IMPROVE Gray Literature

The proposed new algorithm described in this report was adopted for use by the IMPROVE Steering Committee in December 2005.

ABSTRACT: In this study, a statistical method known as Positive Matrix Factorization (PMF) was used to analyze IMPROVE monitoring data collected at two west coast Class I areas over two time periods, 1991-1995 and 2000-2003. These Class I areas were Mt. Rainier National Park in Washington, and Yosemite National Park in California. PMF generated source profiles associated with each source of fine particulates, and generated a time-dependent series of fine particulate concentrations from each source in these two Class I areas. The light extinction of each source was determined by summing the light extinction of all the light absorbing chemical species in each source. The average light extinction of each source for 1991-1995 and 2000-2003 were summed to determine the total light extinction in each Class I area for these time periods. The total light extinction in each Class I area in 2002 was also determined for the worst 20% visibility days, which is one of the parameters identified in EPA’s Regional Haze Rule to determine progress towards improving visibility in Class I areas.  The composition of the biomass source in Yosemite was also examined to determine the relative contribution of fine particulates from biomass combustion and biogenic emissions to visibility impairment on the 20% worst visibility days in 2002. The results show that PMF can be used as a tool to help determine which sources have the most significant impact on visibility in Class I areas, and how the visibility impairment from each source varies over time.

This paper uses Lorenz-Mie theory, reasonable estimates of the variation of ambient aerosol properties, and the optical characteristics of currently available nephelometers and light scattering photometers to investigate the theoretical limits of the accuracy and precision of PM2.5 mass measurements estimated by nephelometry.

The integrating nephelometer directly measures the scattering coefficient of atmospheric aerosols. The Optec NGN integrating nephelometer was designed to operate in low power, low maintenance, and ambient field conditions. This required two main compromises in the optical design:

· The use of a photodiode rather than a photomultiplier tube (PMT) detector, and

· A wide band filter to compensate for the reduced sensitivity of the photodiode compared to a PMT.

The following is a theoretical examination of the effect of these design requirements on the measurement accuracy of the Optec NGN integrating nephelometer and an experimental determination of the measurement precision of the instrument. Included in the theoretical analysis are comparisons to three other currently available integrating nephelometers:

· TSI 3563: TSI, Inc., St. Paul, Minnesota

· Belfort 1590 : Belfort Instrument Company, Baltimore, Maryland

· Radiance Research M903: Radiance Research Inc., Seattle, Washington

This report summarizes Air Resources Specialists' (ARS) operational experience with the Optec Next Generation Nephelometer (NGN) from 1992 to 1994.  It describes several design, manufacturing and operating deficiencies that were discovered and instrument upgrades to address these deficiencies.

The DRI/OGC analyzers used for IMPROVE carbon analysis since 1987 are obsolete and spare parts for repairs are no longer manufactured and increasingly difficult to obtain.   The Model 2001 carbon analyzer has been designed and tested as a replacement for future IMPROVE sample analysis.  This report summarizes a number of analyses comparing the DRI/OGC and Model 2001 analyzers under different configurations.  The similarities and differences are reported and recommendations are made for a smooth transition from the current DRI/OGC analyzer to the Model 2001. 

A power point presentation on the assessment of the comparability between the current DRI/OGC carbon analyzer used in IMPROVE and the new Model 2001 carbon analyzer proposed as the DRI/OGC replacement.

Positive Matrix Factorization (PMF) was used to model IMPROVE monitoring data collected at the Mt. Zion and Wishram monitoring sites in the Columbia River Gorge National Scenic Area. PMF was able to identify source categories that contribute to the fine particulates (PM2.5) measured at each site, the average percent PM2.5 mass allocation from each source category, and the time-dependent allocation from each source category. PMF identified 9 source categories for the Mt. Zion site based on 1996-98 data, and, 9 source categories for the Wishram site based on 1993-95 data.

A presentation describing the IMPROVE particulate monitoring network and the spatial and seasonal patterns of the composite aerosol components from all data collected in 2001.  Some results from IMPROVE special studies are also included.  The was presented at the Science Colloquium on Measuring and modeling aerosols, June 14-16 in Baltimore, MD. Many of the figures of the particulate patterns can be found in the paper Malm et al., 2004, J. of Geo. Res. Vol 109, D03306

Describes some of the limitations and issue concerning the transmissometer data and problems with using the long-term transmissometer records for trend analysis.

Reconstructed mass excluding nitrate is compared with gravimetric mass for each year of the IMPROVE network.  Two parameters were used to investigate the trends.  The first is the slope of the regression line through the origin, assuming gravimetric mass is independent.  The second is the ratio of the two means.  The slope emphasizes points with large mass, while the ratio reflects the average samples.  No significant historical trends in the difference between the measured and reconstructed fine mass was found.

An Explanation as to why Na is multiplied by a factor of 2.5 to reconstructed sea salt.

In 1999 the IMPROVE network began to expand to monitor visibility in all Class I areas that visibility was deemed an important attribute of the Area.  This document describes the procedure used to select the new IMPROVE monitoring sites.

A 1995 report providing an overview of the IMPROVE network.  This document describes the IMPROVE monitors and filter analysis, estimation of uncertainty in the measures species, calculation of the major aerosol types and their uncertainty, as well as the effect of changing the analysis from PIXE to XRF for elements between Fe and Pb on the minimum detection limits and precision.

A document containing images representing the cleanest and the haziest clear sky, non-weather, days found in the IMPROVE 35mm slide data base. Extinction coefficient estimates are also provided based upon the slide contrast measurements, the average species concentrations of the 20% lowest and highest fine mass days, and annual estimates of the f(rh).

Examination and estimation of uncertainties in light extinction derived from apparent contrast measurements from images of natural targets.

This document summarize the limitations and value of light extinction and visual range measurements from slide based images.

This report analyzes the sampling completeness for the IMPROVE aerosol monitoring network in 2001.  It was found that the median site had a 92% completion rate, which is excellent.  Ninety percent of the sites had a completion rate greater than 75%, which is the annual criterion for acceptance.  If we consider only the 103 sites were installed before January 2001, then 12 failed the annual criterion and 3 others failed the quarter or 10-consecutive criteria. 

The IMPROVE denuder has a collection efficiency for SO₂ of >99% when freshly coated.  There is some question about whether there is breakthrough of SO₂ and HNO₃ after being used for a year, at least at sites with high SO₂ concentrations.  This report examines the effect of breakthrough of SO₂ on the sulfate measurements and of HNO₃ on the nitrate measurements. 

The primary purpose of flow control is to keep the volume flow rate through the cyclone or PM₁₀ inlet as close as possible to the nominal rate for the 2.5 or 10 µm cut.   There are several factors producing a variation in the flow rate for a critical orifice:  the diurnal and seasonal variation of ambient temperature, the change in pressure drop across the filter associated with variation in clean filters, and the change in pressure drop across the filter associated with mass loading.  The estimated total variation in inlet flow rate with a critical orifice controller from all three factors is generally less than 3%.  This is similar to the standard deviation in flow rates observed in the network.  The conclusion is that a critical orifice system is reasonable if a variation in flow rate of approximately 3% is acceptable.

Long term trends in the EC/OC ratios in the IMPROVE network have been found.  This report examines the question as to whether these trends are real or caused by analytical changes in the IMPROVE network.  In addition, the appendix examines the seasonal variation and long term trends in the organic and elemental carbon artifacts.

Significant changes were made in the IMPROVE cassettes in the new version of the sampler installed in the year 2000.  The Version 2 cassette sampler are made of an inert plastic, Delrin®, and the filters sit on stainless steel screens.  The Version 1 cassettes were  polycarbonate and sat on cellulose drain discs over polycarbonate support grids.  This report examines the change in the organic and elemental carbon artifact after the Version 2 cassettes were installed.

Warren White noted a trend in the ratio of nylon sulfate / Teflon sulfur over the course of the IMPROVE network.  This is extremely critical in determining sulfate trends.  This report concludes that there is no trend in the ratio of analytical calibrations, but there is a trend in the relationship at low concentrations.  This is seen in the intercept and in distributions.  The low end concentrations are primarily affected by the artifact that is subtracted from the samples.  This change in low end concentrations can account for the trend in the ratios.  No mechanism for producing such a change has been identified.

This report details the changes in the sampling and filter analysis in the IMPROVE program that could affect the fine particle sulfur or sulfate measurements.  It was found that three issues could produce invalid data and the possible impact of these issue is examined using eastern US data.  

The IMPROVE (Interagency Monitoring of Protected Visual Environments) network collects PM_2.5 particles on Teflon, nylon, and quartz filters using a modular, cyclone-based sampler with critical orifice flow control.  Understanding the protocols of IMPROVE is important because IMPROVE will continue to provide background monitoring at Class I areas, and because the protocols for measuring chemical species in the Federal Reference Method network at urban and suburban sites will probably be similar.  The IMPROVE filters are analyzed by seven methods to obtain concentrations of mass, elements H and Na-Pb, ions NO₃^- and SO₄⁼, organic and elemental carbon, and the coefficient of absorption.  The replicate precision for most analytical methods is approximately 4%.  The artifacts for all methods except carbon are small or zero.  The artifact problem for organic carbon is minimized by allowing each filter to reach saturation prior to collection.  Redundant measurements by the three filters permit improved quality control.  Comparisons of sulfur with sulfate and organic carbon with organic hydrogen permit assurance that (1) the calculated uncertainties are reasonable, (2) the analytical methods are correctly calibrated, (3) the flow rates of the various modules are in agreement, and (4) the individual concentrations are valid.

This paper examines the annual and seasonal spatial patterns of the major aerosol components (sulfate, nitrate, organics, elemental carbon (EC), and soil) from the IMPROVE monitoring network.  The data were from 70 monitoring sites with one year of data from March 1996 through February 1998.

The Model LPV-2 Long Path Visibility Transmissometer consists of a constant output light source transmitter and a computer controlled photometer     receiver. The irradiance at 550nm wavelength from the transmitter can be measured to a high degree of accuracy both day and night, and over a path length of up to 15 km depending on expected extinction values. Both the receiver and transmitter operate from a 12 volt battery source and use 5 and 34 watts respectively. The signal is processed by an internal CMOS 8-bit computer and the output voltage can made proportional to extinction or visual range. The units can operate for long periods of time unattended in a continuous or timed cycle mode. The self resetting and battery backup systems ensure continued operation even after power blackouts and computer lockup due to local static electric discharges. Both units can be synchronized, programmed and calibrated at the home station and installed in the field ready for operation.

The Model NGN-2 (Next Generation Nephelometer) uses a unique integrating open-air design that allows accurate measurement of the scattering extinction coefficient of ambient air. Because of the open-air design, relative humidity and temperature of the air sample are essentially unchanged, thus the aerosol is negligibly modified when brought into the optical measuring chamber. With improvements made to the prototype NGN-1, the production Model NGN-2 nephelometer alters the temperature of the air sample by less than 0.5° C. Extinction due to scatter can accurately be measured from Rayleigh to 100% saturated fog conditions. Using principals and techniques developed for the popular and successful Optec LPV transmissometer, the NGN-2 features low power consumption, solid compact design, and easy operation - all necessary parameters when installing and operating a measuring instrument in remote locations. Housed in a single environmentally sealed enclosure, the nephelometer contains all the necessary components for ambient standalone operation. The NGN-2 consists of a large inlet with motorized door, measuring chamber, clean air pump for calibration, blower, solenoid activated inlet for a span gas, temperature sensor, real time clock and rain detector for closing the inlet during wet conditions. See Figure 1-2 for a cross-sectional view of the NGN-2. A CMOS computer controls all operating functions and outputs data either in digital or analog format. External to the NGN-2 unit, a 13.8V DC, 5 amp power supply, compressed span gas and a data logger or printer are required.