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Local Air Quality & Noise Module

LAQ impact assessment uses a specially developed model suitable for AIM, and industry standard noise codes are utilized to determine local noise contours. The module is designed to produce output both for the purposes of scientific inquiry and regulatory compliance predictions. As such, outputs are in terms of industry-standard metrics where possible.

The LAQ component of the module predicts dispersion of pollutants in the vicinity of airports, with particular focus on NOX, NO2, PM10, and PM2.5. The module can also predict the dispersion of other critical pollutants for which emissions databases are available, e.g. SOX, CO and UHC. It should be noted however that the emission levels of SOX, CO and UHC from aircraft engines are not currently thought to be of significant public health concern, and accordingly their dispersion is rarely of interest as compared to urban background levels.

The regulations for aircraft engine emissions are based on NOX without speciation into NO and NO2. Since NO2 is a hazardous pollutant, while NO is not, air quality regulations (as opposed to emissions regulations) are in terms of NO2. There is considerable interest in chemical reactions involving NO, NOX, O3, etc., and how best to incorporate these into operational models. Regulations exist for pollutants concentrations averaged annually and over several shorter time periods.

Observation from airport air quality monitoring stations allows determination of what particular pollutants and what averaging periods are critical. It has been found (e.g. the Project for the Sustainable Development of Heathrow, 2006) that short time averaged concentration regulations are not exceeded, while annual limits are of major concern at busy airports. The LAQ portion of the module is therefore primarily concerned with annual averages. Emissions data for the dispersion model are taken primarily from the Airport Activity Module, which itself receives aircraft class emissions data from the Aircraft Technology & Cost Module. As well as direct aircraft emissions, their support equipment is also of concern. Additional emissions data are required as an input to the module for major fixed installations (e.g. from heating plants), landside vehicular traffic within the airport perimeter, and from vehicular traffic outside the airport perimeter but accountable to airport activity. The goal is to determine the total air quality signature of the airport, as studies have shown that all of the aforementioned sources are significant.

The implementation of the LAQ portion of the module is distinct from existing local air quality impact assessment tools such as LASPORT, ADMS-Airport and EDMS, in that it is designed to perform calculations several orders of magnitude more quickly. This is necessary as it is intended for application to a large number of airports within AIM at an appropriate spatial and temporal resolution, and is achieved by using a lumped model with temporal averaging. The dominant variables that will determine the local pollutant concentrations have been observed to be background concentration, pollutant emissions within the airport perimeter, pollutant emissions outside the airport perimeter but attributable to the airport, and the meteorology of the local area in an appropriate statistical format. Other relevant variables are the spatial and temporal distribution of the emissions, as well as NO, NOX and O3 chemistry. Surface roughness has been found to be of less significance, and only key chemical reactions need to be considered. As far as ground level pollutant concentrations are concerned, contributions from airborne emissions below a threshold altitude are accounted for. This threshold altitude (conventional for LAQ studies) will be subject to further investigation but is currently set at 3000 ft.

The module will enable the assessment of aviation policy LAQ implications, particularly in the context of the European and US regulatory framework. Policies under study include part-time/dynamic mitigation strategies, for example encouraging particular operational procedures under certain wind conditions known to cause local air quality problems. In addition, LAQ metric contours are fed to the Regional Economic Impacts Module to assess their wider effects, for example by costing their impacts on health in local communities around airports.

The purpose of the noise component is to assess the noise impacts of the operations being modelled in the Airport Activity and Aircraft Movement Modules. Several industry-standard codes are available (e.g. the FAA’s Integrated Noise Model (INM) and Wyle Laboratories NMSim) and these are utilised in the module to assess the noise impacts of key variables, including different fleet mixes and routing structures. The codes can assess impacts against a variety of metrics, including various noise metrics (e.g. LAmax and DNL contour locations and areas) and population exposure. These are fed to the Regional Economics Module to assess impacts such as property valuation impacts or other societal costs of location within a given noise contour.