4 research outputs found
Comparison of regional and global land cover products and the implications for biogenic emission modeling
<div><p>Accurate estimates of biogenic emissions are required for air quality models that support the development of air quality management plans and attainment demonstrations. Land cover characterization is an essential driving input for most biogenic emissions models. This work contrasted the global Moderate Resolution Imaging Spectroradiometer (MODIS) land cover product against a regional land cover product developed for the Texas Commissions on Environmental Quality (TCEQ) over four climate regions in eastern Texas, where biogenic emissions comprise a large fraction of the total inventory of volatile organic compounds (VOCs) and land cover is highly diverse. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) was utilized to investigate the influences of land cover characterization on modeled isoprene and monoterpene emissions through changes in the standard emission potential and emission activity factor, both separately and simultaneously. In Central Texas, forest coverage was significantly lower in the MODIS land cover product relative to the TCEQ data, which resulted in substantially lower estimates of isoprene and monoterpene emissions by as much as 90%. Differences in predicted isoprene and monoterpene emissions associated with variability in land cover characterization were primarily caused by differences in the standard emission potential, which is dependent on plant functional type. Photochemical modeling was conducted to investigate the effects of differences in estimated biogenic emissions associated with land cover characterization on predicted ozone concentrations using the Comprehensive Air Quality Model with Extensions (CAMx). Mean differences in maximum daily average 8-hour (MDA8) ozone concentrations were 2 to 6 ppb with maximum differences exceeding 20 ppb. Continued focus should be on reducing uncertainties in the representation of land cover through field validation.</p><p>Implications: <i>Uncertainties in the estimation of biogenic emissions associated with the characterization of land cover in global and regional data products were examined in eastern Texas. Misclassification between trees and low-growing vegetation in central Texas resulted in substantial differences in isoprene and monoterpene emission estimates and predicted ground-level ozone concentrations. Results from this study indicate the importance of land cover validation at regional scales</i>.</p></div
Regional Ozone Impacts of Increased Natural Gas Use in the Texas Power Sector and Development in the Eagle Ford Shale
The combined emissions and air quality
impacts of electricity generation
in the Texas grid and natural gas production in the Eagle Ford shale
were estimated at various natural gas price points for the power sector.
The increased use of natural gas in the power sector, in place of
coal-fired power generation, drove reductions in average daily maximum
8 h ozone concentration of 0.6–1.3 ppb in northeastern Texas
for a high ozone episode used in air quality planning. The associated
increase in Eagle Ford upstream oil and gas production nitrogen oxide
(NO<sub><i>x</i></sub>) emissions caused an estimated local
increase, in south Texas, of 0.3–0.7 ppb in the same ozone
metric. In addition, the potential ozone impacts of Eagle Ford emissions
on nearby urban areas were estimated. On the basis of evidence from
this work and a previous study on the Barnett shale, the combined
ozone impact of increased natural gas development and use in the power
sector is likely to vary regionally and must be analyzed on a case
by case basis
Dynamic Management of NO<sub><i>x</i></sub> and SO<sub>2</sub> Emissions in the Texas and Mid-Atlantic Electric Power Systems and Implications for Air Quality
Cap
and trade programs have historically been designed to achieve
annual or seasonal reductions in emissions of nitrogen oxides and
sulfur dioxide from power plants. Emissions reductions may not be
temporally coincident with meteorological conditions conducive to
the formation of peak ozone and fine particulate matter concentrations.
Integrated power system and air quality modeling methods were developed
to evaluate time-differentiated emissions price signals on high ozone
days in the Mid-Atlantic portion of the Pennsylvania–New Jersey–Maryland
(PJM) Interconnection and Electric Reliability Council of Texas (ERCOT)
grids. Sufficient flexibility exists in the two grids with marked
differences in demand and fuel generation mix to accommodate time-differentiated
emissions pricing alone or in combination with a season-wide program.
System-wide emissions reductions and production costs from time-differentiated
pricing are shown to be competitive with those of a season-wide program
on high ozone days and would be more cost-effective if the primary
policy goal was to target emissions reductions on these days. Time-differentiated
pricing layered as a complement to the Cross-State Air Pollution Rule
had particularly pronounced benefits for the Mid-Atlantic PJM system
that relies heavily on coal-fired generation. Time-differentiated
pricing aimed at reducing ozone concentrations had particulate matter
reduction co-benefits, but if particulate matter reductions are the
primary objective, other approaches to time-differentiated pricing
may lead to greater benefits
Flexible NO<sub><i>x</i></sub> Abatement from Power Plants in the Eastern United States
Emission controls that provide incentives for maximizing
reductions
in emissions of ozone precursors on days when ozone concentrations
are highest have the potential to be cost-effective ozone management
strategies. Conventional prescriptive emissions controls or cap-and-trade
programs consider all emissions similarly regardless of when they
occur, despite the fact that contributions to ozone formation may
vary. In contrast, a time-differentiated approach targets emissions
reductions on forecasted high ozone days without imposition of additional
costs on lower ozone days. This work examines simulations of such
dynamic air quality management strategies for NO<sub><i>x</i></sub> emissions from electric generating units. Results from a model
of day-specific NO<sub><i>x</i></sub> pricing applied to
the Pennsylvania–New Jersey–Maryland (PJM) portion of
the northeastern U.S. electrical grid demonstrate (i) that sufficient
flexibility in electricity generation is available to allow power
production to be switched from high to low NO<sub><i>x</i></sub> emitting facilities, (ii) that the emission price required
to induce EGUs to change their strategies for power generation are
competitive with other control costs, (iii) that dispatching strategies,
which can change the spatial and temporal distribution of emissions,
lead to ozone concentration reductions comparable to other control
technologies, and (iv) that air quality forecasting is sufficiently
accurate to allow EGUs to adapt their power generation strategies