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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 8739-8755, 2017
https://doi.org/10.5194/acp-17-8739-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
18 Jul 2017
Comparison of primary and secondary particle formation from natural gas engine exhaust and of their volatility characteristics
Jenni Alanen1, Pauli Simonen1, Sanna Saarikoski2, Hilkka Timonen2, Oskari Kangasniemi1, Erkka Saukko1, Risto Hillamo2, Kati Lehtoranta3, Timo Murtonen3, Hannu Vesala3, Jorma Keskinen1, and Topi Rönkkö1 1Aerosol Physics, Faculty of Natural Sciences, Tampere University of Technology, P.O. Box 692, Tampere, Finland
2Atmospheric Composition Research, Finnish Meteorological Institute, P.O. Box 503, Helsinki, Finland
3VTT Technical Research Centre of Finland Ltd., P.O. Box 1000, Espoo, Finland
Abstract. Natural gas usage in the traffic and energy production sectors is a growing trend worldwide; thus, an assessment of its effects on air quality, human health and climate is required. Engine exhaust is a source of primary particulate emissions and secondary aerosol precursors, which both contribute to air quality and can cause adverse health effects. Technologies, such as cleaner engines or fuels, that produce less primary and secondary aerosols could potentially significantly decrease atmospheric particle concentrations and their adverse effects. In this study, we used a potential aerosol mass (PAM) chamber to investigate the secondary aerosol formation potential of natural gas engine exhaust. The PAM chamber was used with a constant UV-light voltage, which resulted in relatively long equivalent atmospheric ages of 11 days at most. The studied retro-fitted natural gas engine exhaust was observed to form secondary aerosol. The mass of the total aged particles, i.e., particle mass measured downstream of the PAM chamber, was 6–268 times as high as the mass of the emitted primary exhaust particles. The secondary organic aerosol (SOA) formation potential was measured to be 9–20 mg kgfuel−1. The total aged particles mainly consisted of organic matter, nitrate, sulfate and ammonium, with the fractions depending on exhaust after-treatment and the engine parameters used. Also, the volatility, composition and concentration of the total aged particles were found to depend on the engine operating mode, catalyst temperature and catalyst type. For example, a high catalyst temperature promoted the formation of sulfate particles, whereas a low catalyst temperature promoted nitrate formation. However, in particular, the concentration of nitrate needed a long time to stabilize – more than half an hour – which complicated the conclusions but also indicates the sensitivity of nitrate measurements on experimental parameters such as emission source and system temperatures. Sulfate was measured to have the highest evaporation temperature, and nitrate had the lowest. The evaporation temperature of ammonium depended on the fractions of nitrate and sulfate in the particles. The average volatility of the total aged particles was measured to be lower than that of primary particles, indicating better stability of the aged natural gas engine-emitted aerosol in the atmosphere. According to the results of this study, the exhaust of a natural gas engine equipped with a catalyst forms secondary aerosol when the atmospheric ages in a PAM chamber are several days long. The secondary aerosol matter has different physical characteristics from those of primary particulate emissions.

Citation: Alanen, J., Simonen, P., Saarikoski, S., Timonen, H., Kangasniemi, O., Saukko, E., Hillamo, R., Lehtoranta, K., Murtonen, T., Vesala, H., Keskinen, J., and Rönkkö, T.: Comparison of primary and secondary particle formation from natural gas engine exhaust and of their volatility characteristics, Atmos. Chem. Phys., 17, 8739-8755, https://doi.org/10.5194/acp-17-8739-2017, 2017.
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Short summary
Secondary organic and inorganic aerosols deteriorate air quality. Their formation from a natural gas engine was studied and compared with the emitted primary particulate emission. The volatility of the formed particles was defined as a function of temperature. Photochemical ages 4–11 days, mimicked by a potential aerosol mass chamber, produced 9–20 mg kg−1 fuel SOA. Aged emission particles were found to be less volatile than the fresh, implicating longer stability in the atmosphere.
Secondary organic and inorganic aerosols deteriorate air quality. Their formation from a natural...
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