The 1999 Regional Haze Rule provides a context for this review of visibility, the science that describes it, and the use of that science in regulatory guidance The scientific basis for the 1999 regulation is adequate The deciview metric that tracks progress is an imperfect but objective measure of what people see near the prevailing visual range The definition of natural visibility conditions is adequate for current planning, but it will need to be refined as visibility improves Emissions from other countries will set achievable levels above those produced by natural sources Some natural events, notably dust storms and wildfires, are episodic and cannot be represented by annual average background values or emission estimates Sulfur dioxide (SO2) emission reductions correspond with lower sulfate (SO4 2−) concentrations and visibility im-provements in the regions where these have occurred Non-road emissions have been growing more rapidly than emissions from other sources, which have remained

Visibility: Science and Regulation

Multiple linkages connect air quality and climate change. Many air pollutant sources also emit carbon dioxide (CO2), the dominant anthropogenic greenhouse gas (GHG). The two main contributors to non-attainment of U.S. ambient air quality standards, ozone (O3) and particulate matter (PM), interact with radiation, forcing climate change. PM warms by absorbing sunlight (e.g., black carbon) or cools by scattering sunlight (e.g., sulfates) and interacts with clouds; these radiative and microphysical interactions can induce changes in precipitation and regional circulation patterns. Climate change is expected to degrade air quality in many polluted regions by changing air pollution meteorology (ventilation and dilution), precipitation and other removal processes, and by triggering some amplifying responses in atmospheric chemistry and in anthropogenic and natural sources. Together, these processes shape distributions and extreme episodes of O3 and PM. Global modeling indicates that as air pollution programs red...

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Air quality and climate connections.

Sample preparation for chromatographic separations: an overview

Analytical techniques for the determination of total sulfates in diesel particulates are described utilizing the techniques of total combustion/nondispersive infrared (NDIR) detection and modified extraction/barium perchlorate-thorin titration (BPT). The combustion technique utilizes a commercially available sulfur analyzer (LECO-IR32) that requires less than 15 min for triplicate analysis and has a precision and accuracy of better than +- 5% for filter samples containing from 100 to 10,000 ..mu..g of sulfate. The combustion technique measures soluble and insoluble sulfate such as BaSO/sub 4/ and is not affected by the presence of large quantities of carbon in the particulate sample. The extraction efficiency for sulfates in diesel particulates using standard procedures was found to average 67% for samples containing only trace quantities of anions and 59% for samples containing stoichiometric levels of barium. These procedures have been modified to include ultrasonication with 2-proponal/water in order to overcome the problem of incomplete sulfate extraction. Extracted sulfate samples are then analyzed by using the BPT method. The extraction/BPT method showed an average recovery of 1.02 +- 0.12 (1 sigma) when compared to the combustion technique. ESCA studies showed that the chemical state of the surface sulfur species for the diesel particulates average 93 +- 3%more » sulfate and 7 +- 3% elemental sulfur.« less

Determination of sulfates in diesel particulates

Toxic air pollutants — assessing their importance

Literature concerning analysis of air contaminants has increased rapidly in recent years. EPA, Intersociety Committee, and ASTM reference methods are summarized. The validity of using data obtained with high volume samplers and gas absorption bubblers in sampling networks, using part-time operators, to determine base-line levels and air quality assurance is questioned. Dichotomous or size classification samplers for respirable particulates provide more accurate data to assess health effects. Described are: improved methods using particulate sulfates to determine the composition and effects of acid rain; new techniques for determining the composition of aerosol contaminants and measuring toxic gases, including coupled gas chromatography-mass spectrometry, X-ray fluorescence, and proton induced X-ray emission; and remote sensing methods involving correlation spectrometry, tunable lasers, and differential lidar. (275 references, 9 tables)

Katz M

Papers

Advances in the analysis of air contaminants: a critical review