🌫️ AERMOD · AERMET · Odours · PM10 · PM2.5 · SOx · NOx · EIA · EPA · Ley 24.051

Air Pollutants & Dispersion Modelling

Atmospheric dispersion studies for EIA, permit compliance and odour management — using EPA AERMOD, the international regulatory standard model.

Biogroup applies AERMOD (the US EPA preferred regulatory model since 2005) to predict the atmospheric dispersion of industrial emissions from point, area and volume sources — modelling ground-level concentrations of criteria pollutants, toxic air contaminants and odorous compounds and comparing results against Argentine Ley 24.051 / Decree 831/93 Table 11 air quality standards and WHO guidelines.

With the help of mathematical dispersion models it is possible to calculate the reach of a toxic cloud from an industrial chimney — allowing determination of the probability of exposure and the severity of health impacts on the surrounding population before any incident occurs.

AERMOD / AERMET
EPA regulatory standard
Odour modelling
D/T · ou/m³ · exceedance
EIA support
Baseline · impact · mitigation
+35 years
Air quality expertise
🏭
EIA and permit compliance
Atmospheric dispersion studies for Environmental Impact Assessment (EIA) submissions and operating permit compliance — demonstrating that ground-level concentrations will not exceed Ley 24.051 Table 11 air quality guidelines at sensitive receptors.
👃
Odour impact assessment
Modelling of odorous compounds from animal facilities, agro-industrial plants, wastewater treatment and composting operations — predicting odour exceedance frequency at sensitive receptors for regulatory approval and community complaint response.
☠️
Toxic air contaminant studies
Determination of ground-level concentrations of toxic air contaminants (TACs) — assessing the cancer and non-cancer health risk to the surrounding population from chronic industrial air emissions.
AERMOD — the EPA regulatory dispersion model
AERMOD — AMS/EPA Regulatory Model Improvement Committee (AERMIC) Dispersion Model
The US EPA preferred regulatory model · EPA 40 CFR Part 51 · global standard since 2005

AERMOD is a steady-state Gaussian plume model that incorporates boundary layer theory, including the treatment of both surface and elevated sources, as well as simple and complex terrain. It is the US EPA preferred model for near-field applications (50 km or less) and the international regulatory standard for industrial source impact assessment studies.

📊 AERMOD — Dispersion model
Steady-state Gaussian plume · planetary boundary layer (PBL) parameterisation · surface and elevated source handling · simple and complex terrain · point, area, volume and line sources · fumigation · building downwash (PRIME)
🌡️ AERMET — Meteorological processor
Processes hourly surface and upper-air observations to derive PBL parameters (Monin-Obukhov length, mixing height, friction velocity, convective velocity scale) required by AERMOD · 1–10 years of local meteorological data
🗺️ AERMAP — Terrain processor
Digital elevation model (DEM) processing to characterise site terrain · source and receptor elevation extraction · complex terrain modelling with hill-height scale computation
AERMOD vs ISCST3: AERMOD replaced ISCST3 as the EPA preferred model in 2005. Biogroup uses AERMOD for all new studies — the only model accepted by Argentine environmental authorities (SAyDS, provincial agencies) for regulatory submissions.
Air pollutants — classification, physical state and health significance
The scientific framework — understanding what is being modelled
Air pollution is defined as the presence in the atmosphere of contaminants that alter its composition and affect any ecosystem component. Accurate dispersion modelling requires understanding the physical and chemical properties of each pollutant — because they determine the source term, transformation reactions and health impact thresholds used in the model.
🏭 Criteria pollutants (primary)
• SO₂ — Sulphur dioxide: combustion of sulphur-containing fuels · Ley 24.051 Table 8 annual and 24h standards
• NOₓ — Nitrogen oxides: high-temperature combustion · precursor to O₃ and fine particulate matter (PM2.5)
• CO — Carbon monoxide: incomplete combustion · 8h and 1h standards
• PM10 — Inhalable particles ≤10 µm · penetrate to bronchi and bronchioles
• PM2.5 — Fine particles ≤2.5 µm · reach alveoli · cross alveolar-capillary barrier into bloodstream · transport to remote organs
• Pb — Lead: smelters, battery recycling · quarterly standards
⚗️ Secondary pollutants & photochemistry
• Ozone (O₃) — formed from NOₓ + VOC + UV radiation · photochemical smog precursors · 8h ozone standard
• Sulphuric acid mist (H₂SO₄) — formed from SO₂ oxidation · acid deposition
• Nitric acid (HNO₃) — from NOₓ oxidation · acid rain component
• Secondary PM2.5 — formed from SO₂/NOₓ/VOC in-atmosphere reactions · sulphate and nitrate aerosols · regional transport
• PAHs on particles — benzo(a)pyrene as carcinogen marker
☠️ Toxic air contaminants (TACs)
• Benzene — human carcinogen (IARC 1) · petrol stations, refineries
• Formaldehyde — human carcinogen · combustion, resins
• 1,3-Butadiene — rubber manufacturing
• Acetaldehyde — combustion of ethanol fuels
• Dioxins/Furans (PCDD/PCDF) — incinerators, fires
• Heavy metals — Hg, As, Cd, Pb, Ni, Cr(VI) from industrial stacks
• HCl · HF — acid gas emissions from industrial processes
• H₂S — sewage, anaerobic processes · odour + toxicity
Particulate matter — the most critical regulated pollutant
Why particle size determines health impact — the respiratory deposition mechanism
Size governs where particles deposit in the respiratory tract — and therefore what health effect they cause. This is why PM10 and PM2.5 have separate regulatory standards.
>10 µm
Nose and upper airway
Filtered by nasal hairs. Deposited in nasal cavity. Minimal lung penetration.
2.5–10 µm (PM10)
Trachea, bronchi, bronchioles
"Respirable" fraction. Penetrates to conducting airways. Cleared by mucociliary escalator. Causes bronchitis and asthma exacerbation.
≤2.5 µm (PM2.5)
Terminal bronchioles and alveoli
"Fine particles". Reach the gas-exchange surface. Engulfed by alveolar macrophages. Cross alveolar-capillary barrier into the bloodstream. Transported to heart, brain and remote organs.
≤0.1 µm (UFP)
Alveoli → systemic circulation
Ultrafine particles. Maximum penetration. Highest surface area/mass ratio. Carry adsorbed PAHs, metals and organic compounds to remote organs.
Particles may contain organic compounds (polycyclic aromatic hydrocarbons, PAHs including benzo(a)pyrene) and inorganic compounds (heavy metals: Pb, As, Cd, Ni). These attached compounds enter the systemic circulation through the PM2.5 carrier mechanism — extending the health impact beyond the respiratory system.
Dispersion modelling services — what Biogroup models
🏭 Industrial point source modelling
AERMOD · stack emissions · ground-level concentrations · isoconcentration maps
Prediction of ground-level concentrations from industrial chimney emissions for all averaging periods — 1h, 8h, 24h and annual — at all receptors in the area of influence. Results compared against Ley 24.051 Table 11 and Table 8 air quality standards and WHO guidelines.
✓ Petroleum refining · power generation · cement and lime · metallurgy
✓ Chemical and petrochemical · fertilisers · incinerators
✓ Multiple source stacks — simultaneous impact assessment
✓ Building downwash with PRIME algorithm
✓ Seasonal and annual averaging periods
👃 Odour impact modelling
AERMOD · ou/m³ · D/T · exceedance frequency · annoyance thresholds
Odour modelling requires a specialised approach — because the critical metric is not the maximum concentration but the frequency at which the odour detection threshold is exceeded at a receptor. Biogroup models odour impact expressed in Odour Units (ou/m³) per EN 13725, calculating exceedance frequency as a percentage of hours per year.
✓ Agro-industrial plants · feedlots · composting · biogas facilities
✓ Wastewater treatment plants · landfills · rendering plants
✓ H₂S · NH₃ · mercaptans · reduced sulphur compounds
✓ Exceedance frequency at community receptors
✓ Buffer distance determination for permitting
☠️ Toxic plume modelling
TAC health risk · cancer risk · non-cancer HQ · chronic exposure
Chronic risk assessment from industrial air toxic emissions — modelling annual average ground-level concentrations and applying cancer potency factors (inhalation unit risk, IUR) and non-cancer reference concentrations (RfC) per EPA IRIS to calculate individual cancer risk and hazard quotients at all receptor locations.
✓ Hazardous air pollutants (HAPs) · NESHAP facilities
✓ Cancer risk mapping (ILCR 10⁻⁶ and 10⁻⁵ risk contours)
✓ Non-cancer HQ maps by organ system
✓ Cumulative multi-pathway risk assessment
🌳 Fugitive dust and area sources
Area source · volume source · open pit · unpaved road · construction
Modelling of PM10 and PM2.5 from diffuse sources that cannot be captured in a stack — unpaved roads, open storage piles, mining and quarrying operations, construction sites, grain handling. AERMOD area and volume source algorithms with AP-42 emission factor development.
✓ Construction dust impact assessment
✓ Open mine and quarry dust modelling
✓ Grain and fertiliser handling PM10/PM2.5
✓ AP-42 fugitive dust emission factor development
Atmospheric dispersion study workflow

A complete atmospheric dispersion study follows a systematic process from meteorological data acquisition through to the final impact assessment report with concentration maps.

1
Emission characterisation
Stack parameters (height, diameter, exit velocity, temperature, flow rate) and pollutant mass emission rates — from stack test data, process information or emission factor calculations (AP-42).
2
Meteorological data processing with AERMET
1–10 years of hourly surface and upper-air observations from the nearest representative station. AERMET derives boundary layer parameters (mixing height, Monin-Obukhov length, friction velocity) for each hour.
3
Terrain processing with AERMAP
Digital elevation model (DEM) processing to extract terrain elevations at all source and receptor locations. Critical for sites in complex terrain.
4
Receptor grid definition
Cartesian or polar grid of discrete receptors surrounding the facility, with higher density near the fence line and at sensitive receptor locations (schools, hospitals, residential areas).
5
AERMOD dispersion modelling
Multi-year simulation for all source-receptor combinations. Output: pollutant concentration at each receptor for all averaging periods (1h, 8h, 24h, annual).
6
Results analysis and report
Comparison against regulatory standards · isoconcentration maps · identification of maximum impact receptors · exceedance analysis · mitigation recommendations.
Air quality standards — Argentine and international benchmarks
Reference values applied in Biogroup dispersion study reports
🇦🇷 Argentine standards
• Ley 24.051 / Decree 831/93
• Table 8 — ambient air quality standards
• Table 11 — emission limits from point sources
• Resolution SMA Santa Fe
• Provincial: OPDS Buenos Aires · Córdoba regulations
🌍 WHO Guidelines (2021)
• PM2.5: 5 µg/m³ annual · 15 µg/m³ 24h
• PM10: 15 µg/m³ annual · 45 µg/m³ 24h
• NO₂: 10 µg/m³ annual · 25 µg/m³ 24h
• SO₂: 40 µg/m³ 24h
• O₃: 100 µg/m³ peak season daily 8h
🇺🇸 EPA NAAQS
• PM2.5: 9 µg/m³ annual · 35 µg/m³ 24h
• PM10: 150 µg/m³ 24h
• NO₂: 100 µg/m³ annual · 189 µg/m³ 1h
• SO₂: 75 ppb 1h · 0.5 ppm 3h secondary
• O₃: 70 ppb 8h · CO: 9 ppm 8h
Applications — when a dispersion study is required
📋
Environmental Impact Assessment
Atmospheric chapter of EIA for new industrial facilities — demonstrating compliance with air quality standards at the nearest sensitive receptors before construction approval.
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Operating permit renewal
Demonstration that current emissions are not causing exceedances of ambient air quality standards or causing significant impact beyond the facility boundary.
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Odour complaint response
Modelling to identify the emission source responsible for community odour complaints — and to demonstrate the impact of proposed mitigation measures.
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New source siting
Selection of optimal stack height, location and design parameters to minimise ground-level impact. Stack height optimisation studies.
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Environmental litigation
Defensible dispersion modelling results for expert witness use in disputes about industrial air quality impacts on neighbouring properties.
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IFC/World Bank projects
Atmospheric dispersion modelling to IFC EHS Guidelines performance standards for project finance transactions.
Official registrations
Provincial registry
Official Registry of Environmental Consultants, Experts and Expert Witnesses
Province of Santa Fe, Argentina
Ministerial registry
Registry of Environmental Impact Assessment Consultants
Ministry of Environment, Argentina
Related services
AERMOD · AERMET · Odours · PM10 · PM2.5 · EIA · EPA · Ley 24.051
Need an atmospheric dispersion study?
From a single-source EIA stack impact assessment to a multi-pollutant cumulative impact study with odour modelling — Biogroup provides AERMOD-based dispersion studies accepted by Argentine and international environmental authorities.
Request a dispersion study →
📞 +54 341 425-6431 📞 +54 341 447-4486 ✉ biogroup@biogroup.com.ar 📍 3 de febrero 920 · Rosario, Argentina Mon–Fri 08:00–17:00