Aviation contributes to local and remote air pollution by emitting ultrafine particles and gaseous pollutants. In addition to fresh exhaust emissions, secondary particle formation takes place in the atmosphere via reactions involving photolysis and atmospheric radicals. However, the compositions of long-transported, atmospherically aged exhaust emissions from aviation remain poorly described. Secondary emissions may cause major health effects while also potentially influencing the radiative forcing in the atmosphere. Here, our aim is to examine the impacts of photochemical aging on the jet engine exhaust emissions using kerosine-based jet fuel JP-8. Laboratory experiments were performed with a test rig containing a combustion chamber of an original small jet engine. A stable operation condition was determined so that the fresh emissions were comparable to those of an average land- and takeoff cycle of a commercial aircraft. Photochemical aging was conducted using the Photochemical Emission Aging flow Reactor (PEAR; Ihalainen et al 2019), with hydroxyl radical (OH) exposure equivalent to 2 days of aging in the atmosphere. Further tests at different exposures (equivalent to 0.5 – 7 days of OH exposure) were also performed. Online methods included, for example, aerosol mass spectrometer and proton-transfer-reaction time-of-flight mass spectrometer for chemical composition analysis, scanning mobility particle sizer (SMPS) for the particle size and number determination, 7-λ aethalometer for online assessment of the particle light absorption, and aerodynamic aerosol classifier coupled with an SMPS for particle density assessment. Further, offline analyses of gas phase carbonyls and thermal-optical carbon analyses of filter samples were performed. The light absorbance by the water-soluble organic carbon (WSOC) was determined by ultraviolet-visible (UV-Vis) absorption spectrophotometry. Fresh particle emissions were minor, and had bimodal particle size distributions composed of sub-50nm particles (Fig. 1). Scanning electron microscopy imaging confirmed that there was no soot in the exhaust emissions. Photochemical aging led to notable particle growth by substantial secondary organic aerosol formation, which increased the particle mass by a factor of 300. Aging consumed the gas-phase aromatic and polycyclic hydrocarbons while forming small carbonylic compounds. Aging caused a significant increase in the light absorption at lower visible wavelengths (Fig. 1). Based on the aethalometer results, absorption was further enhanced when the photochemical exposure was extended. The imaginary refractive indices (k) of secondary WSOC were 0.0066 and 0.00059 at 365nm and 550nm, respectively. The results show that substantial amounts of weakly absorbing organic brown carbon may be formed in the atmosphere from jet engine exhausts. This work was supported by Horizon2020 project ULTRHAS (agreement 955390) and Research Council of Finland (grant 341597).    «

Aviation contributes to local and remote air pollution by emitting ultrafine particles and gaseous pollutants. In addition to fresh exhaust emissions, secondary particle formation takes place in the atmosphere via reactions involving photolysis and atmospheric radicals. However, the compositions of long-transported, atmospherically aged exhaust emissions from aviation remain poorly described. Secondary emissions may cause major health effects while also potentially influencing the radiative forc...    »