According to a study by Arpa Veneto (http://www.arpa.veneto.it/arpav/chi-e-arpav/file-e-allegati/dap-venezia/aria/Relazione_tecnica_emissioni_aeroportuali.pdf),
airports are responsible for the emission of pollutants produced by combustion activities: ozone (which is not directly emitted but generated by precursors' emissions), carbon monoxide, nitrogen oxides, volatile organic compounds and particulate matter.
Nevertheless, airports contribution to total pollution is relatively marginal. Indeed, in the Atmospheric Emission Inventory Guidebook by EEA (European Environment Agency), in the chapter dedicated to air transport there are some useful comments about airport-generated emissions. As an example, CO2 emissions by airports are about 2% of the total man-made emissions.
The following table is taken from the European Environment Agency report on aviation dated July 2017; it outlines the contribution of the emissions produced by air traffic to the total, per several pollutants.
Generally, in the different phases of a flight, aircrafts produce different pollutants.
Aircraft engines mainly emit nitrogen oxides (NOX), carbon monoxide (CO), volatile organic compounds (VOC), sulphur dioxide (SO2) and particulate matter (PM), apart from carbon dioxide (CO2) and water (H2O) in the form of steam. Nitrogen oxide and particulate matter emissions are mainly produced during take-off and climbing phases, while carbon monoxide and hydrocarbons are mainly emitted during taxiing.
Moreover, releases to land are linked to airport activities: generating sets, auxiliary power units, ramp vehicles, engine tests, utility vehicles, energy production plants, work equipments and maintenance equipments.
The road traffic (personal vehicles, hired vehicles, taxis, buses, shuttle buses…) produced to serve the airport and its users should be added to all these sources.
The entire aeronautical industry is constantly and formally committed in emissions abatement, most of all in the reduction of climate-changing emissions (CO2), by mainly following two specific programs as per ICAO Resolution A39-3. These two programs are addressed, respectively, to airlines and aircraft manufacturers (CORSIA – Carbon Offsetting and Reduction Scheme for International Aviation) and to airports (ACA – Airport carbon Accreditation).