This is a repository copy of Acceleration of global N2O emissions seen from two decades of atmospheric inversion.

Chloroform (CHCl3) contributes to the depletion of the stratospheric ozone layer. However, due to its short lifetime and predominantly natural sources, it is not included in the Montreal Protocol that regulates the production and uses of ozone depleting substances. Atmospheric chloroform mole fractions were relatively stable or slowly decreased during 1990-2010. Here, we show that global chloroform mole fractions increased after 2010, based on in situ chloroform measurements at seven stations around the world. We estimate that the global chloroform emissions grew at the rate of 3.5% yr-1 between 2010 and 2015 based on atmospheric model simulations. We use two regional inverse modelling approaches, combined with observations from East Asia, to show that emissions from eastern China grew by 49 (41-59) Gg between 2010 and 2015, a change that could explain the entire increase in global emissions. We suggest that if chloroform emissions continuously grow at the current rate, the recovery of the stratospheric ozone layer above Antarctica could be delayed by several years. 22. Hossaini, R., et al. A multi-model intercomparison of halogenated very short-lived substances (TransCom-VSLS): linking oceanic emissions and tropospheric transport for a reconciled estimate of the stratospheric source gas injection of bromine. Atmos. Chem. Phys. 16, 9163-9187 (2016). 23. Yu, P., et al. Efficient transport of tropospheric aerosol into the stratosphere via the Asian summer monsoon anticyclone.

A B S T R A C T This paper describes the NO y plumes originating from lightning emissions based on 4 yr (2001Á2005) of MOZAIC measurements in the upper troposphere of the northern mid-latitudes, together with ground-and space-based observations of lightning flashes and clouds. This analysis is primarily for the North Atlantic region where the MOZAIC flights are the most frequent and for which the measurements are well representative in space and time. The study investigates the influence of lightning NO x (LNO x ) emissions on large-scale (300Á2000 km) plumes (LSPs) of NO y . One hundred and twenty seven LSPs (6% of the total MOZAIC NO y dataset) have been attributed to LNO x emissions. Most of these LSPs were recorded over North America and the Atlantic mainly in spring and summer during the maximum lightning activity occurrence. The majority of the LSPs (74%) is related to warm conveyor belts and extra-tropical cyclones originating from North America and entering the intercontinental transport pathway between North America and Europe, leading to a negative (positive) west to east NO y (O 3 ) zonal gradient with (0.4 ('18) ppbv difference during spring and (0.6 ('14) ppbv difference in summer. The NO y zonal gradient can correspond to the mixing of the plume with the background air. On the other hand, the O 3 gradient is associated with both mixing of background air and with photochemical production during transport. Such transatlantic LSPs may have a potential impact on the European pollution. The remaining sampled LSPs are related to mesoscale convection over Western Europe and the Mediterranean Sea (18%) and to tropical convection (8%).

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Abstract. For the first time, a plume-in-grid approach is implemented in a chemical transport model (CTM) to parameterize the effects of the nonlinear reactions occurring within high concentrated NO x plumes from lightning NO x emissions (LNO x ) in the upper troposphere. It is characterized by a set of parameters including the plume lifetime, the effective reaction rate constant related to NO x -O 3 chemical interactions, and the fractions of NO x conversion into HNO 3 within the plume. Parameter estimates were made using the Dynamical Simple Model of Atmospheric Chemical Complexity (DSMACC) box model, simple plume dispersion simulations, and the 3-D Meso-NH (non-hydrostatic mesoscale atmospheric model). In order to assess the impact of the LNO x plume approach on the NO x and O 3 distributions on a large scale, simulations for the year 2006 were performed using the GEOS-Chem global model with a horizontal resolution of 2 • × 2.5 • . The implementation of the LNO x parameterization implies an NO x and O 3 decrease on a large scale over the region characterized by a strong lightning activity (up to 25 and 8 %, respectively, over central Africa in July) and a relative increase downwind of LNO x emissions (up to 18 and 2 % for NO x and O 3 , respectively, in July). The calculated variability in NO x and O 3 mixing ratios around the mean value according to the known uncertainties in the parameter estimates is at a maximum over continental tropical regions with NO [−1.18, +1.93] ppb, in July, mainly depending on the determination of the diffusion properties of the atmosphere and the initial NO mixing ratio injected by lightning. This approach allows us (i) to reproduce a more realistic lightning NO x chemistry leading to better NO x and O 3 distributions on the large scale and (ii) to focus on other improvements to reduce remaining uncertainties from processes related to NO x chemistry in CTM.