Under the 1980 visibility regulation, source attribution analyses may be required for Class I areas where it is believed that one or more sources substantially contribute to visibility impairment. When routine monitoring data are insufficient for the attribution analysis, special studies may be performed. These studies are designed to obtain the necessary air quality, meteorological, and emission data to identify the sources contributing to visibility impairment and their frequency, duration, and contribution to visibility impairment. In addition to source attribution, special studies have been performed to enhance the science of visibility monitoring and learn about aerosol physio-chemical-optical properties. Several of the studies listed below have been conducted independent of the IMPROVE program
Reductions in haze across the United States since the early 1990s Visualized using WinHaze Simulated Photographs - The effects of the changes in the 20% haziest days on the scene for ~50 national parks and wilderness were simulated using WinHaze. The haziest reconstructed bext values corresponding to the beginning and end of trend periods for each site as estimated using IMPROVE data were input into WinHaze to visualize the changes in the scene.
Apportionment of Biomass Burning Contribution to Haze and PM2.5 - This project was designed to develop better tools to apportion the contributions of biomass burning from different fire types, e.g. wildfires and prescribed fires to PM2.5 and haze. As part of this study a retrospective hybrid-receptor model based on the positive matrix factorization (PMF) model was developed. The project was partially funded by the Joint Fire Science Program.
IMPROVE Coarse Mass Speciation Study - To more fully investigate the composition of coarse particles, a program of coarse particle sampling and speciation analysis at nine of the IMPROVE sites was initiated between 19 March 2003 and 23 December 2003, with each site operating for one year.
Yosemite Aerosol Characterization Study - The Yosemite Aerosol Characterization Study (YACS) was an intensive field measurement campaign conducted by a number of U.S. research groups from 15 July to 4 September 2002 at Yosemite National Park (NP), California.
Big Bend Regional Aerosol and Visibility Observational Study (BRAVO) - The BRAVO study is designed to investigate the causes of haze at the Big Bend National Park. The network operated from July to October, 1999 measuring fine aerosol mass and its constituents, atmospheric optical properties, gaseous air pollutants and meteorology at Big Bend.
Southeastern Aerosol and Visibility Study (SEAVS) - This study measured aerosols under humid Southeastern US conditions to determine the contribution of major aerosol constituents, including water, to the total particle mass and light extinction. Field measurements included particle size, water and optics, aerosol composition, meteorology and human perception of scenes at the Great Smoky Mountains National Park over a 6 week period during the summer of 1995.
Measurement of Haze and Visual Effects (MOHAVE) - This network was established to help determine the contributions of the Mohave Power Plant and other sources to haze at Class I areas in the Southwestern US. The MOHAVE network employed 43 IMPROVE type samplers in the Southwest collecting daily particulate samples over a 24 hour period. The network collected data over a winter and summer period from 1/10/–2/15/92 and 7/11/–9/2/92 respectively. The particulate samples were analyzed for PM2.5 and its elemental constituents, organics, ions, light absorption and PM10.
The Pacific Northwest Regional Visibility Experiment Using Natural Tracers (PREVENT) - This network was established to study visibility causes and effects in Washington state, west of the Cascades. The network consisted of 34 monitors located in Washington and Oregon. Daily particulate samples were collected from 6/90–9/90 and analyzed for PM2.5 mass and its elemental constituents and light absorption.
The Winter Haze Intensive Tracer Experiment (WHITEX) - This study was established to study the visibility impacts of emissions from the Navajo Generating Station. The database contains data from 13 locations which sampled from 1/1/87 – 2/18/87. Samples were collected every 6, 12, and 24 hours depending on the site and sampler. The particulate samples were analyzed for PM2.5 mass and its elemental constituents, organics, ions, and light absorption.
The Mt. Zirkel Visibility Study (MZVS) - A visibility study designed to determine the extent of visibility impairment at the Mt. Zirkel Wilderness Area and contribution of the major sources responsible for any visibility impairment.
The Navajo Generating Station Visibility Study (NGS) - The NGS Visibility Study was conducted by the SRP, the operators of NGS, from January 10 through March 31, 1990. Its purpose was to address visibility impairment in Grand Canyon National Park during the winter months and the levels of improvement that might be achieved if SO2 emissions from NGS were reduced. The study was performed to provide input to the rulemaking process of the EPA regarding NGS SO2 controls. Perfluorocarbon tracers (PFT) were released from the three stacks of NGS. Surface and upper air meteorology, particle and gaseous components, and tracer were measured at many sites. The study concluded that the NGS plume was not present at Hopi Point for most of the days. The tracer data quality from this experiment was insufficient for quantitative source apportionment and the results emphasized the need for better tracer measurements in future studies.