Revised Algorithm for Estimating Light Extinction from IMPROVE Particle Speciation Data

Abstract

The Interagency Monitoring of Protected Visual Environments (IMPROVE) particle monitoring network consists of approximately 160 sites at which fine particulate matter (PM2.5) mass and major species concentrations and course particulate matter (PM10) mass concentrations are determined by analysis of 24-hr duration sampling conducted on a 1-day-in-3 schedule A simple algorithm to estimate light extinction from the measured species concentrations was incorporated in the 1999 Regional Haze Rule as the basis for the haze metric used to track haze trends. A revised algorithm was developed that is more consistent with the recent atmospheric aerosol literature and reduces bias for high and low light extinction extremes. The revised algorithm differs from the original algorithm in having a term for estimating sea salt light scattering from Cl(-) ion data, using 1.8 instead of 1.4 for the mean ratio of organic mass to measured organic carbon, using site-specific Rayleigh scattering based on site elevation and mean temperature, employing a split component extinction efficiency associated with large and small size mode sulfate, nitrate and organic mass species, and adding a term for nitrogen dioxide (NO2) absorption for sites with NO2 concentration information. Light scattering estimates using the original and the revised algorithms are compared with nephelometer measurements at 21 IMPROVE monitoring sites. The revised algorithm reduces the underprediction of high haze periods and the overprediction of low haze periods compared with the performance of the original algorithm. This is most apparent at the hazier monitoring sites in the eastern United States. For each site, the PM10 composition for days selected as the best 20% and the worst 20% haze condition days are nearly identical regardless of whether the basis of selection was light scattering from the original or revised algorithms, or from nephelometer-measured light scattering.

A critical review of filter transmittance measurements for aerosol light absorption, and de novo calibration for a decade of monitoring on PTFE membranes

“…Throwing all ten years of data into the same regression yields the coefficients A D 10:2 m 2 6 gEC and B D 6:6m 2 6 gFe for an overall relationship that explains a little over one third (r 2 D 0.36) of the observed variance in Fabs 6 EC. The intercept A, an estimate for the MAC of EC in the absence of dust, is statistically indistinguishable from the reference value Fabs 6 EC D 10 m 2 6 g that is traditionally assumed in IMPROVE-based extinction estimates (Malm et al 1994, Pitchford et al 2007). This is significantly higher than the wavelengthadjusted MAC of 6:5 D 7:5£ 550 633 that recommend for freshly generated carbon soot.…”

Changes in visibility with PM2.5 composition and relative humidity at a background site in the Pearl River Delta region

“…The hygroscopic growth factor f(RH) for AS and AN, and f(RH) ss for SS were obtained from the tabulated values in Malm et al (1994) and Pitchford et al (2007), respectively. Rayleigh scattering (~10/Mm) was negligible and hence not included in the equation (IMPROVE Report V, 2011).…”

Characteristics of Mass Absorption Efficiency of Elemental Carbon in Urban Chengdu, Southwest China: Implication for the Coating Effects on Aerosol Absorption

“…Moreover, aerosol light absorption coefficient in Chengdu was higher than those in other megacities of China (such as Beijing, Xi'an, Shanghai and Guangzhou) (Cao et al 2012;Jing et al 2015;Tao et al 2014b;Wu et al 2009;Zha et al 2014). Furthermore, the MAEs of EC at 550 nm in Chengdu were even higher than 10 m 2 g −1 recommended by the IMPROVE formula (Pitchford et al 2007;Tao et al 2014b). Until now, only few studies have investigated the reasons why the MAE of EC was so high there (Tao et al 2014b).…”