This paper explains a new way to evaluate simulated lower-stratospheric water vapor. We use a multivariate linear regression to predict 21st century lower stratospheric water vapor within 12 chemistry climate models using tropospheric warming, the Brewer–Dobson circulation, and the quasi-biennial oscillation as predictors. This methodology produce strong fits to simulated water vapor, and potentially represents a superior method to evaluate model trends in lower-stratospheric water vapor.

We present an intercomparison of temperatures and horizontal winds of five meteorological data sets (ECMWF operational analysis, ERA-Interim, MERRA, MERRA-2, and NCEP/NCAR) in the Antarctic lower stratosphere. The assessment is based on 19 superpressure balloon flights during the Concordiasi field campaign in September 2010 to January 2011. The balloon data are used to successfully validate trajectory calculations with the new Lagrangian particle dispersion model MPTRAC.

We measured the relationship between volcanic aerosol and trace gases in the stratosphere using the OSIRIS and MIPAS satellite instruments between 2002 and 2014. We found that levels of stratospheric NO₂ and N₂O₅ both decreased significantly in the presence of volcanic aerosol. These decreases were consistent with the modeling results.

In the Netherlands 9 W m⁻² more solar radiation falls on the surface today than 50 years ago. Often this increase, which has also been detected in surrounding western Europe, has been attributed to decreasing air pollution due to improved regulatory practices. However, over the Netherlands clouds play an important but ambiguous role. Cloud cover has increased but have become optically thinner as well. Here, the impact of clouds on radiation is in fact more important than that of air pollution.

This study analyses multi-year observations of atmospheric particles from five Arctic sites. These particles affect climate and air quality. The main factors that control the distinct annual cycle in the concentration of these particles are long-range transport and precipitation. The former brings pollution from the Asian sector – mostly during winter/spring – while the latter clears the air in summer/autumn. However, there are consistent differences between the sites due to regional factors.

This study provides quantitative information regarding the source contributions of the major non-methane volatile organic compound sources in the Kathmandu Valley. Combining high-resolution in situ NMVOC data and model analyses, we show that REAS v2.1 and EDGAR v4.2 emission inventories underestimate the contribution of traffic and do not take the contribution of brick kilns into account. Furthermore, REAS v2.1 overestimates the contribution of residential biofuel use and industries.

Ceilometer measurements taken in the Kathmandu Valley, Nepal, were used to study the temporal and spatial evolution of the mixing layer height in the valley. This provides important information on the vertical structure of the atmosphere and can thus also help to understand the mixing of air pollutants (e.g. black carbon) in the valley. The seasonal and diurnal cycles of the mixing layer were found to be highly dependent on meteorology and mainly anticorrelated to black carbon concentrations.

An analysis based on physical conservation law demonstrates that surface–atmosphere exchanges include a non-diffusive component. This implies the need to revise flux gradient relationships including eddy diffusivities in micrometeorology and stomatal conductances in plant physiology.

Man's activities have greatly increased the amount of nitrogen emitted into the atmosphere. Some of this nitrogen is transported to the world's oceans, where it may affect microscopic marine plants and cause ecological problems. The huge size of the oceans makes direct monitoring of nitrogen inputs impossible, so computer models must be used to assess this issue. We find that current models reproduce observed nitrogen deposition to the oceans reasonably well and recommend future improvements.

Previous investigations into Chinese urban air quality have been hampered by a lack of available data. In this work we present a new statistical modelling technique, in which sparse ground-based measurements of nitrogen dioxide (NO₂) are combined with satellite data and other parameters (e.g. road networks) to create high-resolution maps of daily surface NO₂ concentrations over Hong Kong. These maps can be used to estimate population exposure, and to identify at-risk groups.

We showed the large contribution of different source regions in Asia to the recent increasing trend in surface ozone over Japan by using a global chemical transport model. China accounted for the largest part of the increasing trend, not only through the domestic ozone production (36 %) but also the ozone production in the adjacent countries due to the ozone precursors emitted in China (10 %). Other factors such as temporal change in climate and methane concentration were also investigated.

We present the first long-term organic aerosol source apportionment in an environment influenced by anthropogenic emissions including biomass burning and industrial processes and an active photochemistry. Online and offline aerosol mass spectrometry were used to characterize these emissions and their transformation. Measurements of organic markers provided insights into the origin of biomass smoke in this area, with different seasonal contributions from domestic heating and agricultural burning.

We report increasing levels of alkyl nitrates in the Northern Hemisphere atmosphere between 1960 and the mid-1990s. These increases are symptomatic of large-scale changes to the chemical composition of the atmosphere, particularly with regards to the amounts of short-lived, reactive species. The observed increases are likely driven by increasing levels of nitrogen oxides. These changes have direct implications for the lifetimes of climate-relevant species in the atmosphere, such as methane.

The ACCMIP ensemble ozone simulations are evaluated by a state-of-the-art multi-constituent chemical reanalysis. The reanalysis product provides comprehensive and unique information on the weakness of the individual models and multi-model mean. The differences are less evident with the current sonde network, which is shown to provide biased regional and monthly ozone statistics. The evaluation results have implications for ozone radiative forcing and the response of chemistry to climate.

We present the first carbon dioxide (CO₂) and methane (CH₄) measurements from an extensive surface network as part of the Los Angeles Megacity Carbon Project. We describe methods that are essential for understanding carbon fluxes from complex urban environments. CO₂ and CH₄ levels are spatially and temporally variable, with urban sites showing significant enhancements relative to background. In 2015, the median afternoon enhancement near downtown Los Angeles was ~15 ppm CO₂ and ~80 ppb CH₄.

This study analyzes at which aerosol radius the mass growth leading to activation switches from diffusion to collection, marking the limit of traditional Köhler activation theory. It is found that collection becomes increasingly important for aerosols larger than 0.1 µm in dry radius and is responsible for all activations of aerosols larger than 1.0 µm. A novel particle-based cloud modeling approach is applied, in which activation can be represented without parameterizations.

Gas-phase cyclic volatile methyl siloxanes and their oxidation products, which are likely precursors to secondary organic aerosol, were modeled using an atmospheric transport model over North America. Typical concentrations, spatial patterns, seasonal variability, and vertical profiles were quantified. Urban parent compound concentrations were sensitive to transport factors, while rural parent and oxidized product concentrations were sensitive to large-scale seasonal variability in OH.

Atmospheric methane simulations in the Arctic have been made for 2012 and compared to continuous observations at six measurement sites. All methane sources significantly affect the measurements at all stations, at least at the synoptic scale, except for biomass burning. An appropriate modelling framework combined with continuous observations of atmospheric methane enables us to gain knowledge on regional methane sources, including those which are usually poorly represented, such as freshwater.

This work focus on the distribution of dust particles emitted in western Africa and having consequences on human health and marine ecosystems. The understanding of their fate requires a better understanding of the processes governing their variability. Using satellite observations and ground measurements, we present the seasonality of their distribution and explain the processes responsible for this distribution as well as their transition from the African continent towards the Atlantic Ocean.

The emission and formation of gaseous organic acids from the oil sands industry in Canada is explored through aircraft measurements directly over and downwind wind of industrial facilities. Results demonstrated that the formation of organic acids through atmospheric chemical reactions dominated over the direct emissions from mining activities but could not be explicitly modeled. The results highlight the need for improved understanding of photochemical mechanisms leading to these species.

We evaluate global ozone–carbon monoxide (O₃–CO) correlations in a chemistry and transport model during July–August with TES-Aura satellite observations and examine the sensitivity of model simulations to input meteorological data and emissions. Results show that O₃–CO correlations may be used effectively to constrain the sources of regional tropospheric O₃ in global 3-D models, especially for those regions where convective transport of pollution plays an important role.

We present quantitative condensed-phase diffusivity measurements of a volatile organic (tetraethylene glycol) in highly viscous single aerosol particles (aqueous sucrose). The condensed-phase diffusivity exhibits a strong temperature and humidity dependence. Our results suggest that diffusion limitations of volatile organics in highly viscous organic aerosol may severely impact gas–particle partitioning under cold and dry conditions.

A ground-based counterflow virtual impactor coupled with a single-particle aerosol mass spectrometer (SPAMS) was used to assess the mixing state of individual cloud residue particles. Abundant aged EC cloud residues that internally mixed with inorganic salts were found in air masses from northerly polluted areas. K-rich cloud residues significantly increased within southwesterly air masses. This study increases our understanding of the impacts of aerosols on cloud droplets in southern China.

This study presents impact of cirrus cloud horizontal heterogeneity on simulated thermal infrared brightness temperatures at the top of the atmosphere for spatial resolutions ranging from 50 m to 10 km. The cirrus is generated by the 3DCLOUD code and the radiative transfer by the 3DMCPOL code. Brightness temperatures are mostly impacted by the horizontal transport effect and plane-parallel bias at high and coarse spatial resolutions, respectively, with a minimum around 100 m–250 m.

The viscosities of four polyols and three saccharides mixed with water were determined. The results from the polyol studies suggest viscosity increases by 1–2 orders of magnitude with the addition of an OH functional group to a carbon backbone. The results from the saccharide studies suggest that the viscosity of highly oxidized compounds is strongly dependent on molar mass and oligomerization of highly oxidized compounds in atmospheric SOM could lead to large increases in viscosity.

We revisit the proxies/uncertainties for the ¹³C/¹²C ratios of emissions of reactive C into the atmosphere. Our main findings are (i) a factor of 2 less uncertain estimate of tropospheric CO surface sources δ¹³C, (ii) a confirmed disagreement between the bottom-up and top-down ¹³CO-inclusive emission estimates, and (iii) a novel estimate of the δ¹³C signatures of a range of NMHCs/VOCs to be used in modelling studies. Results are based on the EMAC model emission set-up evaluated for 2000.

We introduce a novel 3-D method of measuring atmospheric gravity waves, based around a 3-D Stockwell transform. Our method lets us measure new properties, including wave intrinsic frequencies and phase and group velocities. We apply it to data from the AIRS satellite instrument over the Southern Andes for two consecutive winters. Our results show clear evidence that the waves measured are primarily orographic in origin, and that their group velocity vectors are focused into the polar night jet.

To obtain knowledge about sea-salt chemistry in polar regions, we made simultaneous measurements and sampling of aerosols, frost flowers, and brine around northwestern Greenland during winter–spring. Our results show sea-salt enrichment in frost flowers and snow. Also, the fractionated sea-salt particles were suspended in the atmosphere over sea-ice areas. From the field evidence and results from earlier studies, we propose and describe sea-salt cycles in seasonal sea-ice areas.

We have studied the optical properties of ash-rich and sulfate-rich volcanic aerosols by analysing satellite observations of three different volcanic eruptions. Our results indicate that ash particles have distinctive optical properties when compared to sulfates. We expect our results will improve space-borne lidar detection of volcanic aerosols and provide new insight into their interaction with the atmosphere and solar radiation.

Arctic temperatures have risen faster than the global average, causing the depth of melting of the frozen ground to increase. Previously frozen organic carbon, once exposed to air, water, and microbes, is turned into carbon dioxide and methane, both of which are important greenhouse gases. Due to the large and varied surface area of the Arctic and the difficulty of making measurements there we use a low flying aircraft (<25 m) to measure the amount of methane released from different regions.