This paper describes the process of the transfer of water molecules between liquid and the ice during the early stages of ice formation. Using concepts of nonreversible thermodynamics, it is shown that the activation energy can be defined in terms of the bulk self-diffusivity of water and the probability of interface transfer. The application of this model to classical nucleation theory shows good agreement of measured nucleation rates with experimental results for temperatures as low as 190K.

We present the longest (1998 to 2013) cirrus cloud climatology over a tropical station using a ground-based lidar. A statistically significant increase is found in the altitude of sub-visible cirrus clouds. Also a systematic shift from thin to sub-visible cirrus cloud type is observed. Ground-based lidar is found to detect more number of sub-visible cirrus clouds than space-based lidar. These findings have implications to global warming and stratosphere-troposphere water vapour exchange studies.

We find that argon/nitrogen ratios of trapped air in the GISP2 ice core on “gas ages” are significantly negatively correlated with accumulation rate changes over the past 6000 years. Lines of evidence indicate that changes in overloading pressure at bubble closeoff depths induced the gas fractionation in closed bubbles. Further understanding of the fractionation processes may lead to a new proxy for the past temperature and accumulation rate.

A comprehensive suite of instruments was used to quantify the emissions of over 200 organic and inorganic gases from 56 laboratory burns of 18 different biomass fuel types common in the southeastern, southwestern, or northern United States. Emission ratios relative to carbon monoxide (CO) are used to characterize the composition of gases emitted by mass; OH reactivity; and potential secondary organic aerosol (SOA) precursors for the three different U.S. fuel regions presented here.

The aim of this paper is to present a full-year analysis of simultaneous measurements of ozone, black carbon, and aerosol number concentration at Paknajol, in the Kathmandu Valley, one of the global “hot spots” in terms of air pollution. Results indicate persisting poor air quality conditions throughout the measurement period, and suggest that the pollutants' variability is mainly driven by local pollution source activity, local- and large-scale dynamics, photochemistry, and vegetation fires.

Secondary organic aerosol (SOA) is an important pollutant formed from megacity emissions at a regional scale. An original method based on ratios of different pollutants is used to specifically validate the aerosol scheme (the volatility basis set approach) within a CTM. The method is applied to airborne measurements performed within the Paris plume during the MEGAPOLI summer campaign. Simulations indicate that SOA of anthropogenic origin has a significant impact on regional air quality.

The role of low-volatility organics in new particle formation (NPF) in the atmosphere is assessed. An empirical formulation in which formation rate is a function of the concentrations of sulfuric acid and low-volatility organics significantly overpredicts NPF in the summer. Two different schemes predict quite different nucleation rates (including their spatial patterns), concentrations of cloud condensation nuclei, and aerosol first indirect radiative forcing in North America.

The Monitoring Atmospheric Composition and Climate project (MACC) operationally produces global analyses and forecasts of reactive gases and aerosol fields. We have investigated the ability of the model to simulate concentrations of reactive gases (carbon monoxide, nitrogen dioxide and ozone) between 2009 and 2012. The model reproduced reactive gas concentrations with consistent quality, however, with a seasonally dependent bias compared to surface and satellite observations.

We find a strong regional element to the uplift of CHBr3 from the ocean to the upper troposphere and lower stratosphere. The strongest uplift occurs when the largest emission and the most intense convection are co-located which is over the Maritime Continent in northern winter. Estimates of CHBr3 emissions based on aircraft measurements will be sensitive to where the available aircraft campaigns took place.

At night, concentrations of methane and other trace gases in the near-surface atmosphere increase due to limited turbulent mixing and confluence of cold air from valley slopes towards the valley bottom. Here we used a tethered balloon sounding system to obtain time-height profiles of methane concentrations from which we compute methane emissions. These flux estimates serve as the first experimental validation of Swiss agricultural methane emissions at the farm scale.

This paper presents the first study of the hygroscopic properties of limonene derived organosulfates (L-OS 250). The results showed that L-OS 250 particles are weakly hygroscopic and able to activate into cloud droplets. Particles of L-OS 250 mixed with ammonium sulfate were much more hygroscopic than expected from model parametrizations and the ZSR mixing rule, indicating that solubility and non-ideal droplet interactions could be important for the hygroscopic properties of the mixed particles.