Open-ALAQS provides a means to perform a four-dimensional inventory of emissions in which both the emissions from airport sources, such as aircraft operation activities, and the emissions from aircraft and non-airport sources, such as those from car traffic to/from the airport, are calculated, aggregated and subsequently displayed for analysis.
Once the inventory of emissions has been established, pollutant concentrations at the airport and in its surrounding area can be calculated over a given period of time using dispersion modelling (provided by AUSTAL2000 – see below). The system is compatible with European legislative requirements for 8-hour, 24-hour, and annual mean values of pollutant concentrations.
Open-ALAQS is developed as a plugin to an open-source geographic information system (QGIS), which simplifies the definition of the various airport elements (runways, taxiways, buildings, etc.) and allows the spatial distribution of emission concentrations to be visualised. It also uses an open-source database (SQLite), and is fully based on an open architecture, rendering it easily adaptable to other GISes and databases if necessary.
Open-ALAQS is also linked with another open-source application, AUSTAL2000, and together Open-ALAQS/AUSTAL2000 can be seen as a complete open-source airport local air quality tool suite (inventory of emissions, dispersion calculation, and concentration).
Open-ALAQS retains the philosophy and fully implements the functionalities of the original model.
Emissions from aircraft engines are calculated according to the fuel flow and emission indices of the ICAO Aircraft Engine Emissions Databank (AEED) for turbofan and turbojet engines, combined with the FOCA databank for pistons (and potentially FOI for turboprops). CO, HC and NOX emissions are calculated based on the Boeing Fuel Flow Method 2, which was implemented following the recommendations of the ICAO Doc 9889 Airport Air Quality Manual. The emissions of both volatile and non-volatile particulate matter (PM) are based on emission indices derived from the smoke number of the ICAO AEED following the First Order Approximation v3.0 (FOA3).
The correction of NOX emission indices for ambient conditions has also been implemented following the recommendations of the International Coordinating Council of Aircraft Industry Associations (ICCAIA). The ICAO AEED does not have emission certification standards for SOX. Emissions of SOX have been implemented according to the U.S. EPA recommendation for commercial aviation jet fuel. In the latest version of Open-ALAQS, the time-in-mode for each movement (arrival / departure) was derived from fixed-point profiles derived from the Aircraft Noise and Performance Database (ANP2.1). The switch between take-off and climb-out modes is performed on the first point of the profile strictly above 304.8 m. This method is referenced as «by mode» in Open-ALAQS. In the absence of operational fuel flows or profiles, the following percentages are used to approximate the fuel flow between the ICAO certification points reported in the ICAO aircraft engine databanks: 90% for take-off, 75% for climb-out, and 25% for approach.