Olaf Stein

Seasonal variability and trends of volatile organic compounds in the lower polar troposphere

Arctic, 82� 27 0 N, 62� 31 0 W). About 270 canister samples were analyzed covering the 7-year period with an average frequency of about one sample every 9 days. The mixing ratios of these volatile organic compounds (VOC) exhibit considerable variability, which can partly be described by systematic seasonal dependencies. The highest mixing ratios were always observed during winter. During spring, the mixing ratios decrease for some compounds to values near the detection limit. The amplitudes of the seasonal variability, the time of the occurrence of the maxima, and the relative steepness of the temporal gradients show a systematic dependence on OH reactivity. The steepest relative decrease is less than 1% d � 1 for methyl chloride, increasing to about 4% d � 1 for highly reactive VOC. Similarly, the highest relative increase rates vary between 0.5% d � 1 for VOC with low reactivity to 4% d � 1 for reactive VOC. With the exception of ethyne, toluene, and methyl chloride the concentrations of all measured VOC decrease during the studied period, although this decrease is not always statistically significant. In general, the largest changes were found for the most reactive VOC, although the seemingly random overall variability observed for these compounds results in substantial uncertainties. For the less reactive VOC (ethane, benzene, and propane) the average relative annual decrease rate is in the range of a few percent per year. Dichloromethane and tetrachloroethene showed a decrease of 4 and 14% yr � 1 , respectively. The average decrease rate for the other alkanes is in the range of some 10% yr � 1 , indicating a substantial change of emission rates during this period. A likely explanation is a reduction in VOC emissions in the area of the former Soviet Union, most likely Siberia, as a consequence of the recent major economic changes in this region. The measurements were compared with the results of chemical transport models’ simulations using the Emission Database for Global Atmospheric Research NMHC emission inventory. Although the model captures most of the main features of the shapes of the seasonal cycles of the NMHC, the results clearly show that model estimates are consistently too low compared to the observations. Most likely this is the consequence of an underestimate of the NMHC emission rates in the emission inventory. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; KEYWORDS: volatile organic compounds, halogenated compounds, Arctic troposphere, trends, seasonal variability Citation: Gautrois, M., T. Brauers, R. Koppmann, F. Rohrer, O. Stein, and J. Rudolph, Seasonal variability and trends of volatile organic compounds in the lower polar troposphere, J. Geophys. Res., 108(D13), 4393, doi:10.1029/2002JD002765, 2003.

Global reactive gases forecasts and reanalysis in the MACC project

The EU FP7 projects MACC (Monitoring Atmospheric Composition and Climate, 2009–2011) prepared for the operational Global Monitoring for Environment and Security (GMES) atmospheric core service on greenhouse gases, reactive gases and aerosols which is envisaged to start in 2014. This paper describes the data assimilation and modelling system which has been implemented for global monitoring of reactive gases in the troposphere and stratosphere. The MACC reactive gases system uses a coupling software to integrate the Model for Ozone And Related Tracers, version 3 (MOZART-3) chemistry transport model with the Integrated Forecast System (IFS) of the European Centre for Medium-range Weather Forecasts (ECMWF). The focus is placed on the tropospheric simulations with this MACC-IFS-MOZ model. The MACC reanalysis (2003–2010) and the forecasts performed in near real time (NRT) benefit from the multi-sensor approach for data assimilation of total columns, tropospheric columns and vertically resolved observations of ozone, CO and NO2. Daily biomass burning emissions are integrated in real time using the global fire assimilation system (GFAS) that was developed within MACC. Other emissions are taken from a state-of-the-art global inventory that was developed across several EU projects. The MACC reanalysis and tracer forecasts are routinely evaluated with ground-based and airborne in-situ observations and independent satellite retrieval products. We present the system set-up for reactive gases, give an overview on the service and technical developments during the project, and indicate how MACC global reactive gases products could provide information on non-CO2 greenhouse gases.

Seasonal and interannual variability of carbon monoxide based on MOZAIC observations, MACC reanalysis, and model simulations over an urban site in India

The spatial and temporal variations of carbon monoxide (CO) are analyzed over a tropical urban site, Hyderabad (17°27′N, 78°28′E) in central India. We have used vertical profiles from the Measurement of ozone and water vapor by Airbus in-service aircraft (MOZAIC) aircraft observations, Monitoring Atmospheric Composition and Climate (MACC) reanalysis, and two chemical transport model simulations (Model for Ozone And Related Tracers (MOZART) and MRI global Chemistry Climate Model (MRI-CCM2)) for the years 2006–2008. In the lower troposphere, the CO mixing ratio showed strong seasonality, with higher levels (>300 ppbv) during the winter and premonsoon seasons associated with a stable anticyclonic circulation, while lower CO values (up to 100 ppbv) were observed in the monsoon season. In the planetary boundary layer (PBL), the seasonal distribution of CO shows the impact of both local meteorology and emissions. While the PBL CO is predominantly influenced by strong winds, bringing regional background air from marine and biomass burning regions, under calm conditions CO levels are elevated by local emissions. On the other hand, in the free troposphere, seasonal variation reflects the impact of long-range transport associated with the Intertropical Convergence Zone and biomass burning. The interannual variations were mainly due to transition from El Nino to La Nina conditions. The overall modified normalized mean biases (normalization based on the observed and model mean values) with respect to the observed CO profiles were lower for the MACC reanalysis than the MOZART and MRI-CCM2 models. The CO in the PBL region was consistently underestimated by MACC reanalysis during all the seasons, while MOZART and MRI-CCM2 show both positive and negative biases depending on the season.

Lagrangian transport simulations of volcanic sulfur dioxide emissions: Impact of meteorological data products

Sulfur dioxide (SO2) emissions from strong volcanic eruptions are an important natural cause for climate variations. We applied our new Lagrangian transport model Massive-Parallel Trajectory Calculations to perform simulations for three case studies of volcanic eruption events. The case studies cover the eruptions of Grímsvötn, Iceland, Puyehue-Cordón Caulle, Chile, and Nabro, Eritrea, in May and June 2011. We used SO2 observations of the Atmospheric Infrared Sounder (AIRS/Aqua) and a backward trajectory approach to initialize the simulations. Besides validation of the new model, the main goal of our study was a comparison of simulations with different meteorological data products. We considered three reanalyses, i.e., ERA-Interim, Modern-Era Retrospective Analysis for Research and Applications (MERRA), and National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) Reanalysis Project as well as the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis. Qualitatively, the SO2 distributions from the simulations compare well not only with the AIRS data but also with Cloud-Aerosol Lidar with Orthogonal Polarization and Michelson Interferometer for Passive Atmospheric Sounding aerosol observations. Transport deviations and the critical success index (CSI) are analyzed to evaluate the simulations quantitatively. During the first 5 or 10 days after the eruptions we found the best performance for the ECMWF analysis (CSI range of 0.25–0.31), followed by ERA-Interim (0.25–0.29), MERRA (0.23–0.27), and NCAR/NCEP (0.21–0.23). High temporal and spatial resolution of the meteorological data does lead to improved performance of Lagrangian transport simulations of volcanic emissions in the upper troposphere and lower stratosphere.

On the use of MOZAIC-IAGOS data to assess the ability of the MACC reanalysis to reproduce the distribution of ozone and CO in the UTLS over Europe

MOZAIC-IAGOS data are used to assess the ability of the MACC reanalysis (REAN) to reproduce distributions of ozone (O3) and carbon monoxide (CO), along with vertical and inter-annual variability in the upper troposphere/lower stratosphere region (UTLS) over Europe for the period 2003–2010. A control run (CNTRL, without assimilation) is compared with the MACC reanalysis (REAN, with assimilation) to assess the impact of assimilation. On average over the period, REAN underestimates ozone by 60 ppbv in the lower stratosphere (LS), whilst CO is overestimated by 20 ppbv. In the upper troposphere (UT), ozone is overestimated by 50 ppbv, while CO is partly over or underestimated by up to 20 ppbv. As expected, assimilation generally improves model results but there are some exceptions. Assimilation leads to increased CO mixing ratios in the UT which reduce the biases of the model in this region but the difference in CO mixing ratios between LS and UT has not changed and remains underestimated after assimilation. Therefore, this leads to a significant positive bias of CO in the LS after assimilation. Assimilation improves estimates of the amplitude of the seasonal cycle for both species. Additionally, the observations clearly show a general negative trend of CO in the UT which is rather well reproduced by REAN. However, REAN misses the observed inter-annual variability in summer. The O3–CO correlation in the Ex-UTLS is rather well reproduced by the CNTRL and REAN, although REAN tends to miss the lowest CO mixing ratios for the four seasons and tends to oversample the extra-tropical transition layer (ExTL region) in spring. This evaluation stresses the importance of the model gradients for a good description of the mixing in the Ex-UTLS region, which is inherently difficult to observe from satellite instruments.

TROPOSPHERIC CHEMISTRY AND COMPOSITION | Aliphatic Hydrocarbons

Synopsis During the last decades it has been recognized that organic trace gases other than methane play an important role in the chemistry of the troposphere. Aliphatic nonmethane hydrocarbons (NMHCs) are one of the major groups among the wide range of compounds that constitute nonmethane volatile organic compounds (VOCs). Although the total global emission rate of aliphatic NMHC is only a small fraction of all VOC emissions, the uneven spatial and temporal distribution of aliphatic hydrocarbon emissions combined with their high reactivity makes them important contributors to atmospheric chemical reactions in areas with strong emissions such as urban and industrialized regions or areas with strong biomass burning activities. Aliphatic hydrocarbons are also valuable tracers for identifying important atmospheric processes and trace gas sources.

Coupling Global Atmospheric Chemistry Transport Models to ECMWF Integrated Forecasts System for Forecast and Data Assimilation Within GEMS

The paper presents the implementation of a coupled forecast and assimilation system developed within the subproject on Global Reactive Gases (GRG) of the GEMS-project (Global and regional Earth-system (Atmosphere) Monitoring using Satellite and in-situ data, FP6).

Climate change reduces warming potential of nitrous oxide by an enhanced Brewer‐Dobson circulation

The Brewer-Dobson circulation (BDC), which is an important driver of the stratosphere-troposphere exchange, is expected to accelerate with climate change. One particular consequence of this acceleration is the enhanced transport of nitrous oxide (N2O) from its sources at the Earths surface toward its main sink region in the stratosphere, thus inducing a reduction in its lifetime. N2O is a potent greenhouse gas and the most relevant currently emitted ozone-depleting substance. Here we examine the implications of a reduced N2O lifetime in the context of climate change. We find a decrease in its global warming potential (GWP) and, due to a decline in the atmospheric N2O burden, also a reduction in its total radiative forcing. From the idealized transient global warming simulation we can identify linear regressions for N2O sink, lifetime, and GWP with temperature rise. Our findings are thus not restricted to a particular scenario.

Use of GOME Measurements for the Examination of the Nitrogen Oxide Budget in the Troposphere

Ozone in the troposphere is controlled by stratospheric-tropospheric exchange (STE) and in-situ production which depends on the concentration of precursors such as the nitrogen oxides NOX. Due to the short tropospheric lifetime of NOX, its global distribution strongly corresponds to the distribution of emissions. We want to quantify the relative contributions and the geographic distributions of individual NOX emission sources using a variety of satellite data. Nitrogen dioxide NO2 measured by the GOME satellite has been compared to night-time light emissions observed from space. These light emissions can serve as a proxy for emissions of NOX from fossil fuel combustion. It turns out that the light density at the earth’s surface shows a better correlation with tropospheric NO2 measured by GOME than the estimated anthropogenic emissions in the EDGAR database which are widely used in global chemistry models. Recently satellite datasets of global lightning flash frequencies (LIS/OTD) and fire counts (ATSR) became available. With the satellite datasets of light density, lightning intensity, fire counts, and NO2 column density we hope to improve the current knowledge of nitrogen oxide emissions.