissions of pollutants in near port regions. A manuscript describing this work currently is being prepared for submission to a journal.
(3) Influence of fuel quality on PM emissions from ships: To move beyond the case study mentioned above, we have been working to compile results for BC EFs, total PM1 mass EFs and particle number EFs for all of the 90+ ship encounters during CalNex. All of these encounters took place within the California regulated waters, and thus the ships were (supposedly) using higher quality MGO instead of HFO. As such, our observations can be compared directly to the comprehensive measurements made as part of the TexAQS 2006 study (Lack, et al., 2008, 2009), where the majority of the ships were operating on HFO. Preliminary results suggest that, although the ship-to-ship variability is large, on the whole BC EFs from slow speed diesel ships (e.g., cargos, containers, tankers) are lower when they operate on MGO instead of HFO, by around a factor of 1.8. This average result is consistent with the observations of the Margrethe Maersk discussed above. Progress on this particular study has been steady, but an expansion to include other PM species (e.g., SO4 and organics) has been hampered by data availability from our collaborators.
(4) Variability in mass absorption coefficients for black carbon: It is thought that the presence of "coatings" on black carbon can lead to a significant increase in the absorption by BC particles, and thus an increase in the mass absorption coefficient of BC relative to "bare" particles. This has important implications for how large the positive climate forcing by BC particles is in the atmosphere, and also for how it is represented within climate models. We made measurements of light absorption behind a "thermodenuder" during both CalNex and CARES in order to compare the absorption with such coatings present to when they were removed. Interestingly, our analysis of the collected data indicates that the removal of the coatings has almost no influence on the light absorption properties of the BC particles, meaning that the coatings appear to do little to "enhance" the light absorption by BC. Further, we find that there is very little variability in the measured mass absorption coefficient, as determined from our light absorption measurements and measurements of BC mass from a single particle soot photometer (Environment Canada). Measurements of the coating-to-BC-core mass ratio for the BC-containing particles using the new soot photometer-aerosol mass spectrometer (Aerodyne) during CalNex clearly indicate that the particles had, in principle, sufficient material that large absorption enhancements should have been observed. These results suggest that ambient BC particles may not experience the large absorption enhancements in practice that theory suggests should occur and have implications for the representation of BC within climate models. This is likely a result of the particles not actually having an internal morphology that will lead to a significant enhancement. Analysis of these results is ongoing, but should result in a submitted publication shortly.
(5) Absorption Enhancements for BC in an idealized setting: In support of the observations discussed in point (4), we have been working to analyze results from a complementary laboratory study that took place in 2008, the so-called BC2 campaign at Boston College. In this study, light absorption measurements of laboratory generated BC (from an ethylene flame) were made where these BC particles were coated with varying amounts of "stuff" (either sulfuric acid or dioctyl sebacate [DOS]). We are using these measurements to understand to what extent we should expect to see an absorption enhancement for real-world BC particles. Our analysis indicates that for DOS-coated BC, such enhancements can occur and be explained quantitatively through theory, but for H2SO4 coatings the picture becomes much less clear and significant deviations from theory result. This work helps inform our ambient observations and provides a basis for understanding under what conditions the "expected" absorption enhancements will/will not be observed.
We plan to continue with the analyses discussed in points 2-5, with a goal of these being submitted for publication by the end of the upcoming reporting period.
on this Report
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|| Lack DA, Cappa CD, Langridge J, Bahreini R, Buffaloe G, Brock C, Cerully K, Coffman D, Hayden K, Holloway J, Lerner B, Massoli P, Li S-M, McLaren R, Middlebrook AM, Moore R, Nenes A, Nuaaman I, Onasch TB, Peischl J, Perring A, Quinn PK, Ryerson T, Schwartz JP, Spackman R, Wofsy SC, Worsnop D, Xiang B, Williams E. Impact of fuel quality regulation and speed reductions on shipping emissions:implications for climate and air quality. Environmental Science & Technology 2011;45(20):9052-9060.
Abstract from PubMed
Full-text: ES&T-Full Text HTML
Other: ES&T-Full Text PDF
|| Lack DA, Richardson MS, Law D, Langridge JM, Cappa CD, McLaughlin RJ, Murphy DM. Aircraft instrument for comprehensive characterization of aerosol optical properties, Part 2:black and brown carbon absorption and absorption enhancement measured with photo-acoustic spectroscopy. Aerosol Science and Technology 2012;46(5):555-568.
Full-text: Taylor&Francis-Full Text HTML
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Progress and Final Reports:
2011 Progress Report
2012 Progress Report