Data Mining to Determine Local Effects of MercuryEmissions

摘要

Tools for knowledge discovery through databases (KDD) can provide air quality planners withdescriptions of long-term behavior at monitor sites. The investigators used the Cubist? programto construct a piecewise linear regression model to describe mercury deposition rates andconcentrations at two sites in terms of hourly power plant heat input (a surrogate for emissions)and meteorological variables. The ambient mercury measurements represented more than fiveyears of data at the Marcell, Minnesota and Chassahowitzka, Florida sites of the MercuryDeposition Network. The daily heat input data represented two power plants (Boswell EnergyCenter and Florida Power’s Crystal River Energy Complex) that are predominantly coal-fired.The advantages of local versus regional controls for mercury emissions have recently beendebated. This work aimed to identify the meteorological conditions that lead to an effect of localemissions on local ambient mercury conditions. The long time series of ambient mercurydeposition data at Marcell, Minnesota and Chassahowitzka, Florida were compared with thesimultaneous heat input quantities at the two nearby power plants.Meteorological conditions were included in the data sets, and the Cubist software generatedpiecewise linear regression fits that describe the deposition data based on heat input andmeteorological parameters. The software created models of several linear expressions that applyunder particular meteorological conditions and sometimes overlap. The investigation showedthat the effect of power plants on nearby mercury deposition sites only manifested itself underparticular meteorological conditions. The data analyses and findings are discussed in detail.The investigation pointed to a rise in mercury deposition at the Marcell site associated with rateincreases in heat input at the Boswell Energy Center, likely occurring during boiler startup orshutdown. The spikes above the average deposition represent only eight percent of the weeklydata at Marcell but forty-two percent of the total deposition. During hot, stagnant conditions,Crystal River heat input rates sometimes affected mercury concentrations and deposition at theChasshowitzka station (0.038 ng-hr/l-mmBtu).