Air Quality

Our air quality services include:

General Conformity Analyses

The Clean Air Act (CAA) requires that emissions from airport construction projects, for airports located in an area of poor air quality (designated as either “maintenance” or “nonattainment” for a particular criteria air pollutant), are reflected in the state’s air quality improvement plan (or state implementation plan—SIP).  Airport sponsors located in maintenance and nonattainment areas must follow General Conformity regulations (a section of the CAA) to receive FAA approval for expansion projects or capital funding.  If the project’s emissions are not properly accounted for in the SIP emission budget, federal law can delay or even prohibit project implementation.  In essence, this requires that an airport project whose emissions exceed a threshold (de minimis) be compared to the emission budget in the SIP.  Otherwise, an airport operator must completely offset air emissions resulting from a project.  Projects may not be undertaken until one of these conditions is satisfied.  

As required by 40 CFR 93.159(d), an airport sponsor is generally required to provide emissions inventories for each nonattainment pollutant for the following years:

• Baseline Year, as established in the SIP
• SIP-Specified Year, as established in the SIP
• Year of Maximum Emissions, generally the peak year of construction activities
• Furthest Reasonably Foreseeable Year, based on the time frames of development plans

The overall objective of our work is to ensure that all foreseeable airport development projects are included in the SIP so when FAA makes a future environmental determination, conformity can be demonstrated via the requirements of 40 CFR 93.158 (a) (1).  Given the numerous air quality regulatory agency personnel that will likely be involved in accommodating airport-related emissions in the SIP, considerable agency coordination will be required.  Our initial meetings with the state environmental regulatory agency usually focus on the regional and economic importance of future development projects and the sponsor’s desire to ensure an accurate and robust documentation of current and future emissions.  This consensus building approach is important because SIPs are amended infrequently and the sponsor’s request for inclusion in the SIP will be placing a work burden on the regulatory agency. 

Airport Emissions Inventories

The first step in any airport emissions inventory is to develop an inventory protocol which ensures a highly efficient and accurate accounting of on-airport emissions.  Our sophisticated understanding of the algorithms and the sources of default assumptions within the AEDT 2b air quality model allow us to model critical airport emissions sources accurately and efficiently.  Thus, rather than exclusively relying on air quality model defaults for emission sources, which can oftentimes be inappropriate, we will use actual operational data whenever possible.  This approach involves (1) interviewing sponsor staff, (2) consulting sponsor staff and air traffic control records, (3) utilizing commercial databases, and (4) conducting airport site visits and performing real-time measurements.  Not all emission sources can be measured directly. However, many emission sources, which account for a significant portion of on-airport emissions, can be quantified by visual and time measurements.  This includes aircraft APUs usage at the gate, ground support equipment (GSE) activity, and vehicular traffic.  When practical, a large and diverse volume of observed operational data are collected and then averaged, with data being weighted according to a number of different variables, such as time of day, equipment owner/operator, and weather conditions. 

It is vitally important that we closely coordinate the development of our emissions inventory protocol with the sponsor, regulatory agencies, and the FAA to ensure that our approach to data collection, operational assumptions, and air quality modeling methodologies are valid, reasonable, and consistent. Additionally, as data is being collected, we coordinate with all stakeholders to (1) ensure its accuracy and (2) seek their concurrence prior to performing the air quality modeling.