Stuart McKeen - Academia.edu (original) (raw)
Papers by Stuart McKeen
This study examines meteorological conditions associated with regional surface ozone using data c... more This study examines meteorological conditions associated with regional surface ozone using data collected during the summer Second Texas Air Quality Experiment, and the ability of the Nonhydrostatic Mesoscale Model-Community Multi-scale Air Quality Model (NMM-CMAQ) and the Weather Research and Forecast (WRF) model coupled with Chemistry (WRF-Chem) models to simulate the observed meteorology and surface ozone. The surface ozone data consist of 118 sites that are part of the U.S. Environmental Protection Agency Aerometric Information Retrieval Now (AIRNow) network, while the meteorological data came from a network of eleven 915-MHz wind profilers with RASS temperatures and supporting surface meteorological stations. High and low 8-h maximum ozone occurrences most frequently develop as regional events, with similar ozone concentration patterns across all of east Texas, allowing for a separate analysis of high-and low-ozone day conditions. The ability of the NMM-CMAQ and WRF-Chem models to simulate the meteorologically distinct high-and low-ozone events is analyzed. Histograms of surface ozone show that both the NMM-CMAQ and WRF-Chem models underpredict the full range found in the observations. For low ozone values, the analysis indicates that the models have a positive bias because of too large of an ozone inflow boundary condition value over the Gulf of Mexico. In contrast, the models have a negative bias for very high ozone values that occur mostly in Houston and Dallas, which suggests that the urban emissions and/or chemistry is misrepresented in the models.
Journal of Geophysical Research, 1999
Extensive observations of tropospheric trace species during the second NASA Global Tropospheric E... more Extensive observations of tropospheric trace species during the second NASA Global Tropospheric Experiment Western Pacific Exploratory Mission (PEM-West B) in February-March 1994 showed significant seasonal variability in comparison with the first mission (PEM-West A), conducted in September-October 1991.
Monthly Weather Review, 2005
Abstract In this paper, solar irradiance forecasts made by mesoscale numerical weather prediction... more Abstract In this paper, solar irradiance forecasts made by mesoscale numerical weather prediction models are compared with observations taken during three air-quality experiments in various parts of the United States. The authors evaluated the fifth-...
Journal of Geophysical Research, 1991
In order to better understand the photochemical and meteorological processes controlling regional... more In order to better understand the photochemical and meteorological processes controlling regional scale air quality problems such as ozone formation, we have developed a three-dimensional Eulerian model and applied this model to a high-pressure period (July 4 to July 7, 1986) ...
Journal of Geophysical Research, 1991
ABSTRACT A comprehensive three-dimensional mesoscale model, with detailed treatment of meteorolog... more ABSTRACT A comprehensive three-dimensional mesoscale model, with detailed treatment of meteorology and photochemistry, is applied to the eastern United States and southeastern Canada to address the issue of ozone production over rural regions. Simulations with various anthropogenic emission reductions over a 4-day high-pressure period, for which the eastern U.S. experienced elevated O3 levels, are compared to the results of a reference case that incorporates the most recent National Acid Precipitation Assessment Program (1985) emissions inventory. Our focus is on the relative effects of anthropogenic NOx versus nonmethane hydrocarbons (NMHC) emission reductions on O3 concentrations within this photochemical regime. The model results are consistent with earlier studies that predict a reasonably high O3 sensitivity to NMHC emission reductions, and O3 increases for NOx emission reductions in regions of strong urban influence. However, the total area that exhibits these distinctly urban characteristics comprises less than 10% of the continental area within the model. O3 production for the majority of the eastern United States is found to be limited by NOx availability rather than NMHC. Thus the sensitivity to NOx emission reductions averaged over the continental regions of the model domain is about a factor of 3 higher than that of NMHC. Because of large uncertainties in the natural and anthropogenic NMHC emissions, additional sensitivity runs are performed with increased anthropogenic NMHC emissions and natural NMHC emissions excluded. These alterations do not effect our basic conclusions with respect to rural O3 formation but do impact urban locations. When anthropogenic NMHC emissions are increased by a factor of 4, control Of NOx emissions has nearly the same effect in both urban and rural areas. The nonlinear nature of regionally averaged O3 with respect to anthropogenic and natural precursors is also illustrated from the results of the sensitivity studies.
Journal of Geophysical Research-Atmospheres, 2013
Nature, Jan 16, 2014
The United States is now experiencing the most rapid expansion in oil and gas production in four ... more The United States is now experiencing the most rapid expansion in oil and gas production in four decades, owing in large part to implementation of new extraction technologies such as horizontal drilling combined with hydraulic fracturing. The environmental impacts of this development, from its effect on water quality to the influence of increased methane leakage on climate, have been a matter of intense debate. Air quality impacts are associated with emissions of nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs), whose photochemistry leads to production of ozone, a secondary pollutant with negative health effects. Recent observations in oil- and gas-producing basins in the western United States have identified ozone mixing ratios well in excess of present air quality standards, but only during winter. Understanding winter ozone production in these regions is scientifically challenging. It occurs during cold periods of snow cover when meteorological inversions concentrate air pollutants from oil and gas activities, but when solar irradiance and absolute humidity, which are both required to initiate conventional photochemistry essential for ozone production, are at a minimum. Here, using data from a remote location in the oil and gas basin of northeastern Utah and a box model, we provide a quantitative assessment of the photochemistry that leads to these extreme winter ozone pollution events, and identify key factors that control ozone production in this unique environment. We find that ozone production occurs at lower NOx and much larger VOC concentrations than does its summertime urban counterpart, leading to carbonyl (oxygenated VOCs with a C = O moiety) photolysis as a dominant oxidant source. Extreme VOC concentrations optimize the ozone production efficiency of NOx. There is considerable potential for global growth in oil and gas extraction from shale. This analysis could help inform strategies to monitor and mitigate air quality impacts and provide broader insight into the response of winter ozone to primary pollutants.
Geophysical research letters, 2000
An upper limit for the gas phase absorption cross sections for H2SO 4 over the wavelength range 1... more An upper limit for the gas phase absorption cross sections for H2SO 4 over the wavelength range 195 to 330 nm has been determined. Absorption measurements were made using a diode array spectrometer and a 100 cm long heated absorption cell. Gas phase H2SO 4 was generated in a gas flow by titrating (equilibrating)known mounts of SO 3 via the reaction 803 + H20 <"-> H2804
Journal of Geophysical Research, 1995
The sources of photochemical precursors for ozone, primarily NOx (NO + NO2) and reduced carbon (C... more The sources of photochemical precursors for ozone, primarily NOx (NO + NO2) and reduced carbon (CO and hydrocarbons), were evaluated using principal component analysis (PCA) of concurrent measurements of [NOx], [NOv] (total reactive oxidized nitrogen species), [CO], [SO2], [C3H8], [C6H6], and [03] collected at a rural Alabama field site during the summers of 1990 and 1992. Two separate data matrices were analyzed, including a low measurement frequency matrix that included all of the variables and a high measurement frequency matrix that included all of the variables except for the hydrocarbons. The results of the PCA indicated that the major sources of NOv in the region are (1) coal-fired power plants and (2) biomass burning and/or paper mills. The identifications are based on the [CO]/[NOv] and [SO2]/[NOv] emission ratios derived from the measurements in comparison with the expected emission ratios that are based upon the National Acid Precipitation Assessment Program (NAPAP) emission inventory and upon laboratory experiments. The results indicated that the NAPAP inventory, integrated over the southeastern region of the United States, may overestimate the current [SO2]/[NOv] emission ratio from coal-fired power plants and may underestimate the [CO]/[NOv] emission ratio from paper mills. The results also suggest that biomass burning in the southeastern United States may be an important component in the NOv inventory, both as a point source associated with paper mills and as a seasonally dependent area source. The variation of [03] observed at the site was primarily related to the variation of [NOv]. Introduction Photochemical production of ozone in the troposphere is a process of great importance because increasing levels of ozone affect the atmospheric environment both as a secondary pollutant and as a greenhouse gas. To estimate this photochemical production [McKeen et al., 1991], it is necessary to determine the sources and distribution of the ozone precursors, NOx (NO q-NO2) and reduced carbon (CO + hydrocarbons). However, photochemical production of ozone is often NOx limited, particularly in the rural and remote troposphere [Liu et al., 1987; Trainer et al., 1987, 1993]. Hence quantitative regional and global inventories of NOx sources are critical for numerical modeling of atmospheric ozone. Generally speaking, in the industrialized nations of the world the sources of NO and, subsequently, NOx are thought to be dominated by point sources such as coal-fired power plants and paper mills and area sources such as automobile and soil emissions [e.g., Saeger et al., 1989; Williams et al., 1992; Pinkerton, 1993]. In addition to these widely recognized NOx Paper number 95JD01837. 0148-0227/95/95JD-01837505.00 sources, increased attention recently has been given to the role of biomass burning as a significant NOx source. This burning is associated with widespread agricultural practices used in less industrialized regions and has been cited as an important factor in determining the ozone formation in the tropics and the southern hemisphere [e.g., Crutzen et al., 1990; Lobert et al., 1991] as well as in the Arctic [Wofsy et al., 1992]. However, in the contiguous United States the role that biomass burning may play as a local or regional source of NOx as well as a variety of other compounds has been less studied. The impact of biomass burning on atmospheric composition is most likely in the less heavily populated and industrialized Southeast where extensive biomass burning is associated with the forest products industry. However, given the wide range of emissions possible from biomass burning depending on the condition of the biomass and the meteorology attendant to the burn [cf., Lobert et al., 1991], a priori quantification of this source and determining its importance relative to other NOx sources in the region presents a challenging problem. Several methods for identifying pollutant sources based on principal component analysis (PCA) have been presented in the literature [Greaves et al., 1987; Buhr et al., 1992; Henry et al., 1994]. In this paper, in an effort to classify the sources of NOx observed in the Southeast, a targeted PCA method is applied to measurements of NOy (where NOr = NOx + PAN + HNO3 + '") SO2, CO, benzene, propane, and ozone. Air masses were characterized using PCA and were classified with respect to source type. Identification of source type was made 22,853 22,854
A B S T R A C T Kalman filtering (KF) is used to estimate systematic errors in surface ozone fore... more A B S T R A C T Kalman filtering (KF) is used to estimate systematic errors in surface ozone forecasts. The KF updates its estimate of future ozone-concentration bias using past forecasts and observations. The optimum filter parameter is estimated via sensitivity analysis. KF performance is tested for deterministic, ensemble-averaged and probabilistic forecasts. Eight simulations were run for 56 d during summer 2004 over northeastern USA and southern Canada, with 358 ozone surface stations.
Aircraft, radiosonde, surface-flux, and boundary-layer wind profiler data from the Cooperative At... more Aircraft, radiosonde, surface-flux, and boundary-layer wind profiler data from the Cooperative Atmosphere Surface Exchange Study's 1997 field project, CASES-97, are combined with synoptic data to study the evolution of the vertically-averaged mixed-layer potential temperature [ ] and mixing-ratio [Q] on three nearly-cloudless days from 1000 CST to 1200 CST (local noon is approximately 1230 CST). This was achieved through examination of the terms in the time-tendency ('budget') equations for [ ] and [Q]. We estimate three of the terms -local time rate of change, vertical flux divergence, and horizontal advection. For the [Q]-budget, vertical flux divergence usually dominates, but horizontal advection is significant on one of the three days. The [Q]-budget balances for two of the three days to within the large experimental error. For the -budget, vertical flux divergence accounts for most of the morning warming, with horizontal advection of secondary importance. The residual in the -budget has the same sign for all three days, indicating that not all the heating is accounted for. We can balance the [ ]-budgets to within experimental error on two of the three days by correcting the vertical-flux divergence for apparent low biases in the flux measurements of one of the aircraft and in the surface fluxes, and accounting for direct heating of the mixed layer by radiative flux divergence allowing for the effects of carbonaceous aerosols. The [ ]-budget with these corrections also balances on the third day if horizontal gradients from synoptic maps are used to estimate the horizontal advection. However, the corrected budget for this day does not balance if the horizontal gradient in the advection term is estimated using CASES-97 aircraft and radiosondes; we suggest that persistent mesoscale circulations led to an overestimate of the horizontal gradient and hence horizontal advection.
Journal of Geophysical …, 1997
This study examines meteorological conditions associated with regional surface ozone using data c... more This study examines meteorological conditions associated with regional surface ozone using data collected during the summer Second Texas Air Quality Experiment, and the ability of the Nonhydrostatic Mesoscale Model-Community Multi-scale Air Quality Model (NMM-CMAQ) and the Weather Research and Forecast (WRF) model coupled with Chemistry (WRF-Chem) models to simulate the observed meteorology and surface ozone. The surface ozone data consist of 118 sites that are part of the U.S. Environmental Protection Agency Aerometric Information Retrieval Now (AIRNow) network, while the meteorological data came from a network of eleven 915-MHz wind profilers with RASS temperatures and supporting surface meteorological stations. High and low 8-h maximum ozone occurrences most frequently develop as regional events, with similar ozone concentration patterns across all of east Texas, allowing for a separate analysis of high-and low-ozone day conditions. The ability of the NMM-CMAQ and WRF-Chem models to simulate the meteorologically distinct high-and low-ozone events is analyzed. Histograms of surface ozone show that both the NMM-CMAQ and WRF-Chem models underpredict the full range found in the observations. For low ozone values, the analysis indicates that the models have a positive bias because of too large of an ozone inflow boundary condition value over the Gulf of Mexico. In contrast, the models have a negative bias for very high ozone values that occur mostly in Houston and Dallas, which suggests that the urban emissions and/or chemistry is misrepresented in the models.
Journal of Geophysical Research, 1999
Extensive observations of tropospheric trace species during the second NASA Global Tropospheric E... more Extensive observations of tropospheric trace species during the second NASA Global Tropospheric Experiment Western Pacific Exploratory Mission (PEM-West B) in February-March 1994 showed significant seasonal variability in comparison with the first mission (PEM-West A), conducted in September-October 1991.
Monthly Weather Review, 2005
Abstract In this paper, solar irradiance forecasts made by mesoscale numerical weather prediction... more Abstract In this paper, solar irradiance forecasts made by mesoscale numerical weather prediction models are compared with observations taken during three air-quality experiments in various parts of the United States. The authors evaluated the fifth-...
Journal of Geophysical Research, 1991
In order to better understand the photochemical and meteorological processes controlling regional... more In order to better understand the photochemical and meteorological processes controlling regional scale air quality problems such as ozone formation, we have developed a three-dimensional Eulerian model and applied this model to a high-pressure period (July 4 to July 7, 1986) ...
Journal of Geophysical Research, 1991
ABSTRACT A comprehensive three-dimensional mesoscale model, with detailed treatment of meteorolog... more ABSTRACT A comprehensive three-dimensional mesoscale model, with detailed treatment of meteorology and photochemistry, is applied to the eastern United States and southeastern Canada to address the issue of ozone production over rural regions. Simulations with various anthropogenic emission reductions over a 4-day high-pressure period, for which the eastern U.S. experienced elevated O3 levels, are compared to the results of a reference case that incorporates the most recent National Acid Precipitation Assessment Program (1985) emissions inventory. Our focus is on the relative effects of anthropogenic NOx versus nonmethane hydrocarbons (NMHC) emission reductions on O3 concentrations within this photochemical regime. The model results are consistent with earlier studies that predict a reasonably high O3 sensitivity to NMHC emission reductions, and O3 increases for NOx emission reductions in regions of strong urban influence. However, the total area that exhibits these distinctly urban characteristics comprises less than 10% of the continental area within the model. O3 production for the majority of the eastern United States is found to be limited by NOx availability rather than NMHC. Thus the sensitivity to NOx emission reductions averaged over the continental regions of the model domain is about a factor of 3 higher than that of NMHC. Because of large uncertainties in the natural and anthropogenic NMHC emissions, additional sensitivity runs are performed with increased anthropogenic NMHC emissions and natural NMHC emissions excluded. These alterations do not effect our basic conclusions with respect to rural O3 formation but do impact urban locations. When anthropogenic NMHC emissions are increased by a factor of 4, control Of NOx emissions has nearly the same effect in both urban and rural areas. The nonlinear nature of regionally averaged O3 with respect to anthropogenic and natural precursors is also illustrated from the results of the sensitivity studies.
Journal of Geophysical Research-Atmospheres, 2013
Nature, Jan 16, 2014
The United States is now experiencing the most rapid expansion in oil and gas production in four ... more The United States is now experiencing the most rapid expansion in oil and gas production in four decades, owing in large part to implementation of new extraction technologies such as horizontal drilling combined with hydraulic fracturing. The environmental impacts of this development, from its effect on water quality to the influence of increased methane leakage on climate, have been a matter of intense debate. Air quality impacts are associated with emissions of nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs), whose photochemistry leads to production of ozone, a secondary pollutant with negative health effects. Recent observations in oil- and gas-producing basins in the western United States have identified ozone mixing ratios well in excess of present air quality standards, but only during winter. Understanding winter ozone production in these regions is scientifically challenging. It occurs during cold periods of snow cover when meteorological inversions concentrate air pollutants from oil and gas activities, but when solar irradiance and absolute humidity, which are both required to initiate conventional photochemistry essential for ozone production, are at a minimum. Here, using data from a remote location in the oil and gas basin of northeastern Utah and a box model, we provide a quantitative assessment of the photochemistry that leads to these extreme winter ozone pollution events, and identify key factors that control ozone production in this unique environment. We find that ozone production occurs at lower NOx and much larger VOC concentrations than does its summertime urban counterpart, leading to carbonyl (oxygenated VOCs with a C = O moiety) photolysis as a dominant oxidant source. Extreme VOC concentrations optimize the ozone production efficiency of NOx. There is considerable potential for global growth in oil and gas extraction from shale. This analysis could help inform strategies to monitor and mitigate air quality impacts and provide broader insight into the response of winter ozone to primary pollutants.
Geophysical research letters, 2000
An upper limit for the gas phase absorption cross sections for H2SO 4 over the wavelength range 1... more An upper limit for the gas phase absorption cross sections for H2SO 4 over the wavelength range 195 to 330 nm has been determined. Absorption measurements were made using a diode array spectrometer and a 100 cm long heated absorption cell. Gas phase H2SO 4 was generated in a gas flow by titrating (equilibrating)known mounts of SO 3 via the reaction 803 + H20 <"-> H2804
Journal of Geophysical Research, 1995
The sources of photochemical precursors for ozone, primarily NOx (NO + NO2) and reduced carbon (C... more The sources of photochemical precursors for ozone, primarily NOx (NO + NO2) and reduced carbon (CO and hydrocarbons), were evaluated using principal component analysis (PCA) of concurrent measurements of [NOx], [NOv] (total reactive oxidized nitrogen species), [CO], [SO2], [C3H8], [C6H6], and [03] collected at a rural Alabama field site during the summers of 1990 and 1992. Two separate data matrices were analyzed, including a low measurement frequency matrix that included all of the variables and a high measurement frequency matrix that included all of the variables except for the hydrocarbons. The results of the PCA indicated that the major sources of NOv in the region are (1) coal-fired power plants and (2) biomass burning and/or paper mills. The identifications are based on the [CO]/[NOv] and [SO2]/[NOv] emission ratios derived from the measurements in comparison with the expected emission ratios that are based upon the National Acid Precipitation Assessment Program (NAPAP) emission inventory and upon laboratory experiments. The results indicated that the NAPAP inventory, integrated over the southeastern region of the United States, may overestimate the current [SO2]/[NOv] emission ratio from coal-fired power plants and may underestimate the [CO]/[NOv] emission ratio from paper mills. The results also suggest that biomass burning in the southeastern United States may be an important component in the NOv inventory, both as a point source associated with paper mills and as a seasonally dependent area source. The variation of [03] observed at the site was primarily related to the variation of [NOv]. Introduction Photochemical production of ozone in the troposphere is a process of great importance because increasing levels of ozone affect the atmospheric environment both as a secondary pollutant and as a greenhouse gas. To estimate this photochemical production [McKeen et al., 1991], it is necessary to determine the sources and distribution of the ozone precursors, NOx (NO q-NO2) and reduced carbon (CO + hydrocarbons). However, photochemical production of ozone is often NOx limited, particularly in the rural and remote troposphere [Liu et al., 1987; Trainer et al., 1987, 1993]. Hence quantitative regional and global inventories of NOx sources are critical for numerical modeling of atmospheric ozone. Generally speaking, in the industrialized nations of the world the sources of NO and, subsequently, NOx are thought to be dominated by point sources such as coal-fired power plants and paper mills and area sources such as automobile and soil emissions [e.g., Saeger et al., 1989; Williams et al., 1992; Pinkerton, 1993]. In addition to these widely recognized NOx Paper number 95JD01837. 0148-0227/95/95JD-01837505.00 sources, increased attention recently has been given to the role of biomass burning as a significant NOx source. This burning is associated with widespread agricultural practices used in less industrialized regions and has been cited as an important factor in determining the ozone formation in the tropics and the southern hemisphere [e.g., Crutzen et al., 1990; Lobert et al., 1991] as well as in the Arctic [Wofsy et al., 1992]. However, in the contiguous United States the role that biomass burning may play as a local or regional source of NOx as well as a variety of other compounds has been less studied. The impact of biomass burning on atmospheric composition is most likely in the less heavily populated and industrialized Southeast where extensive biomass burning is associated with the forest products industry. However, given the wide range of emissions possible from biomass burning depending on the condition of the biomass and the meteorology attendant to the burn [cf., Lobert et al., 1991], a priori quantification of this source and determining its importance relative to other NOx sources in the region presents a challenging problem. Several methods for identifying pollutant sources based on principal component analysis (PCA) have been presented in the literature [Greaves et al., 1987; Buhr et al., 1992; Henry et al., 1994]. In this paper, in an effort to classify the sources of NOx observed in the Southeast, a targeted PCA method is applied to measurements of NOy (where NOr = NOx + PAN + HNO3 + '") SO2, CO, benzene, propane, and ozone. Air masses were characterized using PCA and were classified with respect to source type. Identification of source type was made 22,853 22,854
A B S T R A C T Kalman filtering (KF) is used to estimate systematic errors in surface ozone fore... more A B S T R A C T Kalman filtering (KF) is used to estimate systematic errors in surface ozone forecasts. The KF updates its estimate of future ozone-concentration bias using past forecasts and observations. The optimum filter parameter is estimated via sensitivity analysis. KF performance is tested for deterministic, ensemble-averaged and probabilistic forecasts. Eight simulations were run for 56 d during summer 2004 over northeastern USA and southern Canada, with 358 ozone surface stations.
Aircraft, radiosonde, surface-flux, and boundary-layer wind profiler data from the Cooperative At... more Aircraft, radiosonde, surface-flux, and boundary-layer wind profiler data from the Cooperative Atmosphere Surface Exchange Study's 1997 field project, CASES-97, are combined with synoptic data to study the evolution of the vertically-averaged mixed-layer potential temperature [ ] and mixing-ratio [Q] on three nearly-cloudless days from 1000 CST to 1200 CST (local noon is approximately 1230 CST). This was achieved through examination of the terms in the time-tendency ('budget') equations for [ ] and [Q]. We estimate three of the terms -local time rate of change, vertical flux divergence, and horizontal advection. For the [Q]-budget, vertical flux divergence usually dominates, but horizontal advection is significant on one of the three days. The [Q]-budget balances for two of the three days to within the large experimental error. For the -budget, vertical flux divergence accounts for most of the morning warming, with horizontal advection of secondary importance. The residual in the -budget has the same sign for all three days, indicating that not all the heating is accounted for. We can balance the [ ]-budgets to within experimental error on two of the three days by correcting the vertical-flux divergence for apparent low biases in the flux measurements of one of the aircraft and in the surface fluxes, and accounting for direct heating of the mixed layer by radiative flux divergence allowing for the effects of carbonaceous aerosols. The [ ]-budget with these corrections also balances on the third day if horizontal gradients from synoptic maps are used to estimate the horizontal advection. However, the corrected budget for this day does not balance if the horizontal gradient in the advection term is estimated using CASES-97 aircraft and radiosondes; we suggest that persistent mesoscale circulations led to an overestimate of the horizontal gradient and hence horizontal advection.
Journal of Geophysical …, 1997