The effect of coal-fired power-plant SO<sub>2</sub> and NO<sub>x</sub> control technologies on aerosol nucleation in the source plumes
Nucleation in coal-fired power-plant plumes can greatly contribute to particle number concentrations near source regions. The changing emissions rates of SO<sub>2</sub> and NO<sub>x</sub> due to pollution-control technologies over recent decades may have had a significant eff...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2012-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/12/11519/2012/acp-12-11519-2012.pdf |
| Summary: | Nucleation in coal-fired power-plant plumes can greatly contribute to particle number concentrations near source regions. The changing emissions rates of SO<sub>2</sub> and NO<sub>x</sub> due to pollution-control technologies over recent decades may have had a significant effect on aerosol formation and growth in the plumes with ultimate implications for climate and human health. We use the System for Atmospheric Modeling (SAM) large-eddy simulation model with the TwO-Moment Aerosol Sectional (TOMAS) microphysics algorithm to model the nucleation in plumes of coal-fired plants. We test a range of cases with varying emissions to simulate the implementation of emissions-control technologies between 1997 and 2010. We start by simulating the W. A. Parish power plant (near Houston, TX) during this time period, when NO<sub>x</sub> emissions were reduced by ~90% and SO<sub>2</sub> emissions decreased by ~30%. Increases in plume OH (due to the reduced NO<sub>x</sub>) produced enhanced SO<sub>2</sub> oxidation and an order-of-magnitude increase in particle nucleation in the plume despite the reduction in SO<sub>2</sub> emissions. These results suggest that NO<sub>x</sub> emissions could strongly regulate particle nucleation and growth in power-plant plumes. Next, we test a range of cases with varying emissions to simulate the implementation of SO<sub>2</sub> and NO<sub>x</sub> emissions-control technologies. Particle formation generally increases with SO<sub>2</sub> emission, while NO<sub>x</sub> shows two different regimes: increasing particle formation with increasing NO<sub>x</sub> under low-NO<sub>x</sub> emissions and decreasing particle formation with increasing NO<sub>x</sub> under high-NO<sub>x</sub> emissions. Next, we compare model results with airborne measurements made in the W. A. Parish power-plant plume in 2000 and 2006, confirming the importance of NO<sub>x</sub> emissions on new particle formation and highlighting the substantial effect of background aerosol loadings on this process (the more polluted background of the 2006 case caused more than an order-of-magnitude reduction in particle formation in the plume compared to the cleaner test day in 2000). Finally, we calculate particle-formation statistics of 330 coal-fired power plants in the US in 1997 and 2010, and the model results show a median decrease of 19% in particle formation rates from 1997 to 2010 (whereas the W. A. Parish case study showed an increase). Thus, the US power plants, on average, show a different result than was found for the W. A. Parish plant specifically, and it shows that the strong NO<sub>x</sub> controls (90% reduction) implemented at the W. A. Parish plant (with relatively weak SO<sub>2</sub> emissions reductions, 30%) are not representative of most power plants in the US during the past 15 yr. These results suggest that there may be important climate implications of power-plant controls due to changes in plume chemistry and microphysics, but the magnitude and sign of the aerosol changes depend greatly on the relative reductions in NO<sub>x</sub> and SO<sub>2</sub> emissions in each plant. More extensive plume measurements for a range of emissions of SO<sub>2</sub> and NO<sub>x</sub> and in varying background aerosol conditions are needed, however, to better quantify these effects. |
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| ISSN: | 1680-7316 1680-7324 |