Downwind Ground-Level Concentration Screen (Gaussian)

From the Gaussian plume equation with ground reflection. Inputs are entered in US units and converted once to the SI the published curves are drawn in. Two things dominate the answer and neither is the emission rate. The first is EFFECTIVE HEIGHT, which enters squared inside an exponential: halving it multiplies the ground-level concentration several times over, which is why plume rise matters as much as the stack itself, and effective height is stack height plus that rise. The second is STABILITY, which moves the answer by more than an order of magnitude between an unstable afternoon and a stable night. That is why this reports WHERE the maximum sits rather than only the concentration at the distance entered: the maximum is not at the fence line and not at the horizon, and its location moves with stability. A stable plume stays coherent and aloft, giving almost nothing close in and then reaching the ground farther out, so a receptor screened at one distance under one condition has not been screened. The bundled Pasquill-Gifford coefficients are the standard rural power-law fits; urban terrain disperses differently, and they approximate curves drawn from a limited experimental base. A flat-terrain, steady-state, single-source screen with no chemistry: it does not address terrain, building downwash, complex or elevated receptors, plume depletion, deposition, reaction, calm winds (where the model breaks down rather than merely losing accuracy), fumigation, multiple sources, or averaging-time conversion, so the result is a short-term centreline value and not an annual average. It is not a regulatory dispersion model and its result is not a compliance demonstration. The applicable modelling guideline, a regulatory model, and a qualified air quality professional govern.

the Gaussian plume equation with ground reflection on the plume centreline: C = Q / (pi u sigma_y sigma_z) x exp(-H^2 / (2 sigma_z^2)), with sigma_y and sigma_z from the standard Pasquill-Gifford rural power-law fits sigma = a x^b by stability class.

A flat-terrain, steady-state, single-source screening estimate with no chemistry. The bundled Pasquill-Gifford coefficients are the standard RURAL fits; urban terrain disperses differently, and they approximate curves drawn from a limited experimental base. It does not address terrain, building downwash, complex or elevated receptors, plume depletion, deposition, reaction, calm or low wind speeds, fumigation, multiple sources, or averaging-time conversion -- the result is a short-term centreline value, not an annual average. It is NOT a regulatory dispersion model and its result is not a compliance demonstration.

One closed-form equation and a published power-law coefficient set; no proprietary model is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: emission_rate_lb_hr, effective_height_ft, wind_mph, distance_mi, stability_class, alt_stability_class, sigma_y_m, sigma_z_m, exponential_term, concentration_ug_m3

• Rural Pasquill-Gifford coefficients urban terrain disperses differentlythe applicable modelling guideline
• Flat terrain, no downwash terrain and building effects can dominate a real sitea regulatory dispersion model
• Not a compliance demonstration a short-term centreline screen, not an annual averagethe air quality authority