VISIBILITY ANALYSIS RECOMMENDATIONS FEDERAL LAND MANAGERS’ AIR QUALITY RELATED VALUES WORKGROUP

“…methods for analyzing the impacts on visibility from new or modified air pollution sources.”

REGULATORY BASIS FOR RECOMMENDATION National Goal (Clean Air Act Section 169A) –Sets goal as no manmade impairment Definition of Visibility Impairment (40 CFR § (x)) –Sets natural conditions as the benchmark

COMPONENTS OF THE RECOMMENDATION Analysis Methodology (including a prescriptive outline) Class I Area Specific Information Identifies Thresholds –levels of concern –analysis thresholds –decision thresholds Sample Application

FUNDAMENTAL PRINCIPLE New Sources (PSD and those subject to new source review) should not, by themselves, significantly impede progress toward the national visibility goal

METHODOLOGY PROTOCOLS Discrete Plumes (Near Field) –Sources within 50 km of the Class I Area –Visibility parameters contrast color difference (delta E) –Natural conditions as benchmark –VISCREEN, PLUVUE II

PROTOCOLS (CONTINUED) Aggregates of Discrete Plumes (Distant/multi-source) –Multiple Sources or Greater than 50 km from Class I Area –Visibility parameter Extinction –Natural Conditions as Benchmark –CALPUFF

PROTOCOLS (CONTINUED) Cumulative Analyses of all new source growth Required under Some Conditions

LEVELS OF CONCERN Near Field –Screening |C|>=0.05 delta E >= 2 –Refined |C| >= 0.02 delta E >= 1 Distant/Multi-source –delta b ext >=10% –10%  delta b ext >=5% requires further analysis

ANALYSIS THRESHOLDS de minimis threshold for further analyses –0.4% change in extinction (single source) threshold for need for cumulative analyses –5% change in extinction (single source) –if a cumulative analyses has already been done

DECISION THRESHOLDS Near field –Screening |C|< 0.05 delta E < 2 –Refined |C|< 0.02 delta E < 1 Distant/Multi-source –single source (S.S) < 0.4% –cumulative delta b ext >= 10% but S.S. delta b ext < 0.4%

SPECIFIC CLASS I AREA INFORMATION Estimates of Natural Conditions –NAPAP East/West Estimates for Aerosol By species Non-hygroscopic components Hygroscopic components –Extinction calculation algorithm –Rayleigh extinction –Site specific or interpolated relative humidity adjustment factors