Ana Prados

Transport of ozone and pollutants from North America to the North Atlantic Ocean during the 1996 Atmosphere/Ocean Chemistry Experiment (AEROCE) intensive

Research flights were conducted to investigate the episodic occurrence of enhanced ozone mixing ratios over the North Atlantic Ocean (NAO) during the spring as part of the Atmosphere/Ocean Chemistry Experiment (AEROCE). We measured meteorological variables, trace gases, and aerosol light scattering from the University of Wyoming King Air research aircraft during 16 research flights in April and early May 1996. The flights were conducted over eastern North America and over the NAO between the United States and Bermuda. On April 28, a cold front was located just west of Bermuda while a second system developed over the Midwest and central United States. In the midtroposphere, polluted layers with up to 250 ppbv CO, 150 pptv NO, and 1.8 ppbv NO y were observed within a deeper layer of enhanced O 3 mixing ratios (up to 88 ppbv) over the NAO at around 32°N, 64-68°W. These aircraft observations, when coupled with ozone sondes, back trajectories, and satellite image loops, indicate two distinct meteorological mechanisms that combine to yield the observed chemical signature of the air. There is substantial meteorological evidence, supported by ozone sonde observations and earlier King Air flights, indicating that stratosphere/troposphere exchange associated with the upstream frontal system injects and advects dry, ozone-rich air into midtro-pospheric regions over the continent. These subsiding air masses have the potential to result in deep layers of enhanced ozone in the offshore postfrontal area. Convection from the developing (upwind) system appears to lift air from the continental boundary layer into the area of subsidence in the mid to upper troposphere. The result is high concentrations of gaseous and particulate pollutants along with elevated quantities of ozone. Ozone mixing ratios exceed those attributable to boundary layer venting or in-transit photochemical production. These meteorological processes lead to pollution and enhanced ozone from the stratosphere cooccurring in postfrontal air masses over the NAO.

Air Quality Forecast Verification Using Satellite Data

Abstract NOAA’s operational geostationary satellite retrievals of aerosol optical depths (AODs) were used to verify National Weather Service developmental (research mode) particulate matter (PM2.5) predictions tested during the summer 2004 International Consortium for Atmospheric Research on Transport and Transformation/New England Air Quality Study (ICARTT/NEAQS) field campaign. The forecast period included long-range transport of smoke from fires burning in Canada and Alaska and a regional-scale sulfate event over the Gulf of Mexico and the eastern United States. Over the 30-day time period for which daytime hourly forecasts were compared with observations, the categorical (exceedance defined as AOD > 0.55) forecast accuracy was between 0% and 20%. Hourly normalized mean bias (forecasts − observations) ranged between −50% and +50% with forecasts being positively biased when observed AODs were small and negatively biased when observed AODs were high. Normalized mean errors are between 50% and 100% with t...

An Improved Method for Estimating Surface Fine Particle Concentrations Using Seasonally Adjusted Satellite Aerosol Optical Depth

Abstract Using satellite observations of aerosol optical depth (AOD) to estimate surface concentrations of fine particulate matter (PM2.5) is a well-established technique in the air quality community. In this study, the relationships between PM2.5 concentrations measured at five monitor locations in the Baltimore, MD/Washington, DC region and AOD from Moderate Resolution Imaging Spectroradiometer (MODIS), Multi-Angle Imaging Spectroradiometer (MISR), and Geostationary Operational Environmental Satellite (GOES) were calculated for the summer of 2004 and all of 2005. Linear regression methods were used to determine the direct quantitative relationships between the satellite AOD values and PM2.5 concentration measurements. Results show that correlations between AOD and surface PM2.5 concentrations range from 0.46 to 0.84 for the analyzed time period. Correlations with AOD from MODIS and MISR were higher than those from GOES, likely because of variations in the algorithms used by the different instruments. To determine the relative usefulness of platform- and season-specific AOD PM2.5 regression analysis, the results from this study were used to estimate surface PM2.5 concentrations for two representative case studies. This analysis of case studies demonstrates that it is necessary to include season and satellite platform information for more accurate estimates of surface PM2.5 concentrations from satellite AOD data. Consequently, tools that currently use a constant relationship to estimate surface PM2.5 concentrations from satellite AOD data, such as the Infusing satellite Data into Environmental Applications (IDEA) website, may need to be revised to include parameters that allow the relationships to vary with season and satellite platform to provide more accurate results.

Applications of the three-dimensional air quality system to western U.S. air quality: IDEA, smog blog, smog stories, airquest, and the remote sensing information gateway.

Abstract A system has been developed to combine remote sensing and ground-based measurements of aerosol concentration and aerosol light scattering parameters into a three-dimensional view of the atmosphere over the United States. Utilizing passive and active remote sensors from space and the ground, the system provides tools to visualize particulate air pollution in near real time and archive the results for retrospective analyses. The main components of the system (Infusing satellite Data into Environmental Applications [IDEA], the U.S. Air Quality Web log [Smog Blog], Smog Stories, U.S. Environmental Protection Agency’s AIR Quest decision support system, and the Remote Sensing Information Gateway [RSIG]) are described, and the relationship of how data move from one system to another is outlined. To provide examples of how the results can be used to analyze specific pollution episodes, three events (two fires and one wintertime low planetary boundary layer haze) are discussed. Not all tools are useful at all times, and the limitations, including the sparsity of some data, the interference caused by overlying clouds, etc., are shown. Nevertheless, multiple sources of data help a state, local, or regional air quality analyst construct a more thorough picture of a daily air pollution situation than what one would obtain with only surface-based sensors.

Access, Visualization, and Interoperability of Air Quality Remote Sensing Data Sets via the Giovanni Online Tool

This paper describes the air quality data products and services available through Giovanni, a web based tool for access, visualization, and analysis of satellite remote sensing products, and also model output and surface observations relevant to global air quality. Available datasets include total column aerosol measurements from numerous satellite instruments, column NO2 and SO2, vertical aerosol products from CALIPSO, surface PM2.5 concentrations over the continental U.S, and speciated model Aerosol Optical Depth. Giovanni was designed to make satellite and ground-based data easier to use; it does not require separate access to or downloading of data sets, making the visualizations and analysis services accessible to both the novice and the experienced user. Giovanni air quality data products are provided on a common grid and can also be obtained in KMZ format for Google Earth visualization. This feature allows collocation of datasets to aid in analysis of pollution events and to facilitate satellite/monitor comparisons and aerosol intercomparison studies in a fraction of the time compared to traditional methods. Giovanni also supports multiple interoperability protocols which permit data sharing with other online tools, in order to enhance access to the datasets for improved air quality decision making. The Giovanni team is currently actively involved in several data networking initiatives with service oriented tools at other institutions such as DataFed.

Nonmethane hydrocarbon mixing ratios in continental outflow air from eastern North America: Export of ozone precursors to Bermuda

High surface ozone levels at Bermuda during springtime are associated with the transport of large scale frontal systems from the U.S. east coast over the North Atlantic. An objective of the AEROCE III study was to adopt a meteorologically informed sampling strategy of the chemical characteristics of air masses both in advance and behind eastward progressing cold fronts in order to differentiate between vertical sources of these elevated tropospheric ozone signals. Concentrations of hydrocarbons in air sampled over the eastern US and in offshore flights varied in a complex manner with sample altitude and prevailing meteorological situation. In several aircraft flights, the presence at altitude of distinct layers of air of elevated concentrations of NMHCs attested to the dynamic mixing of lower and upper air masses associated with springtime frontal activity. Layers of mid-tropospheric air of high O3 (140 ppbv) and low background NMHC mixing ratios (1.44 ppbv ethane, 0.034 ppbv propene, 0.247 ppbv propane, 0.034 ppbv isobutene, 0.041 ppbv n-butane, 0.063 ppbv benzene, 0.038 ppbv toluene) mixing ratios were indicative of descending, stratospherically influenced air on a flight to the east of Norfolk, VA on April 24 (alt 4600 m). Layers of high O3 (60–70 ppbv) and elevated NMHC concentrations (1.88 ppbv ethane, 0.092 ppbv propene, 0.398 ppbv propane, 0.063 ppbv isobutene, 0.075 ppbv n-butane, 0.106 ppbv benzene, 0.102 ppbv toluene) observed on a flight to the west of Bermuda on April 28 (alt. 4100 m) indicated upwardly lifting convective activity of continentally sourced air masses. A meteorologically informed sampling strategy employed in the study was valuable in providing a framework with which to both optimize NMHC sampling decisions and to provide a context with which to interpret their observed mixing ratios.