Brian K. Eder

A characterization of the spatiotemporal variability of non-urban ozone concentrations over the eastern United States

Abstract The spatial and temporal variability of the daily 1-h maximum O 3 concentrations over non-urban areas of the eastern United States of America was examined for the period 1985–1990 using principal component analysis. Utilization of Kaisers Varimax orthogonal rotation led to the delineation of six contiguous subregions or “influence regimes” which together accounted for 64.02% of the total variance. Each subregion displayed statistically unique O 3 characteristics and corresponded well with the path and frequency of anticyclones. When compared to the entire domain, the mid-Atlantic and south subregions observe higher mean daily 1-h maximum concentrations. Concentrations are near the domain average for the northeast and southwest subregions and are lowest in the Great Lakes and Florida subregions. The percentage of observations exceeding 120 ppb were greates in the mid-Atlantic and southwest subregions, near the domain average in the northeast and south subregions, and lowest in the Great Lakes and Florida subregions. Examination of the time series of the principal component scores associated with the subregions indicated that Great Lakes and mid-Atlantic subregions tend to observe a stronger seasonal cycle, with maximum concentrations occurring during the last week in June and first week in July, respectively. The strength of this seasonality is weakened for the northeast and south subregions and its timing delayed, until the end of July and the first of August, respectively. The southwest subregion experiences a greatly diminished seasonality, with maximum concentrations delayed until the middle of August. The seasonality found in the Florida subregion is unique in both its strength and timing, as the highest concentrations consistently occur during the months of April and May. The time series were then deseasonalized and autocorrelations and spectral density estimates calculated, revealing that persistence is much more prevalent in the Florida (autocorrelation significant to a lag of 4 days), south (3 days) and southwest (3 days) subregions. Conversely, autocorrelations are only significant to a lag of one day in the northeast and two days for the Great Lakes and mid-Atlantic subregions.

The New England Air Quality Forecasting Pilot Program: Development of an Evaluation Protocol and Performance Benchmark

Abstract The National Oceanic and Atmospheric Administration recently sponsored the New England Forecasting Pilot Program to serve as a “test bed” for chemical forecasting by providing all of the elements of a National Air Quality Forecasting System, including the development and implementation of an evaluation protocol. This Pilot Program enlisted three regional-scale air quality models, serving as prototypes, to forecast ozone (O3) concentrations across the northeastern United States during the summer of 2002. A suite of statistical metrics was identified as part of the protocol that facilitated evaluation of both discrete forecasts (observed versus modeled concentrations) and categorical forecasts (observed versus modeled exceedances/nonexceedances) for both the maximum 1-hr (125 ppb) and 8-hr (85 ppb) forecasts produced by each of the models. Implementation of the evaluation protocol took place during a 25-day period (August 5–29), utilizing hourly O3 concentration data obtained from over 450 monitors from the U.S. Environment Protection Agency’s Air Quality System network.

Attribution of the United States "warming hole": aerosol indirect effect and precipitable water vapor.

Aerosols can influence the climate indirectly by acting as cloud condensation nuclei and/or ice nuclei, thereby modifying cloud optical properties. In contrast to the widespread global warming, the central and south central United States display a noteworthy overall cooling trend during the 20th century, with an especially striking cooling trend in summertime daily maximum temperature (Tmax) (termed the U.S. “warming hole”). Here we used observations of temperature, shortwave cloud forcing (SWCF), longwave cloud forcing (LWCF), aerosol optical depth and precipitable water vapor as well as global coupled climate models to explore the attribution of the “warming hole”. We find that the observed cooling trend in summer Tmax can be attributed mainly to SWCF due to aerosols with offset from the greenhouse effect of precipitable water vapor. A global coupled climate model reveals that the observed “warming hole” can be produced only when the aerosol fields are simulated with a reasonable degree of accuracy as this is necessary for accurate simulation of SWCF over the region. These results provide compelling evidence of the role of the aerosol indirect effect in cooling regional climate on the Earth. Our results reaffirm that LWCF can warm both winter Tmax and Tmin.

Performance and Diagnostic Evaluation of Ozone Predictions by the Eta-Community Multiscale Air Quality Forecast System during the 2002 New England Air Quality Study

Abstract A real-time air quality forecasting system (Eta-Community Multiscale Air Quality [CMAQ] model suite) has been developed by linking the National Centers for Environmental Estimation Eta model to the U.S. Environmental Protection Agency (EPA) CMAQ model. This work presents results from the application of the Eta-CMAQ modeling system for forecasting ozone (O3) over the Northeastern United States during the 2002 New England Air Quality Study (NEAQS). Spatial and temporal performance of the Eta-CMAQ model for O3 was evaluated by comparison with observations from the EPA Air Quality System (AQS) network. This study also examines the ability of the model to simulate the processes governing the distributions of tropospheric O3 on the basis of the intensive datasets obtained at the four Atmospheric Investigation, Regional Modeling, Analysis, and Estimation (AIRMAP) and Harvard Forest (HF) surface sites. The episode analysis reveals that the model captured the buildup of O3 concentrations over the northeastern domain from August 11 and reproduced the spatial distributions of observed O3 very well for the daytime (8:00 p.m.) of both August 8 and 12 with most of normalized mean bias (NMB) within [H11006]20%. The model reproduced 53.3% of the observed hourly O3 within a factor of 1.5 with NMB of 29.7% and normalized mean error of 46.9% at the 342 AQS sites.The comparison of modeled and observed lidar O3 vertical profiles shows that whereas the model reproduced the observed vertical structure, it tended to overestimate at higher altitude. The model reproduced 64 –77% of observed NO2 photolysis rate values within a factor of 1.5 at the AIRMAP sites. At the HF site, comparison of modeled and observed O3/nitrogen oxide (NOx) ratios suggests that the site is mainly under strongly NOx-sensitive conditions (>53%). It was found that the modeled lower limits of the O3 production efficiency values (inferred from O3-CO correlation) are close to the observations.

General Circulation Model Output for Forest Climate Change Research and Applications

The report reviews technical aspects of and summarizes output from four climate models. Recommendations concerning the use of these outputs in forest impact assessments are made.

Using National Air Quality Forecast Guidance to Develop Local Air Quality Index Forecasts

The National Air Quality Forecast Capability (NAQFC) currently provides next-day forecasts of ozone concentrations over the contiguous United States. It was developed collaboratively by NOAA and Environmental Protection Agency (EPA) in order to provide state and local agencies, as well as the general public, air quality forecast guidance. As part of the development process, the NAQFC has been evaluated utilizing strict monitor-to-gridcell matching criteria, and discrete-type statistics of forecast concentrations. While such an evaluation is important to the developers, it is equally, if not more important, to evaluate the performance using the same protocol as the models intended application. Accordingly, the purpose of this article is to demonstrate the efficacy of the NAQFC from the perspective of a local forecaster, thereby promoting its use. Such an approach has required the development of a new evaluation protocol: one that examines the ability of the NAQFC to forecast values of the EPAs Air Qualit...

New Categorical Metrics for Air Quality Model Evaluation

Abstract Traditional categorical metrics used in model evaluations are “clear cut” measures in that the model’s ability to predict an “exceedance” is defined by a fixed threshold concentration and the metrics are defined by observation–forecast sets that are paired both in space and time. These metrics are informative but limited in evaluating the performance of air quality forecast (AQF) systems because AQF generally examines exceedances on a regional scale rather than a single monitor. New categorical metrics—the weighted success index (WSI), area hit (aH), and area false-alarm ratio (aFAR)—are developed. In the calculation of WSI, credits are given to the observation–forecast pairs within the observed exceedance region (missed forecast) or the forecast exceedance region (false alarm), depending on the distance of the points from the central line (perfect observation–forecast match line or 1:1 line on scatterplot). The aH and aFAR are defined by matching observed and forecast exceedances within an area ...

A climatology of total ozone mapping spectrometer data using rotated principal component analysis

The spatial and temporal variability of total column ozone (Ω) obtained from the total ozone mapping spectrometer (TOMS version 7.0) during the period 1980–1992 was examined through the use of a multivariate statistical technique called rotated principal component analysis. Utilization of Kaisers varimax orthogonal rotation led to the identification of 14, mostly contiguous subregions that together accounted for more than 70% of the total Ω variance. Each subregion displayed statistically unique Ω characteristics that were further examined through time series and spectral density analyses, revealing significant periodicities on semiannual, annual, quasi-biennial, and longer term time frames. This analysis facilitated identification of the probable mechanisms responsible for the variability of Ω within the 14 homogeneous subregions. The mechanisms were either dynamical in nature (i.e., advection associated with baroclinic waves, the quasi-biennial oscillation, or El Nino-Southern Oscillation) or photochemical in nature (i.e., production of odd oxygen (O or O3) associated with the annual progression of the Sun). The analysis has also revealed that the influence of a data retrieval artifact, found in equatorial latitudes of version 6.0 of the TOMS data, has been reduced in version 7.0.

Development of an Aggregation and Episode Selection Scheme to Support the Models-3 Community Multiscale Air Quality Model

Abstract The development of an episode selection and aggregation approach, designed to support distributional estimation for use with the Models-3 Community Multiscale Air Quality (CMAQ) model, is described. The approach utilized cluster analysis of the 700-hPa east–west and north–south wind field components over the time period of 1984–92 to define homogeneous meteorological clusters. Alternative schemes were compared using relative efficiencies and meteorological considerations. An optimal scheme was defined to include 20 clusters (five per season), and a stratified sample of 40 events was selected from the 20 clusters using a systematic sampling technique. The light-extinction coefficient, which provides a measure of visibility, was selected as the primary evaluative parameter for two reasons. First, this parameter can serve as a surrogate for particulate matter with diameter of less than 2.5 μm, for which few observational data exist. Second, of the air quality parameters simulated by CMAQ, this visib...

Modeling Ozone in the Chicago Urban Area

Ozone (O3) is a ubiquitous trace gas in the atmosphere. Its highest concentration is in the stratosphere, where it shields the earth’s surface from harmful ultraviolet radiation. At the surface, however, ozone is itself harmful, with destructive impacts on materials, crops, and health. Its levels have been high enough in certain areas to be of concern for several decades.