A review of the impact of transient luminous events on the atmospheric chemistry: Past, present, and future

Atmospheric electricity has been intensively studied during the last 30 years after the discovery in 1989 of different forms of upper atmospheric electrical discharges (so-called Transient Luminous Events) triggered by lightning in the troposphere. In spite of the significant number of investigations that led to important new results unveiling how lightning produces a zoo of transient electrical discharges from the upper troposphere to the mesosphere, there is still no clear understanding about how all sort of TLEs - including those that occur inside thunderclouds - can contribute to the chemistry of the atmosphere both at the local and global scale. This review paper aims at presenting a perspective on the TLE atmospheric chemistry research done in the past, in the present as well as to describe some of the challenges that await ahead to find the true scientific importance of the non-equilibrium atmospheric chemistry triggered by TLEs. This review comes to conclude that while the global chemical impact of elves and halos are almost negligible, the large scale chemical impact of sprites, blue jets and blue starters and that of impulsive cloud corona discharges might be non-negligible in terms of their possibly measurable contribution to important greenhouse gases such as ozone and nitrous oxide (N<SUB>2</SUB>O). Being the third strongest greenhouse gas (after carbon dioxide and methane) and by having the ability to deplete ozone, precise determination of atmospheric N<SUB>2</SUB>O sources is of increasing and pressing demand. A new era in atmospheric electricity is just emerging in which dedicated scientific space missions (ISS-LIS, ASIM) together with geostationary lightning sensors (since 2016) and new micro-scale and parameterizations of TLEs in general atmospheric chemistry circulation models will hopefully help to start clarifying the full role of TLEs in the chemistry of the atmosphere.