10
L. R. F. Henneman et al.
2.1 Introduction
Air quality policies have long targeted the highest O 3 concentrations, and regulations
in place since mid-1990s have largely been successful at reducing these concentrations [1]. Recently established health-based standards, however, have prescribed
increasingly lower O 3 concentrations, which presumably call for further emissions
reductions.
The effectiveness of future emissions reductions, however, depends on the continued responsiveness of O 3 concentrations to emissions changes. OPE—the number
of O 3 molecules formed per NO X molecule emitted—has been used previously to
assess the potential for reducing O 3 with NO X emissions reductions. A high OPE, for
example, suggests greater effectiveness at reducing O 3 with future emissions cuts.
We endeavour to investigate how O 3 will continue to respond to emissions reductions
at increasingly low NO Z concentrations.
2.2 Method
2.2.1 Chemical Transport Model-Based OPE
We assess changing concentrations of gaseous air pollution species throughout the
eastern United States using the Community Multiscale Air Quality model with the
Decoupled Direct Method (CMAQ–DDM) version 5.0 with a 12 km resolution [2].
Meteorological fields for years 2001 and 2011 were processed using the Weather
Research Forecast (WRF) model version 3.6.1 Emissions were processed using EPA
SMOKE platforms for the 2002 and 2011 National Emissions Inventories. CMAQ
modelling was evaluated in detail by Henneman et al. [3].
We model concentrations and sensitivities to power plant and mobile emissions sources in four July scenarios: one each in years 2001 (2001 B ASE ) and 2011
(2011 B ASE ), and two hypothetical scenarios with 2011 meteorology—the first with
50% NO X emissions reductions (2011 50%N O X ) and the second with 90% emissions
reductions (2011 10%N O X ). Concentrations and sensitivities used in the OPE calculations below were taken as the average from 2 to 3 pm local time to match previous
studies.
OPEs were calculated with multiple approaches. The first, a brute force method,
assumes linear changes in OPE:
O P E
B F
=
O 3
N O Z
(2.1)
where denotes changing concentrations for the same locations and time of O 3
and NO Z (the sum of NO X reaction products: peroxyacetyl nitrate, peroxynitric acid,
L. R. F. Henneman et al.
2.1 Introduction
Air quality policies have long targeted the highest O 3 concentrations, and regulations
in place since mid-1990s have largely been successful at reducing these concentrations [1]. Recently established health-based standards, however, have prescribed
increasingly lower O 3 concentrations, which presumably call for further emissions
reductions.
The effectiveness of future emissions reductions, however, depends on the continued responsiveness of O 3 concentrations to emissions changes. OPE—the number
of O 3 molecules formed per NO X molecule emitted—has been used previously to
assess the potential for reducing O 3 with NO X emissions reductions. A high OPE, for
example, suggests greater effectiveness at reducing O 3 with future emissions cuts.
We endeavour to investigate how O 3 will continue to respond to emissions reductions
at increasingly low NO Z concentrations.
2.2 Method
2.2.1 Chemical Transport Model-Based OPE
We assess changing concentrations of gaseous air pollution species throughout the
eastern United States using the Community Multiscale Air Quality model with the
Decoupled Direct Method (CMAQ–DDM) version 5.0 with a 12 km resolution [2].
Meteorological fields for years 2001 and 2011 were processed using the Weather
Research Forecast (WRF) model version 3.6.1 Emissions were processed using EPA
SMOKE platforms for the 2002 and 2011 National Emissions Inventories. CMAQ
modelling was evaluated in detail by Henneman et al. [3].
We model concentrations and sensitivities to power plant and mobile emissions sources in four July scenarios: one each in years 2001 (2001 B ASE ) and 2011
(2011 B ASE ), and two hypothetical scenarios with 2011 meteorology—the first with
50% NO X emissions reductions (2011 50%N O X ) and the second with 90% emissions
reductions (2011 10%N O X ). Concentrations and sensitivities used in the OPE calculations below were taken as the average from 2 to 3 pm local time to match previous
studies.
OPEs were calculated with multiple approaches. The first, a brute force method,
assumes linear changes in OPE:
O P E
B F
=
O 3
N O Z
(2.1)
where denotes changing concentrations for the same locations and time of O 3
and NO Z (the sum of NO X reaction products: peroxyacetyl nitrate, peroxynitric acid,