Air Quality

Example Projects


Drawing upon a team of experts with diverse backgrounds and areas of expertise, Gradient offers a wide range of air quality services, such as air monitoring data analysis and interpretation, design of air sampling plans, air dispersion modeling using regulatory models such as AERMOD and CALPUFF, meteorological data analysis, accidental chemical release modeling, occupational air emission evaluations, vapor intrusion and indoor air quality assessment, as well as indoor air exposure assessment, including indoor air modeling and design of indoor exposure simulation studies.

Gradient's air quality experts work hand-in-hand with our risk assessors to provide estimates of indoor and outdoor air pollutant exposures that are used as inputs for site-specific risk assessments. Our air quality experts also routinely conduct exposure assessments for indoor and outdoor air pollutants to support toxic tort litigation cases and are frequently called upon to provide expert witness testimony on air quality issues.

  • Source emission characterization
  • Gaussian dispersion modeling
  • Photochemical modeling
  • Visibility degradation and analysis
  • Accidental releases
  • Vapor intrusion
  • Air permitting
  • Remediation impacts

Cloudy sky

Example Projects

Air Quality Impacts and Potential Health Risks of Power Plant Soot

Full Description

Gradient assessed potential air quality impacts and health risks associated with particulate matter and trace metal constituents, including thallium and arsenic, emitted during upset events and normal operating conditions at a large coal-fired power plant. We reconstructed emissions and performed air dispersion modeling for short-term soot events, identifying maximum impact areas. We conducted toxicological assessments for potential worst-case exposures from the soot events.

Hydrogen Sulfide Exposure Near a Midwestern Concentrated Animal Feeding Operation

Full Description

Gradient evaluated the release of hydrogen sulfide (H2S) from barns and a waste lagoon at a large Midwestern hog farm. We conducted air monitoring to develop H2S emissions factors for several barns, a waste lagoon, and land application of liquid manure. We then modeled H2S concentrations downwind of the farm and compared the modeled values with published health benchmarks.

Air Modeling of Power Plant Sulfur Dioxide Impacts in a Nonattainment Area

Full Description

Gradient used both AERMOD and CALPUFF to predict maximum one-hour sulfur dioxide (SO2) concentrations at the SO2 nonattainment monitor for two coal-fired power plants, one located in the nonattainment area and one located outside the nonattainment area. We compared findings for the two power plants, as well as for the two different models, and examined the correlation between specific hour-to-hour modeled vs. measured SO2 concentrations.

Assessment of PM2.5 Air Quality and Potential Health Risks Posed by Urban Building Construction

Full Description

Gradient helped design a particulate matter (PM) air monitoring network and evaluated air quality data collected in the vicinity of a large construction project at a major university. We assessed potential health risks to children at a nearby daycare center from both long- and short-term PM2.5 exposures associated with construction-related activities and communicated these results to faculty, parents, and daycare center staff.

Indoor Air Exposures from a Commercial Printer

Full Description

To assess potential exposures and health risks associated with operation of a commercial printer and its soybean oil-based ink, Gradient developed testing protocols and oversaw implementation of an indoor air exposure study that included measurements for a comprehensive set of test analytes (mineral oil, carbon black, glycerol, aldehydes, VOCs, and SVOCs). Gradient conducted a toxicological assessment for analytes found in the study and evaluated the likelihood for potential health risks associated with air emissions from the printer.

Assessment of Ozone Exposure and Health Risks with US EPA's APEX and BenMAP Models

Full Description

Gradient developed ozone exposure and risk assessments using the US EPA's Air Pollutants Exposure (APEX) and Environmental Benefits Mapping and Analysis Program (BenMAP) models. Using APEX, we conducted a series of sensitivity analyses to assess how alternative model inputs impact exposure and risk assessment results. For BenMAP, we evaluated the impacts of using alternative model inputs, including air quality inputs and health effects functions, on ozone mortality estimates.

Remediation Monitoring Evaluation

Full Description

Gradient developed an air monitoring plan to be used during a manufactured gas plant site remediation to determine the adequacy of health-based action levels for benzene, toluene, and xylene. We used air modeling to develop air monitoring levels from toxicological data and evaluated air monitoring results to ensure that they were health protective.