{"id":79,"date":"2016-03-22T17:29:11","date_gmt":"2016-03-22T17:29:11","guid":{"rendered":"http:\/\/newvista.cira.colostate.edu\/Improve\/?page_id=79"},"modified":"2026-08-13T20:11:15","modified_gmt":"2026-08-13T20:11:15","slug":"the-improve-algorithm","status":"publish","type":"page","link":"https:\/\/vista.cira.colostate.edu\/Improve\/the-improve-algorithm\/","title":{"rendered":"The IMPROVE Algorithm"},"content":{"rendered":"\n

The IMPROVE algorithm for estimating light extinction was adopted by the U.S. Environmental Protection Agency (EPA) as the basis for the regional haze metric used to track progress in reducing haze levels for visibility protected areas under the 1999 Regional Haze Rule (RHR).  The RHR uses the IMPROVE algorithm to estimate light extinction, which is then converted to the deciview haze index.<\/p>\n\n\n\n

The First IMPROVE Equation<\/em><\/strong><\/p>\n\n\n\n

The IMPROVE algorithm was originally developed by Malm et al., <\/em>1994.\u00a0 This algorithm, often referred to as the IMPROVE Equation, is based on the assumptions that absorption by gases (ba,g<\/sub>) is zero, that Rayleigh scattering (bs,g<\/sub>) is 10 Mm-1<\/sup> for each monitoring site, and that particle scattering and absorption (bs,p<\/sub> and ba,p<\/sub>) can be estimated by multiplying the concentrations of each of six major components by typical component-specific mass extinction efficiencies.\u00a0 The sulfate and nitrate mass extinction efficiency terms include a water growth factor that is a function of RH (displayed as f(RH)) multiplied by a constant dry extinction efficiency.<\/p>\n\n\n\n

b<\/em>ext<\/sub>  \u2248  3 \u00d7 f<\/em>(RH<\/em>) \u00d7 [Ammonium Sulfate<\/em>] + 3 \u00d7 f<\/em>(RH<\/em>) \u00d7 [Ammonium Nitrate<\/em>] +<\/p>\n\n\n\n

4 \u00d7 [Organic Mass<\/em>] + 10 \u00d7 [Elemental Carbon<\/em>] + 1 \u00d7 [Fine Soil<\/em>] + 0.6 \u00d7 [Coarse Mass<\/em>]<\/p>\n\n\n\n

+ Rayleigh scattering<\/em><\/p>\n\n\n\n

where light extinction and Rayleigh scattering (10 Mm-1<\/sup>) are given in inverse megameters (Mm\u20111<\/sup>); concentrations shown in brackets are in microgram per meter cubed (\u03bcg m-3<\/sup>); dry mass extinction efficiency terms are in units of meters squared per gram (m2<\/sup> g-1<\/sup>); and the water growth terms, f(RH), are unitless.<\/p>\n\n\n\n

fRHOriginalIMPROVE.csv<\/a><\/u><\/strong>  f(RH) values for calculating light extinction from IMPROVE data using the Original IMPROVE Equation.<\/p>\n\n\n\n

IMPROVE_site_frh_2025.csv<\/u><\/strong> <\/a> Because many monitoring sites do not include on-site RH monitoring, monthly averaged water growth terms for each site were developed for RHR calculations.   Monthly values for the first IMPROVE equation are given as \u2018frh\u2019 (columns AN-AY).<\/p>\n\n\n\n

The Second IMPROVE Equation<\/em><\/strong><\/p>\n\n\n\n

The first IMPROVE algorithm performed reasonably well; however, it tended to underestimate the highest extinction values and to overestimate the lowest extinction values.  As such, a revised algorithm was developed by Pitchford et al.<\/em>, 2007.  Like the first IMPROVE equation, the revised algorithm is relatively simple, it produces consistent estimates of light extinction for all remote-area IMPROVE aerosol monitoring sites, and it permits the individual particle component contributions to light extinction to be separately estimated.  Five major revisions were made to the original IMPROVE algorithm for estimating light extinction from IMPROVE particle speciation data. They include:<\/p>\n\n\n\n