This work describes the chemical and physical characterization of very small (< 100 nm diameter) particles in the marine atmosphere. We show that sea salt is present even at very small sizes and present evidence that organic species are important contributors to apparent new particle formation events over the ocean.

The complexity of the physical and chemical processes effectively turns global aerosol models into black boxes. In an attempt to lift the veil, we present a detailed budget of process contributions (emissions, nucleation, sulfate condensation, coagulation, aging, deposition) in ECHAM5.5-HAM2 across varying length- and timescales. We show a clear hierarchy exists in process importance, that can be used in improving and simplifying the model and for understanding discrepancies with observation.

Black carbon in snow lowers its albedo, increasing the absorption of sunlight, leading to positive radiative forcing, climate warming and earlier snow-melt. A series of recent studies have used prescribed rates of black carbon deposition to snow to assess the climate effects of black carbon in snow. Here we show that the use of prescribed deposition fluxes in these model studies leads to high biases in snow BC concentrations, caused by the decoupling of BC and snow deposition to the surface.

New parameterizations for the sea spray aerosol source flux and its organic fraction were incorporated into a global aerosol-climate model. The emissions of sea salt were considerably less than previous estimates. This study demonstrates that sea spray aerosol may actually decrease the number of cloud droplets, which has a warming effect on climate. Overall, sea spray aerosol was predicted to have a global cooling effect due to the scattering of solar radiation from sea spray aerosol particles.

Tamanrasset, in the heart of the Sahara, is a key site for aerosol research. The analysis of more than 2 years (2006-2009) of AERONET and KCICLO-corrected sun photometer measurements shows that atmospheric aerosols at Tamanrasset are modulated by the Convective Boundary Layer leading to pure Saharan dust conditions (April-September) and very clear sky conditions (November-February). Dust potential sources and anthropogenic fine aerosols arriving at Tamanrasset are also identified.

Water uptake of ambient particles was measured by 2 independent techniques at a wide range of locations between 2007 and 2013. The agreement between the techniques was mixed and hence the number of potential cloud seeds calculated from the measurements frequently showed discrepancies. Whilst there is sensitivity to how well we measure the size of the particles, much of the difference depends on how the particles behave when exposed to moisture in the different techniques (and in the atmosphere).

We report observations of nitric acid and peroxynitric acid, in coastal Antarctica during winter. During winter, it is dark 24h per day, so there is no influence of sunlight on atmospheric composition. We show that observed variability in concentrations is highly correlated with changes in temperature. We derive enthalpies of adsorption and show they are consistent with those derived in laboratory studies. The Antarctic, during winter, is an ideal natural laboratory to study air-snow exchange.

Secondary organic aerosols (SOA), produced through oxidation processes, constitute a large part of the global organic aerosol load and affect the climate. We found that the modeled mass of SOA was highly dependent on how the oxidation processes were explained in models. The results indicated that it was especially important to get the volatility distribution of the products from the first oxidation step right and that fragmentation during the oxidation process played an important role.

This paper reviews aerometric measurements from Centreville, Alabama. The measurements show annual trends with air pollution emissions from 1999 to 2013. They provide a context for observations from 1 June to 15 July 2013 supporting the Southern Oxidant and Aerosol Study. An important goal of this experiment was to advance knowledge of aerosols produced in the atmosphere from precursors. The observations were in moist and warm conditions with the lowest gas and particle concentrations recorded.

This study examines the characteristics of the microphysics and macrophysics of water clouds from East Asia to the North Pacific, using data from CloudSat and MODIS retrievals. We demonstrate regional and seasonal characteristics of the cloud vertical structure and found a difference in the “contoured frequency by optical-depth diagram” (CFODD) between the pristine oceanic area and the polluted land area, implying aerosol-–cloud interaction.

This paper presents a new operational CO2 forecast product as part of the Copernicus Atmospheric Services suite of atmospheric composition products, using the state-of-the-art numerical weather prediction model from the European Centre of Medium-Range Weather Forecasts. The evaluation with independent observations shows that the forecast has skill in predicting the synoptic variability of CO2. The online simulation of CO2 fluxes from vegetation contributes to this skill.

What role do forests play in determining the concentration (and composition) of climate-relevant aerosol particles? This study seeks to address two aspects of this question. Firstly, we document high in-canopy removal of recently formed particles. Then we show evidence that growth rates of particles are a function of soil water availability via a reduction in canopy emissions of gases responsible for particle growth to climate-relevant sizes during drought conditions.

Several biases in the representation of clouds in the stratocumulus regime in the ECHAM6-HAM2 global climate model were found by evaluating the model in the stratocumulus cloud regime. Simulations with changes in model resolution and physics to better represent clouds and aerosol in the stratocumulus regime show that the human influence on clouds and thus climate by emission of aerosol particles is sensitive to the representation of (stratocumulus) clouds.