Comparison of primary and secondary particle formation from natural gas engine exhaust and of their volatility characteristics
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 contribut...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/17/8739/2017/acp-17-8739-2017.pdf |
| Summary: | 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 kg<sub>fuel</sub><sup>−1</sup>. 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. |
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| ISSN: | 1680-7316 1680-7324 |