Pasquill_gifford_briggs

Classic Gaussian plume dispersion model parameterized with Pasquill-Gifford-Briggs (PGB) stability classification and dispersion coefficients. Given the current puff position (lon, lat) and height above ground (z_agl), classifies atmospheric stability from near-surface meteorology (wind speed, solar radiation, cloud fraction, temperature lapse), selects Briggs dispersion-curve coefficients, computes the haversine downwind distance from the source, and evaluates horizontal (sigma_h) and vertical (sigma_z) dispersion widths and the ground-level Gaussian concentration (C_gl). Migrated from EnvironmentalTransport.jl@a48559c4 src/GaussianDispersion.jl:83. When coupled with Puff, lon/lat/z_agl are supplied by the Puff component; in standalone mode they are treated as constant parameters.