Oliver Kirner

Impact of acetone (photo)oxidation on HOx production in the UT/LMS based on CARIBIC passenger aircraft observations and EMAC simulations

Until a decade ago, acetone was assumed to be a dominant HOx source in the dry extra-tropical upper troposphere (ex-UT). New photodissociation quantum yields of acetone and the lack of representative data from the ex-UT challenged that assumption. Regular mass spectrometric observations onboard the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) passenger aircraft deliver the first representative distribution of acetone in the UT/LMS (UT/lowermost stratosphere). Based on diverse CARIBIC trace gas data and non-observed parameters taken from the model ECHAM5/MESSy for Atmospheric Chemistry, we quantify the HOx source in the UT/LMS from (photo)oxidation of acetone. The findings are contrasted to HOx production from ozone photolysis, overall the dominant tropospheric HOx source. It is shown that HOx production from acetone (photo)oxidation reaches up to 95% of the HOx source from ozone photolysis in autumn in the UT and on average ~61% in summer. That is, acetone is a significant source of HOx in the UT/LMS.

Comparing data obtained from ground-based measurements of the total contents of O3, HNO3,HCl, and NO2 and from their numerical simulation

Chemistry climate models of the gas composition of the atmosphere make it possible to simulate both space and time variations in atmospheric trace-gas components (TGCs) and predict their changes. Both verification and improvement of such models on the basis of a comparison with experimental data are of great importance. Data obtained from the 2009–2012 ground-based spectrometric measurements of the total contents (TCs) of a number of TGCs (ozone, HNO3, HCl, and NO2) in the atmosphere over the St. Petersburg region (Petergof station, St. Petersburg State University) have been compared to analogous EMAC model data. Both daily and monthly means of their TCs for this period have been analyzed in detail. The seasonal dependences of the TCs of the gases under study are shown to be adequately reproduced by the EMAC model. At the same time, a number of disagreements (including systematic ones) have been revealed between model and measurement data. Thus, for example, the EMAC model underestimates the TCs of NO2, HCl, and HNO3, when compared to measurement data, on average, by 14, 22, and 35%, respectively. However, the TC of ozone is overestimated by the EMAC model (on average, by 12%) when compared to measurement data. In order to reveal the reasons for such disagreements between simulated and measured data on the TCs of TGCs, it is necessary to continue studies on comparisons of the contents of TGCs in different atmospheric layers.

The representation of solar cycle signals in stratospheric ozone. Part II: Analysis of global models

Monthly and zonal mean coefficients for the 11 year solar cycle effect on stratospheric ozone derived from the CMIP6 ozone dataset. The coefficients are provided on a 3-D (latitude-pressure-month) grid and are derived using multiple linear regression of ozone against either: (1) the F10.7cm solar radio flux (cmip6_solar-o3_coeffs_per_SFU.nc); and (2) the 200-320 nm integrated spectral solar irradiance (cmip6_solar-o3_coeffs_per_Wm-2.nc) for the period 1960-2011. The coefficients are provided in terms of both % and mol mol-1 of ozone change. Also included are p-values for the ozone coefficients as a function of latitude-pressure-month. The dataset is provided in NetCDF format.

Chlorine nitrate in the atmosphere over St. Petersburg

Ground-based measurements of the total chlorine nitrate (ClONO2) in the atmosphere have been taken for the first time in Russia using the Bruker IFS-125HR infrared (IR) Fourier spectrometer (FS). The average error of the total ClONO2 measurements, performed in 2009–2012 in Peterhof, is (25 ± 10)%. The results have been compared with measurements performed using similar devices at the NDACC network, Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite measurements, and the total ClONO2 numerical simulation (performed using the EMAC chemical climatic model). The total ClONO2 seasonal variations are similar for three considered observation stations (Peterhof, Kiruna, and Eureka) with the maximum in February-March, which is more pronounced at higher latitudes. High correlations (R = 0.7–0.9) between the MIPAS satellite data, ground-based measurements near St. Petersburg, and the values calculated using the EMAC model have been revealed. The modeling data are on average smaller than the data of the ground-based and satellite measurements. An analysis of the seasonal variations in the total ClONO2 monthly average values in the St. Petersburg region indicated that this difference is caused by the fact that the model underestimated the maximal total ClONO2 values in the atmosphere.

Annual cycle and long-term trend of the methane total column in the atmosphere over the St. Petersburg region

The annual cycle and long-term trend of the methane total column in the atmosphere over the Petergof station (St. Petersburg State University) are analyzed on the basis of data obtained from Fourier-transform infrared spectrometry and EMAC-model calculations. The amplitude of the annual cycle of the total column of CH4 amounts to 2.1 and 1.5% according to experimental and model data, respectively. For the atmospheric column-averaged mole fraction of CH4, the amplitude of its annual cycle is smaller than that for its total column and amounts to 1.1 and 0.6% according to experimental and model data, respectively. The results of local continuous measurements of surface CH4 concentrations showed that, in 2013, the atmospheric column-averaged mole fractions of CH4 and the amplitudes of diurnal variations in its local concentration were characterized by the same dynamics of seasonal variations. An analysis made on the basis of simulation results showed that atmospheric conditions (under which Fourier-transform IR measurements were performed) could increase the amplitude of the annual cycle of the total column of CH4 2.5 times when compared to the true one. The results of Fourier-transform IR measurements and EMAC-model calculations showed that, during 2009–2012, the atmospheric concentration of CH4 increased at a rate of ~0.2% per year. If measurement data obtained in 2013 are added, this rate decreases to ~0.13% per year.

Validation of Atmospheric Numerical Models Based on Satellite Measurements of Ozone Columns

The time series of ozone columns measured with the SBUV satellite instrument over three subarctic stations (Saint Petersburg, Harestua, and Kiruna) are analyzed. The daily and monthly mean ozone values in the layers of 0–25, 25–60, and 0–60 km are compared with the results of simulations with RSHU and EMAC numerical models for the period of 2000–2015. Model data are in good agreement with satellite data both in general and in the cases of rapid short-term ozone loss. However, there are some differences between the models and measurements as well as between the two considered models. These differences require the more detailed analysis in order to modify model parameters. Experimental data demonstrate the increase in ozone columns in the layer of 25–60 km which amounts to 2.1 ± 0.7, 2.4 ± 0.7, and 1.5 ± 0.8% per decade for Saint Petersburg, Harestua, and Kiruna stations, respectively. The results of numerical simulations do not contradict these estimates.

Ozone Temporal Variability in the Subarctic Region: Comparison of Satellite Measurements with Numerical Simulations

Fourier and wavelet spectra of time series for the ozone column abundance in the atmospheric 0–25 and 25–60 km layers are analyzed from SBUV satellite observations and from numerical simulations based on the RSHU and EMAC models. The analysis uses datasets for three subarctic locations (St. Petersburg, Harestua, and Kiruna) for 2000–2014. The Fourier and wavelet spectra show periodicities in the range from ~10 days to ~10 years and from ~1 day to ~2 years, respectively. The comparison of the spectra shows overall agreement between the observational and modeled datasets. However, the analysis has revealed differences both between the measurements and the models and between the models themselves. The differences primarily concern the Rossby wave period region and the 11-year and semiannual periodicities. Possible reasons are given for the differences between the models and the measurements.

Revisiting the Mystery of Recent Stratospheric Temperature Trends

Simulated stratospheric temperatures over the period 1979-2016 in models from the Chemistry-Climate Model Initiative (CCMI) are compared with recently updated and extended satellite observations. The multi-model mean global temperature trends over 1979- 2005 are -0.88 ± 0.23, -0.70 ± 0.16, and -0.50 ± 0.12 K decade-1 for the Stratospheric Sounding Unit (SSU) channels 3 (~40-50 km), 2 (~35-45 km), and 1 (~25-35 km), respectively. These are within the uncertainty bounds of the observed temperature trends from two reprocessed satellite datasets. In the lower stratosphere, the multi-model mean trend in global temperature for the Microwave Sounding Unit channel 4 (~13-22 km) is -0.25 ± 0.12 K decade-1 over 1979-2005, consistent with estimates from three versions of this satellite record. The simulated stratospheric temperature trends in CCMI models over 1979-2005 agree with the previous generation of chemistry-climate models. The models and an extended satellite dataset of SSU with the Advanced Microwave Sounding Unit-A show weaker global stratospheric cooling over 1998-2016 compared to the period of intensive ozone depletion (1979-1997). This is due to the reduction in ozone-induced cooling from the slow-down of ozone trends and the onset of ozone recovery since the late 1990s. In summary, the results show much better consistency between simulated and satellite observed stratospheric temperature trends than was reported by Thompson et al. (2012) for the previous versions of the SSU record and chemistry-climate models. The improved agreement mainly comes from updates to the satellite records; the range of simulated trends is comparable to the previous generation of models.

Chemistry–Climate Interactions of Stratospheric and Mesospheric Ozone in EMAC Long-Term Simulations with Different Boundary Conditions for CO2, CH4, N2O, and ODS

Abstract To evaluate future climate change in the middle atmosphere and the chemistry–climate interaction of stratospheric ozone, we performed a long-term simulation from 1960 to 2050 with boundary conditions from the Intergovernmental Panel on Climate Change A1B greenhouse gas scenario and the World Meteorological Organization Ab halogen scenario using the chemistry–climate model ECHAM5/MESSy Atmospheric Chemistry (EMAC). In addition to this standard simulation we performed five sensitivity simulations from 2000 to 2050 using the rerun files of the simulation mentioned above. For these sensitivity simulations we used the same model setup as in the standard simulation but changed the boundary conditions for carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone-depleting substances (ODS). In the first sensitivity simulation we fixed the mixing ratios of CO2, CH4, and N2O in the boundary conditions to the amounts for 2000. In each of the four other sensitivity simulations we fixed the boundary conditions of only one of CO2, CH4, N2O, or ODS to the year 2000. In our model simulations the future evolution of greenhouse gases leads to significant cooling in the stratosphere and mesosphere. Increasing CO2 mixing ratios make the largest contributions to this radiative cooling, followed by increasing stratospheric CH4, which also forms additional H2O in the upper stratosphere and mesosphere. Increasing N2O mixing ratios makes the smallest contributions to the cooling. The simulated ozone recovery leads to warming of the middle atmosphere. In the EMAC model the future development of ozone is influenced by several factors. 1) Cooler temperatures lead to an increase in ozone in the upper stratosphere. The strongest contribution to this ozone production is cooling due to increasing CO2 mixing ratios, followed by increasing CH4. 2) Decreasing ODS mixing ratios lead to ozone recovery, but the contribution to the total ozone increase in the upper stratosphere is only slightly higher than the contribution of the cooling by greenhouse gases. In the polar lower stratosphere a decrease in ODS is mainly responsible for ozone recovery. 3) Higher NOx and HOx mixing ratios due to increased N2O and CH4 lead to intensified ozone destruction, primarily in the middle and upper stratosphere, from additional NOx; in the mesosphere the intensified ozone destruction is caused by additional HOx. In comparison to the increase in ozone due to decreasing ODS, ozone destruction caused by increased NOx is of similar importance in some regions, especially in the middle stratosphere. 4) In the stratosphere the enhancement of the Brewer-Dobson circulation leads to a change in ozone transport. In the polar stratosphere increased downwelling leads to additional ozone in the future, especially at high northern latitudes. The dynamical impact on ozone development is higher at some altitudes in the polar stratosphere than the ozone increase due to cooler temperatures. In the tropical lower stratosphere increased residual vertical upward transport leads to a decrease in ozone.