Datensatz

Zusammenfassung

Through observations of reactive nitrogen species, volatile organic compounds and O3 in the Rambouillet
forest near Paris, France, (as part of the ACROSS campaign, 2022) we have gained insight into processes
controlling NOX, peroxy nitrates and alkyl nitrates in an anthropogenically impacted forest
environment. O3 mixing ratios displayed a strong diel profile at the site, which was driven by a variable
but generally rapid deposition to soil and foliar surfaces. Only when the O3 mixing ratio was sufficiently
low (and thus the NO lifetime sufficiently long), were sustained NO peaks observed above the
instrumental detection limit, enabling derivation of average NO emission rates from the soil of ~1.4 ppbv
h-1. Observations of the lack of increase in NO2 at night, despite a significant production rate from the
reaction of NO with O3, enabled an effective lifetime of NO2 of ⁓0.5-3 h to be derived. As the loss of NO2
was not compensated by the formation of gas- or particle-phase reactive nitrogen species it was
presumably driven by deposition to soil and foliar surfaces, or any products formed were themselves
short-lived with respect to deposition. Box modelling has been used to understand the sources of organic
nitrates in this study. The atmospheric effective lifetime of peroxy nitrates and alkyl nitrates in this
environment were determined to be of the order of 1-3 hours, which is approximately the same as for
NO2. We conclude that the nighttime deposition of reactive nitrogen plays a major role in limiting the loss
of nitrogen from the ecosystem and also in reducing the daytime (photochemical) formation of O3 at the
site