This dataset contains the measured (“raw”) aerosol data from the IMPROVE monitoring network, which collects 24 hour PM2.5 and PM10 samples every third day at over 150 sites.  The PM2.5 samples are analyzed for mass, elemental species, elemental and organic carbon, and selected ions, while the PM10 samples are analyzed for mass. These data are used in a number of ways and are instrumental in supporting the implementation of the Regional Haze Rule (RHR), though the RHR metrics and methods are explicitly incorporated in the RHR1 and RHR2 versions of the data. The IMPROVE dataset is under constant analysis and new data are routinely added every three months. The current dataset is archived in January of each year, and any corrections or data-processing improvements are subsequently applied.

This dataset contains the newest IMPROVE Aerosol data that have been released by the IMPROVE Air Quality Group at CNL. These data are considered “preliminary” for an informal review period of approximately one to two months, during which the data are further examined for issues or errors. During the review period, incomplete and unverified data are frequently posted for exploratory use. As an example, carbon concentrations will often be released before elemental and ion concentrations are available. Once the review period has passed and any identified errors have been corrected, the data are transferred to the primary IMPROVE Aerosol dataset (see IMPROVE Aerosol).

This dataset contains composite aerosol concentrations and their individual contributions to light extinction in addition to haze metrics for each valid IMPROVE sample and various data aggregations. It also includes a “group” parameter which indicates if a given data point occurs within the set of 20% “best” or 20% “worst” visibility days in a given year. This dataset is derived by applying the procedures described in the RHR document “Guidance for Tracking Progress under the Regional Haze Rule (Sept. 2003)” to the IMPROVE Aerosol dataset. Any missing values are “patched” according to the guidance document and appropriately flagged. Because these data are used to support the RHR and have regulatory significance, all data in the RHR baseline period from 2000-2004 are considered “frozen” and will not be changed to correct small errors that may be discovered in the raw IMPROVE data. Therefore, these data may not be completely reproducible from the current data in the IMPROVE aerosol dataset. (NOTE: This dataset does not contain any “substituted” data provided by various States to fill in additional missing values.)

This dataset is similar to the RHR1 dataset, but uses the revised IMPROVE algorithm for estimating light extinction and excludes the major aerosol species concentrations. In the revised algorithm, total sulfate, nitrate and organic carbon compound concentrations are each split into two fractions, representing small and large size distributions of those components. The organic mass concentration used in the new algorithm is 1.8 times the organic carbon mass concentration, changed from 1.4 times carbon mass concentration as used in the original algorithm. Sea salt and its associated extinction value has been added, as well as climatological f(RH) and f(RH) for the small and large aerosol fractions. Site-specific Rayleigh scattering is calculated for the elevation and annual average temperature of each IMPROVE monitoring site. In addition, “substituted” data supplied by individual States to fill in missing concentration values have been included, where available. In some cases, the inclusion of these substituted data results in a different “group” value (which indicates if a given data point occurs within the set of 20% “best” or 20% “worst” visibility days in a given year) than would be indicated otherwise. As with the RHR1 dataset, this dataset has regulatory implications and will not be changed to correct small errors that may be discovered in the raw IMPROVE data. Therefore, these data may not be completely reproducible from the current data in the IMPROVE aerosol dataset.

An IMPROVE monitoring site can have missing data for various reasons, e.g. a power outage at the monitoring site. In some instances, there is enough missing data that the monitoring site fails the completeness criteria to calculate a valid haze metric for the Regional Haze Rule (RHR) baseline period (2000 - 2004). The RHR guidance documents describe procedures for filling in some missing values with “patched” data. However, the criteria to fill in a missing value are strict and few values are actually filled in. A number of States have developed different procedures to fill in missing values and have submitted these data to the VIEWS database. These data are referred to as “substituted” data in order to differentiate them from the RHR “patched” data. Currently substituted data are available from 19 monitoring sites. These sites were selected because they either did not have the required 3 years of valid data to calculate the RHR haze metrics for the baseline period or they did not have complete data for the year 2002 (which serves as the primary modeling year for the Regional Planning Organizations) and monitoring data was needed to evaluate and use the modeling results. This list of sites and substituted data procedures are available from the Substituted Data Page. These data are also available from the VIEWS Query Wizard by selecting the IMPROVE Aerosol, RHR2 network.

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The IMPROVE program as well as a number of State and federal organizations operate Optec NGN-2 open air integrating nephelometers to measure the light scattering coefficient every hour at a number of primarily remote sites. Data has been collected at over 60 monitoring sites for various lengths of time as early as 1992. A number of nephelometers are in operation today, but the number of sites changes yearly. These data are available as ascii files from the IMPROVE Optical Data Page. They can also be obtained from the VIEWS Query Wizard. The data are updated every quarter with an approximately six month delay.

The IMPROVE program operated Optec Model LPV-2 long path visibility transmissometers to measure total light extinction every hour at 18 Class I Areas over varying lengths of time. The first transmissometer began operating in 1986 on the rim of the Grand Canyon NP. In 2007, operation of all transmissometers for collecting quality control data was discontinued. These data are available only in ascii files from the IMPROVE Optical Data Page.