Maps of PM2.5 over the U.S. Derived from Regional PM2.5 and Surrogate

Visibility and PM10 Monitoring Data

Stefan R. Falke and Rudolf B. HusarCenter for Air Pollution Impact and Trend Analysis

Washington University St. Louis, Missouri

Overview

•Fine mass (particulate matter <2.5 µm in diameter) is currently monitored at a limited number of locations.

•Incorporation of related data into the spatial interpolation of fine mass aids the interpolation. This paper describes the methodology used in deriving fine particle maps for the U.S. by using visibility (280 sites) and PM10 data (~1000 sites) as fine mass surrogates.

•The higher resolution spatial coverage of the visibility and PM10 networks combined with their relationships to fine mass results in more detailed fine mass maps.

• Quarterly fine mass maps are derived for 1988-92.

Fine Mass Monitoring Network Visibility Monitoring Network

Surrogates for Fine Mass Concentrations

PM10 Monitoring Network Fine Mass vs. Visibility

Fine Mass Concentrations1/r2 Interpolation

Extinction Coefficient1/r2 Interpolation

BextFine Mass1/r2 Interpolation

Bext Aided FM = Fine Mass Bext

x Bext

Surrogate Aided Interpolation

Fine mass concentrations from the IMPROVE and NESCAUM networks, 1988-1992.

Sparse site coverage, ~50 sites located mostly in rural areas results in coarse spatial pattern.

75th percentile visibility extinction coefficient, 1988-1992

High spatial resolution visibility observation network

(~280 monitoring sites)

Fine Mass using Bext Surrogate

Before After

Before After

Fine Mass using Bext Surrogate

Fine mass from IMPROVE/NESCAUM and AIRS 1988-1992

AIRS PM10 Concentrations, 1988-1992

AIRS consists of mostly urban monitoring sites. Using these as surrogates would result biased regional PM2.5 estimates.

‘Regional’ AIRS PM10 concentrations

Monitoring sites with PM10 concentrations below a ‘base’ level were considered regional.

Fine Mass using PM10 Surrogate

Before After

Fine Mass using PM10 Surrogate

Before After

Correlation coefficients (R2) for interpolation error tests

Quarter Measured vs.ReconstructedConcentration

CrossValidation

using 1/r2 (nosurrogate)

Cross Validationusing 1/r2 with

Surrogate

Fine Mass & Q1 0.99 0.61 0.64

Visibility Q3 0.99 0.86 0.89

Fine Mass & Q1 0.94 0.00 0.12

PM10 Q3 0.98 0.59 0.69

Conclusions

• Derived fine mass maps using surrogates were of higher spatial resolution.

• Locations with observed fine mass concentrations remained unchanged by the surrogates.

• Cross validation analysis indicates improvement with the surrogates

• Visibility performs better than PM10

• Future work will merge Visibility and PM10.

Methodology

1. Use high spatial resolution surrogate monitoring sites to interpolate a surrogate grid.

2. Obtain a surrogate value at each of the fine mass monitoring sites

3. Calculate the FM/Surrogate ratio at each of the fine mass monitoring sites

4. Interpolate the FM/Surrogate ratio to a grid

5. FM/Surrogate * Surrogate = FM Grid

Bext to Fine Mass Ratios

A spatially smooth pattern with exceptions over northern Minnesota, eastern California and southern Oregon.

Fine mass ratio.