Final Report: Characterization of Particulate Emissions from Ships from In Situ Measurements

EPA Grant Number: R834558
Title: Characterization of Particulate Emissions from Ships from In Situ Measurements
Investigators: Cappa, Christopher D
Institution: University of California - Davis
EPA Project Officer: Chung, Serena
Project Period: April 1, 2010 through March 31, 2013 (Extended to March 31, 2014)
Project Amount: $249,999
RFA: Novel Approaches to Improving Air Pollution Emissions Information (2009) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Air

Objective:

The objective(s) of this project are as follows: 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) to 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) to investigate variability in sources of black carbon in the near-shore marine boundary layer.

 

Summary/Accomplishments (Outputs/Outcomes):

Measurements of light absorption and extinction, and of the non-refractory chemical composition of ambient particulate matter were made during the 2010 CalNex field study onboard the Research Vessel Atlantis. Additional measurements of some gas-phase species, specifically CO2, CO, NOx, NOy, SO2 and HCHO, also were made. These measurements, along with meteorological data, were used to identify periods when plumes from nearby ships were encountered. Analysis of the in-plume and all-campaign measurements has led to the following findings.

  1. The influence of vessel speed on particulate and gas-phase emissions was assessed by sampling independent plumes from an individual vessel, the R/V Miller Freeman, while the Miller Freeman operated at different speeds. The Miller Freeman was a NOAA research vessel that operated a medium speed diesel engine and utilized a variable pitch propeller. During CalNex, the Miller Freeman was operating on ultra-low sulfur distillate fuel. The main components of the emitted particulate matter (PM) were black carbon (BC) and particulate organic matter (POM). Particulate sulfur emissions were negligible. The total particulate emissions factor (g-PM/kg-fuel) from the Miller Freeman increased as the vessel speed increased. This increase was the result of increases in both BC and POM-specific emission factors, although there appeared to be a slight shift towards greater relative POM as vessel speed increased. Regarding particle size, two modes were observed, one <100 nm and one > 100 nm in diameter. Overall, as the vessel speed increased the size of the small mode increased, from ~30 nm for the slowest intercept to ~70 nm for the largest intercept. A literature survey of the dependence of BC and POM on vessel speed was carried out to provide context for the Miller Freeman observations. The observed dependence of the PM, BC and POM emission factors on vessel speed for the Miller Freeman is somewhat different than had previously been observed for other vessels or test engines. This may reflect the use of a variable pitch propeller on the Miller Freeman. Overall, the literature survey indicated that there is not a clear relationship between BC or POM emissions and vessel speed that is generalizable across all vessel types and/or fuel types. Overall, the ability to make a clear assessment across vessel types is limited by the small number of ships/engines that have actually been sampled. It was also established that measurements of black carbon in fresh ship plumes made using a particular instrument, the single particle soot photometer (SP2), may be biased low due to a large fraction of the BC existing in particles that are below the SP2 minimum size detection limit. Finally, emission factors of gas-phase HCHO and CO decreased as vessel speed increased while emission factor for NOx increased with vessel speed. Full details can be found in Cappa et al. (2014).
  2. The variability in BC emission factors across all ships encountered during CalNex (71 in total) has been assessed. The average BC emission factor was 0.31 +/- 0.31 g-BC/kg-fuel, where the uncertainty reflects the variability between different ships and not the uncertainty in the individual measurements. Based on concurrent measurements of SO2 in the ship plumes, it was determined that all of the ships were operating on relatively low sulfur fuel, for example averaging 0.4% for ships operating slow speed diesel (SSD) engines, which corresponds to tanker and cargo ships. Ships operating high speed diesel (HSD) or medium speed diesel (MSD) engines were operating on even lower sulfur fuels. The low sulfur content of the fuels reflects the impact of rules regarding fuel sulfur for ships operating within the California regulated waters at the time. Only small differences in mean BC emission factors were observed during CalNex between ships that operated different speed engines (i.e. HSD, MSD and SSD). This contrasts with previous observations for ships operating in and around the Houston Ship Channel in 2006 (the TexAQS study; Lack et al., 2009). In that study, substantial differences in BC emission factors between MSD and the HSD and SSD classes, with the MSD being substantially larger. This reflects a bias of the MSD results towards a particular ship type during TexAQS, namely in use tug boats. Regarding the SSD class of vessels, the observed BC emission factors during CalNex were statistically significantly lower than those during TexAQS. It is hypothesized that the main reason for this difference is the use of different fuels by the SSD vessels between the studies. The SSD ships sampled during TexAQS operated on higher sulfur fuels, 1.6% on average. Higher sulfur content in fuels is typically associated with overall lower fuel quality (i.e. the fuel is less refined). These results suggest that the use of lower sulfur (higher quality) fuels by SSD vessels will likely lead to a reduction in BC emissions from ships. Finally, no identifiable dependence of the individual BC emission factors from each ship on ship speed was found, likely a reflection of ship-to-ship variability masking any specific dependence across the fleet. Full details can be found in Buffaloe et al. (2014).
  3. The dual dependence of vessel speed and fuel quality on PM emissions was assessed in a case study for an in use cargo ship, the Margrethe Maersk, during CalNex. In a coordinated effort with the NOAA WP-3D aircraft, emission plumes from the Margrethe Maersk were sampled as the ship transitioned from high sulfur heavy fuel oil (HFO; fuel sulfur content = 3.15%, ash content = 0.05%) to marine gas oil (MGO; fuel sulfur content = 0.07%, ash content < 0.01%) while simultaneously slowing as it approached the Port of Long Beach. In this manner, it was possible to establish how emission factors for total PM and for different PM components (e.g. BC, POM, sulfate) were affected by the change in fuel and speed. The decrease in fuel sulfur led to a dramatic drop in the emission factors for particulate sulfate (p-SO42-) and SO2. This decrease in particulate sulfate contributed to a decrease in the emitted number of cloud condensation nuclei, that was further exacerbated by a decrease in particle size. The change from HFO to MGO also corresponded to a decrease in POM and BC emission factors, consistent with the above assessment that BC emission factors during CalNex were smaller than those during TexAQS. These observations indicate that restrictions on low quality fuels (e.g. HFO) can lead to dramatic reductions in emissions of PM, and have important implications for the efficacy of near-coast fuel quality regulations. Full details are available in Lack et al. (2011).
  4. Measurements of light absorption and extinction by ambient particulate matter were made during CalNex both for particles as directly sampled (and dried) and particles that were subject to heating prior to measurement. The particles were heated by passing them through a thermodenuder. Heating of the particles leads to the evaporation of semivolatile materials, leaving behind low- and non-volatile materials, such as black carbon. The extent of loss of the semi- and low-volatility materials depends on the extent of heating. Additionally, measurements of the particle composition and size distribution behind the thermodenuder were also made. Specifically, measurements of the nonrefractory particle components and of components that were internally mixed with black carbon were made, the latter of which allows for assessment of the mean coating state of the BC-containing particles. It was established that the extent of coating increased with the extent of photochemical processing, indicating condensational growth of the BC-containing particles. It was found that the addition of this coating material to the BC did not lead to any appreciable change in the light absorption by the particles, as deduced from both the difference between the ambient and heated particle absorption and from the measured mass absorption coefficient (MAC), which is the ratio between the observed absorption and the concurrently observed BC concentration. This result was unexpected, since laboratory measurements have indicated that the addition of coatings to black carbon particles can lead to an increase in the absorption by those particles. Further, models that simulate the absorption by black carbon often account for the potential impact of the coatings by using core-shell Mie theory, in which the coating material and BC are assumed to exist as concentric spheres; core-shell Mie theory also indicates that coatings can lead to increases in absorption by BC above the uncoated value. These observations suggest that particle morphology plays an important role in determining the actual magnitude of the so-called absorption enhancement effect. Full details of this work are available in Cappa et al. (2012), Cappa et al. (2013). The results from CalNex were complemented with analysis of similar measurements made on air masses that were significantly impacted by particles from biomass burning, specifically from plumes sampled in Boulder, CO in 2011. Together with the CalNex observations, insights into the distinction between the absorption enhancements observed for anthropogenically derived BC (CalNex) vs. naturally-derived BC (Boulder) have been developed. It was established that the mean absorption enhancement for biomass-burning derived particles was substantially larger than that of even the “aged” particles sampled during CalNex. Further, light absorption by POM in addition to BC was found to be important at 405 nm, but not at 532 nm wavelength. These results provide context for understanding the impacts of coatings on BC absorption in disparate regions of the world, which is necessary to understand the global impact of BC particles on the Earth’s radiation budget. Full details of this work are available in Lack et al. (2012a). Finally, some limited laboratory experiments have been conducted in an effort to understand further the physical reasons for the differences between the observations in CalNex and Boulder, and the differences between the CalNex observations and laboratory/theoretical expectations.
  5. The primary measurements that form the core of the above studies were made using the UC Davis dual wavelength Cavity Ringdown-Photoacoustic Spectrometer (CRD-PAS). The CRD-PAS is used to measure light extinction and light absorption by particles at 405 nm and 532 nm wavelengths. Further, light extinction is measured for both dry particles and humidified particles simultaneously. The instruments used were deployed for the first time during CalNex, and were supplemented by complementary measurements made by us using an alternative CRD-PAS system that was borrowed from the NOAA Chemical Sciences Division. The design of the UC Davis PAS was new, and is documented in Lack et al. (2012b). 
  6. During CalNex, some of the time was spent sampling direct emissions of particulate matter generated from the ocean surface using the “sea-sweep.” The sea-sweep generates particles in situ from the ocean surface by bubbling clean air through the ocean surface. As the bubbles rise to the surface and escape to the atmosphere, the bursting motion leads to the emission of small particles. These particles were sampled by a multitude of instruments on board the R/V Atlantis, including the UC Davis CRD-PAS. Our specific contribution was to show that re-emission of BC from the ocean surface in the sampled waters was negligible. A comprehensive analysis of the sea-sweep observations by our collaborators is provided in Bates et al. (2012).

Conclusions:

Atmospheric aerosol particles have important influences on global climate, precipitation, visibility and human health. Direct emissions of particulate matter from commercial ships in coastal environments are a growing concern for human health, yet emissions inventories for ships are based on an extremely limited data set. Further, more stringent regulations regarding the quality of fuel used by ships have recently been put in place in the US and around the world, with expectations that the change in fuel quality would bring significant benefits to air quality in coastal regions due to substantial reductions in sulfur emissions. Our work has greatly expanded the data available regarding emissions of black carbon from in use ships, which will allow for the development of more robust emissions inventories. We have explicitly demonstrated from real world measurements that improvements in fuel quality (corresponding to reductions in the fuel sulfur content) do, indeed, lead to substantial reductions sulfur emissions from ships. We have shown that improvements in fuel quality may have additional benefits in that emissions of black carbon and particulate organic matter are also reduced when ships are operating on the higher quality fuels. Black carbon also has an important impact on climate through its ability to absorb solar radiation, which globally leads to increased temperatures. Accordingly, black carbon reductions have been targeted as a potential near-term climate mitigation strategy. Having clear quantitative understanding of the warming influence of black carbon is therefore critical to understanding the potential climate benefits of black carbon reductions. We have demonstrated that black carbon particles in the ambient atmosphere may not absorb sunlight as efficiently as some laboratory experiments suggest, which has implications for how absorption by black carbon is simulated within regional and global climate models.


Journal Articles on this Report : 10 Displayed | Download in RIS Format

Other project views: All 19 publications 10 publications in selected types All 10 journal articles
Type Citation Project Document Sources
Journal Article Bates TS, Quinn PK, Frossard AA, Russell LM, Hakala J, Petaja T, Kulmala M, Covert DS, Cappa CD, Li S-M, Hayden KL, Nuaaman I, McLaren R, Massoli P, Canagaratna MR, Onasch TB, Sueper D, Worsnop DR, Keene WC. Measurements of ocean derived aerosol off the coast of California. Journal of Geophysical Research-Atmospheres 2012;117(D21):D00V15 (13 pp.). R834558 (2011)
R834558 (2012)
R834558 (Final)
  • Full-text: AGU-Full Text PDF
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  • Abstract: AGU-Abstract & Full Text HTML
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  • Journal Article Buffaloe GM, Lack DA., Williams EJ, Coffman D, Hayden KL, Lerner BM, Li SM, Nuaaman I, Massoli P, Onasch TB, Quinn PK, Cappa CD. Black carbon emissions from in-use ships: a California regional assessment. Atmospheric Chemistry and Physics 2014;14(4):1881-1896. R834558 (Final)
  • Full-text: ACP-Full Text PDF
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  • Abstract: ACP-Abstract
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  • Journal Article Cappa CD, Onasch TB, Massoli P, Worsnop DR, Bates TS, Cross ES, Davidovits P, Hakala J, Hayden KL, Jobson BT, Kolesar KR, Lack DA, Lerner BM, Li S-M, Mellon D, Nuaanman I, Olfert JS, Petaja T, Quinn PK, Song C, Subramanian R, Williams EJ, Zaveri RA. Radiative absorption enhancements due to the mixing state of atmospheric black carbon. Science 2012;337(6098):1078-1081. R834558 (2012)
    R834558 (Final)
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  • Journal Article Cappa CD, Onasch TB, Massoli P, Worsnop DR, Bates TS, Cross ES, Davidovits P, Hakala J, Hayden KL, Jobson BT, Kolesar KR, Lack DA, Lerner BM, Li S-M, Mellon D, Nuaaman I, Olfert JS, Petaja T, Quinn PK, Song C, Subramanian R, Williams EJ, Zaveri RA. Response to comment on "Radiative Absorption Enhancements Due to the Mixing State of Atmospheric Black Carbon." Science 2013;339(6118):393. R834558 (2012)
    R834558 (Final)
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  • Journal Article Cappa CD, Williams EJ, Lack DA, Buffaloe GM, Coffman D, Hayden KL, Herndon SC, Lerner BM, Li S-M, Massoli P, McLaren R, Nuaaman I, Onasch TB, Quinn PK. A case study into the measurement of ship emissions from plume intercepts of the NOAA ship Miller Freeman. Atmospheric Chemistry and Physics 2014;14(3):1337-1352. R834558 (Final)
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  • Journal Article 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. R834558 (2010)
    R834558 (2011)
    R834558 (2012)
    R834558 (Final)
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  • Journal Article 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. R834558 (2010)
    R834558 (2011)
    R834558 (2012)
    R834558 (Final)
  • Full-text: Taylor&Francis-Full Text HTML
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  • Abstract: Taylor&Francis-Abstract
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  • Journal Article Lack DA, Langridge JM, Bahreini R, Cappa CD, Middlebrook AM, Schwarz JP. Brown carbon and internal mixing in biomass burning particles. Proceedings of the National Academy of Sciences of the United States of America 2012;109(37):14802-14807. R834558 (2012)
    R834558 (Final)
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  • Journal Article Massoli P, Onasch TB, Cappa CD, Nuamaan I, Hakala J, Hayden K , Li S-M, Sueper DT, Bates TS, Quinn PK, Jayne JT, Worsnop DR. Characterization of black carbon-containing particles from soot particle aerosol mass spectrometer measurements on the R/V Atlantis during CalNex 2010. Journal of Geophysical Research-Atmospheres 2015;120(6):2575-2593. R834558 (Final)
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  • Journal Article Zhang X, Massoli P, Quinn PK, Bates TS, Cappa CD. Hygroscopic growth of submicron and supermicron aerosols in the marine boundary layer. Journal of Geophysical Research-Atmospheres 2014;119(13):8384-8399. R834558 (Final)
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  • Supplemental Keywords:

    soot, Pacific coast, EPA Region 9, Environmental chemistry and engineering

    Progress and Final Reports:

    Original Abstract
  • 2010 Progress Report
  • 2011 Progress Report
  • 2012 Progress Report