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Air Toxics & Modeling. Kentucky Division for Air Quality Taimur Shaikh Ph.D. Introduction. Air Toxics Implementation Ambient Sampling Modeling Risk Assessment Air Toxics Modeling Scope Sample Projects Various Toxics Modeled Facilities Pb NAAQS Modeled Facility.

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air toxics modeling

Air Toxics & Modeling

Kentucky Division for Air Quality

Taimur Shaikh Ph.D.


Air Toxics Implementation

    • Ambient Sampling
    • Modeling
    • Risk Assessment
  • Air Toxics Modeling
    • Scope
    • Sample Projects
      • Various Toxics Modeled Facilities
      • Pb NAAQS Modeled Facility
401 kar 63 020
401 KAR 63:020
  • Potentially hazardous matter or toxic substances regulation

“No owner or operator shall allow any affected

facility to emit potentially hazardous matter or

toxic substances in such quantities or duration as

to be harmful to the health and welfare of

humans, animals and plants.”

ambient sampling
Ambient Sampling


EPA Method TO-15

Analyze for volatile organics

Both grab and 24-hour composite samples


EPA Method TO-13A

Analyze for Poly-Aromatic Hydrocarbons

24-hour composites samples

  • Metals/Metalloids (Future)
    • PM10 including metals speciation
    • 24-hour (or greater) composite samples
air toxics modeling6
Air Toxics Modeling
  • Consists of multiple tiers
    • 1st tier – Screening via Screen3, conducted by permit reviewers
    • 2nd tier – AERMOD modeling using pertinent meteorological data and LULC data
    • 3rd tier – Same as 2nd tier but can require validated stack test emission rates, mass balances, and other data
  • Usually performed:
    • For new facilities/major modifications
    • In addition to sampled data
    • As a follow-up to citizen complaints
atra reference library
ATRA Reference Library

As part of the interpretation of 401 KAR 63:020, the Division

uses EPA’s Air Toxics Risk Assessment (ATRA) Reference

Library Volumes I, II, and III as the procedural direction for

conducting risk evaluations.

risk assessment
Risk Assessment
  • Air Toxics Reference Library (ATRA)
  • “Tiered” Risk Assessment
    • Three distinct tiers
      • The higher tiered assessments involve more complexity and have more rigorous data requirements
        • 1st tier – Risk is based on Screen3 output
        • 2nd tier – Risk is based on annual average from AERMOD (chronic assessment)
        • 3rd tier – Risk is based on ambient sampling data in addition to modeled values, at impacted individual, includes a more complex exposure and toxicity assessment
    • Based on EPA guidance documents
    • Most often, the data requirements limits the scope of the assessment
the tiered risk assessment
The Tiered Risk Assessment

Complete study-specific data, no assumptions - higher cost, lower uncertainty

Add quantitative uncertainty / variability analysis

More refined exposure assessment

More refined dispersion & exposure modeling

Simple dispersion model

Lookup Table


Tiers 2 & 3


Tier 1

No data, all assumptions - lower cost, high uncertainty

the tiered risk assessment10
The Tiered Risk Assessment

Tier 1

(Screening Level)

Tier 2

(Moderate Complexity)

  • Lookup tables
  • Exposure = maximum offsite levels
  • Simple dispersion modeling (MEI)
  • No data – all assumptions
  • Lower cost – high uncertainty
  • Conservative results – consistently over-estimates risk
  • Exposure = exposure assessment
  • Detailed site-specific modeling (MIR)
  • Complete study-specific data
  • No assumptions
  • Higher cost – lower uncertainty
  • Exposure = residential air levels
  • More refined dispersion & exposure modeling (MIR)
  • Moderate cost

Tier 3

(High Complexity)

air toxics domain
Air Toxics Domain
  • All higher-level (tiers 2 & 3) risk assessments
  • As directed by DAQ Management, risk assessments involving:
      • Unlisted pollutants
      • Acute health effects
      • Bioaccumulation
      • Cumulative risk
        • Carcinogenic risk
        • Target organ specific hazard index
      • Emissions from multiple sources
      • Environmental damage
sample projects
Sample Projects
  • Examples of incorporating modeling into Air Toxics:
    • Toxics analysis – Dioxins & Furans
    • Toxics analysis – Hydrazine
    • Toxics analysis – HF modeling under

401 KAR 53:010

  • Modeling that belongs to Air Toxics by managerial default:
    • NSR/PSD review
    • Site evaluation of monitors for the Pb NAAQS.
toxics analysis dioxins furans
Toxics Analysis – Dioxins & Furans
  • Secondary Aluminum Smelter
    • Emissions of Dioxin and Furans covered under Subpart RRR – NESHAP for Secondary Aluminum Production
    • Facility could not demonstrate capture efficiency due to deviations from RRR
    • Modeled annual average (4.3*10-7 g/m3) exceeds 1*10-6 carcinogenic risk (6.4*10-8 g/m3)
    • The facility is operational at the moment but has taken a production limit
toxics analysis hydrazine
Toxics Analysis – Hydrazine
  • A specialty chemical facility manufacturing organic and organometallic compounds
    • The facility was permitted to emit Ni, Cd, Pb, and hydrazine
    • After initial modeling with AERMOD, modeled ambient concentrations exceeded 1:1,000,000 carcinogenic risk with cadmium driving the risk at 1:1,000
  • After our investigation, the facility choose to remove Cd, and Ni and reduce Pb and hydrazine emissions
toxics analysis hf
Toxics Analysis - HF
  • 401 KAR 53:010 is the Kentucky Ambient Air Quality Standards which include standards for HF
  • These are not to be exceeded more than once per year
  • A ceramic and tile manufacturing facility was modeled to show compliance
pb naaqs
  • The modeling was used in site selection criteria for a Pb monitor in conjunction with the new Pb National Ambient Air Quality Standard (10/15/2008)
pb from a coal fired power plant
Pb From a Coal Fired Power Plant
  • Used air dispersion modeling of a coal fired power plant to site a monitor for the Pb NAAQS
  • The NAAQS is based on a 3-month rolling and quarterly average
  • Compared the one month and annual averages to choose the site for the monitor
  • Air dispersion modeling:
    • Features prominently in the KY Air Toxics strategy
    • Is applied in situations where monitoring is not feasible due to cost or time involved
    • Can be binding from a regulatory standpoint
    • Yields useful information for risk assessment

Dr. Taimur Shaikh -

Kentucky Division for Air Quality – (502)564-3999 ext. 4480