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Although the Montreal Protocol has been successful in reducing the emissions of long-lived ozone-depleting substances, certain unregulated, chlorinated very short-lived substances (VSLS, lifetimes < 6 months) are believed to be having an increasing impact on stratospheric ozone depletion. The major sources of the chlorinated VSLS are anthropogenic. Emissions of chlorinated VSLS have been reported to be increasing from both bottom-up estimates and observations in recent years, among which dichloromethane (DCM) is the most abundant. Emissions from East Asia have been identified as contributing significantly to this increase (Oram et al., 2017; Claxton et al., 2020; Adcock et al., 2021; An et al., 2021).Here we use synthesis inversion to derive an estimation of DCM emissions with a focus on East Asia, with input from the TOMCAT/SLIMCAT 3-D offline chemical transport model (CTM), a gridded annual global emission estimate, and aircraft observations from three recent campaigns - POSIDON (2016, https://csl.noaa.gov/projects/posidon/), StratoClim (2017, http://www.stratoclim.org/), and ACCLIP (2021, https://www2.acom.ucar.edu/acclip). The CTM contains the production and loss of DCM and is driven by reanalysed meteorology (Chipperfield, 2006), with gridded emission field of DCM (Claxton et al., 2020). In the model we set up more source regions than previous studies based on prior information, transport pathways into stratosphere, and the distribution of major city clusters. The inversion is performed by finding the minimum of the cost function (Tarantola and Valette, 1982): xa = xb+ [GTR-1G + B-1]-1GTR-1[y - Gxb], where y has the observations, xb is the prior estimate, B and R are the error covariance matrix of the prior estimates and the observations respectively, and G is the sensitivity matrix, as an operator mapping the emissions onto the observations by the CTM. Then xa can be calculated as known as the posterior estimate. Coupling the model and observations, xa is considered the best estimate and reduces the errors in the prior estimate.We will present our analysis of DCM emissions up to the present day and compare them with previously published values and longer-term trends.References:Adcock et al., 2021, JGR Atmos., https://doi.org/10.1029/2020JD033137.An et al., 2021, Nat. Commun., https://doi.org/10.1038/s41467-021-27592-y.Chipperfield, 2006, QJR Meteorol. Soc., https://doi.org/10.1256/qj.05.51.Claxton et al., 2020, JGR Atmos., https://doi.org/10.1029/2019JD031818.Oram et al., 2017, ACP, https://doi.org/10.5194/acp-17-11929-2017.Tarantola and Valette,1982, Rev. Geophys., https://doi.org/10.1029/RG020i002p00219.

Whole Air Samples (WAS) were collected as part of the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign in the Upper Troposphere-Lower Stratosphere (UTLS) region during Summer 2021 and 2022. Grid-Rad and satellite imagery were used to identify regions of overshooting convection, and areas with outflow from the overshooting were targeted by the DCOTSS aircraft using trajectory models and in-situ measurements. Because a wide range of trace gases with different atmospheric lifetimes and sources are measured, WAS can provide insight into the processes that influence trace gas composition of the UTLS over North America. We investigate the tropospheric tracer relationships within and around these deep convective regions to determine the extent of penetration of tropospheric gases into the lower stratosphere (LS). Compounds such as ethane and ethyne with short (< 6 months) tropospheric lifetimes do not reach the LS without rapid transport from deep convection, and we observe cases where these gases are elevated above stratospheric background, typically well correlated with other tropospheric tracers (e.g. CO). However, the relationship between enhanced water vapor from overshooting convection and tropospheric tracers is more complex. Further, we show that ratios between different trace gas species can help identify and distinguish air mass types (e.g., biomass burning, oil and gas production, urban influence, etc.). Finally, we determine the Cl- and Br- halogen budgets for 2021 and 2022 stratosphere over N. America and the contribution of very-short-lived organic halogen species.

One of the scientific objectives of the Asian Summer Monsoon Chemical & CLimate Impact Project (ACCLIP) project was to sample the chemical content of air processed in the Asian Summer Monsoon (ASM) to ascertain its role in UTLS ozone chemistry and re-distributing active species and short-lived climate forcers. Whole Air Samplers were used on the NSF/NCAR GV and NASA WB-57 aircraft to collect samples for analysis of a range of organic compounds, including organic halogens and hydrocarbons. From these samples we determined vertical distributions of individual species as well as correlations between species. We also determined total organic chlorine and bromine values and subdivided those into long-lived and short-lived contributions. In addition, we characterized the composition of samples that were collected within the ASM, within the ASM outflow, and within the background air. These results will be compared with model output from ACCLIP.

The upper troposphere and lower stratosphere (UTLS) region during the summer monsoon season over North America (NAM) is influenced by the transport of air from a variety of source regions over a wide range of timescales (hours to years). Age spectra are useful for characterizing the transport into such a region, and in this study we use and build on recently developed techniques to infer age spectra from trace gas measurements with photochemical lifetimes from days to centuries. We show that the measurements taken by the whole-air sampler instrument during the SEAC4RS campaign can be used to derive not only age spectra, but also path-integrated lifetimes of each of the trace gases and partitioning between North American and tropical surface source origins. The method used here can also clearly identify and adjust for measurement outliers that were influenced by polluted surface source regions. The results are generally consistent with expected transport features of the NAM but also provide a range of transport diagnostics (age spectra, trace gas lifetimes and surface source regions) that have not previously been computed solely from in situ measurements. These methods may be applied to many other existing in situ datasets, and the transport diagnostics can be compared with chemistry–climate model transport in the UTLS.