Long Term Trends

The long term trends (1988 - 1998) of fine mass and its major aerosol types and light extinction and the contribution of major aerosol types to light scattering for each IMPROVE monitoring site with data since 1988.

These trends were generated using the procedures from the Draft Guidance for Tracking Progress Under the Regional Haze Rule. The SO4 ion data were used to replace all potentially biased sulfur data.  Constant group 10, 50 and 90 ammonium nitrate value were used in all calculations.  The ammonium nitrate values were calculated from the 1997-99 data.  This was done to remove the potential bias in pre 1996 nitrate data.  It is anticipated that the EPA methodologies will be different and these figures will be updated after the EPA methods are finalized.  See  the IMPROVE Data QA/QC Issues page for more information on the biased sulfur and nitrate data. 

See the Tools and Algorithm section for a description of the variables and how they are derived from the speciated aerosol data.