Aircraft observations above London city during a day and a night: ozone and alkyl nitrate formation

Measurements of NO2, ΣPNs, ΣANs and HNO3 have been done using a TD-LIF instrument, developed at the Physics and Chemistry department of L’Università degli Studi dell’Aquila and installed on aboard the FAAM BAe-146 research aircraft, during the RONOCO (ROle of Nighttime chemistry in controlling the Oxidising Capacity) campaign. We analyse in detail the chemical mechanisms that have been established during two flights (B536 and B548) characterized by a similar track (flying above the M25 highway around London) and carried out during a day (B548) and a night (B536). During In the daytime flight, the chemical species around London present a net spatial distribution defining two distinct areas: the East London region (up-wind) with an older and less polluted (lowest concentrations of NOx) air masses and the West London region (down-wind) with fresh emissions and more polluted (highest concentrations of NOx with peaks of about 30 ppb). In correspondence of these peaks strong ozone tritation phenomena due to the high NOx levels are verified with a corresponding increase of the ΣANs concentrations. In order to verify the impact of the high concentrations of alkyl nitrate (with maximum values of about 3 ppb) on the tropospheric ozone budget, the production and loss of ozone and ΣANs has been studied using the approaches suggested by Cazorla et al. (2012) and Rosen et al. (2004). The slopes between the production of ozone and alkyl nitrates confirm that around London the ΣANs formation on one side and the relative ozone loss on the other side represent significant processes. Moreover, the loss of the O3 during the nocturnal flight (B536) is less evident that during the B548 flight.