LIVAS is a 3-D multi-wavelength global aerosol and cloud optical database optimized for future space-based lidar end-to-end simulations of realistic atmospheric scenarios as well as retrieval algorithm testing activities. The global database is based on CALIPSO observations at 532nm, while for the conversion at 355nm EARLINET data are utilized. Hide

We discuss the representation of wildfire emission heights in global climate models. Our implementation of a simple, semi-empirical plume height parametrization in the aerosol-climate model ECHAM6-HAM2 shows reasonable agreement with observations and with a more complex plume rise model. In contrast, prescribed emission heights, which do not consider the intensity of individual fires, fail to adequately simulate global plume height patterns. Diurnal and seasonal cycles are of minor importance. Hide

Global aerosol-climate models usually prescribe wildfire emission injections at fixed atmospheric levels. Here, we quantify the impact of prescribed and parametrized emission heights on aerosol long-range transport and radiation. For global emission height changes of 1.5-3.5km, we find a top-of-atmosphere radiative forcing of 0.05-0.1Wm-2. Replacing prescribed emission heights by a simple plume height parametrization only marginally improves the model performance in aerosol optical thickness. Hide

We present a new way to formulate the quantum yields of formaldehyde with several advantages. The formulation is simpler and has fewer parameters than those used so far, and the parameters have a physical meaning. It provides a template for the formulation of other quantum yields, e.g., of the isotopologues of formaldehyde. In addition, we offer a careful review of published measurements. It is also advantageous that the formulation can easily be modified to include temperature effects. Hide

The ion-ion recombination coefficient was measured at different temperatures, relative humidities and concentrations of ozone and sulfur dioxide. The experiments were carried out using the CLOUD chamber at CERN. We observed a strong dependency on temperature and on relative humidity, which has not been reported previously. No dependency of the ion-ion recombination coefficient on ozone concentration was observed and a weak variation with sulfur dioxide concentration was also observed. Hide

We assess the impact of biogenic emissions on CO and HCHO in the Southern Hemisphere (SH), with simulations using different emission inventories. Differences in biogenic emissions result in large differences on modelled CO in the source and the remote regions. Substantial inter-model differences exist. Models significantly underestimate observed HCHO columns in the SH, suggesting missing sources in the models. Differences in the CO/OH/CH4 chemistry lead to differences in HCHO in remote regions. Hide

The effect of water uptake (hygroscopicity) on aerosol light scattering properties is generally lower for boreal aerosol due to the dominance of organic substances. A columnar optical closure study using ground-based and airborne measurements of aerosol optical, chemical and microphysical properties was conducted and the implications and limitations are discussed. Hide

PBL processes are important for weather, climate, and tracer transport and concentration. In the GEOS-5 AGCM, the PBL depth is used in the calculation of turbulent mixing. This study analyzes the impact of using different PBL depth definitions in this calculation. Near surface wind speed differences modify Saharan dust on the order of 1e-4kg m-2. CO surface concentrations are modified by up to 20 ppb over biomass burning regions. Instantaneous CO2 differences are on the order of 10 ppm. Hide

Nitrate and ammonium ice core records from Lomonosovfonna, Svalbard, indicated anthropogenic pollution from Eurasia as major source during the 20th century. In pre-industrial times nitrate is correlated with methane sulfonate, which we explain with a fertilising effect, presumably triggered by enhanced atmospheric nitrogen input to the ocean. Eurasia was likely the main source area also of pre-industrial nitrate, but for ammonium, biogenic emissions from Siberian boreal forests were dominant. Hide

Varotsos et al. (Theor. Appl. Climatol., 114, 725–727, 2013) found that the solar ultraviolet (UV) wavelengths exhibit 1/f-type power-law correlations. In this study, we show that the residues of the spectral solar incident flux with respect to the Planck law over a wider range of wavelengths (i.e. UV-visible) have a scaling regime too. Hide

Year-long comprehensive characterization of ambient aerosol was performed in both rural and urban sites in the southeastern US as part of Southeastern Center of Air Pollution and Epidemiology (SCAPE) study and Southeastern Oxidant and Aerosol Study (SOAS). Three independent methods were applied to estimate the concentration of particle-phase organic nitrates. The spatial distribution of organic aerosol is investigated by comparing simultaneous HR-ToF-AMS and ACSM measurements at different sites. Hide

Measurements of the photolysis rates which drive production of OH from ozone are reported for Cape Grim, a "clean-air" site in the southern midlatitudes. This remote maritime site sits in the Southern Ocean, a region of the globe which is little studied. From the 6 years of data the dependence of this photolysis on solar zenith angle and stratospheric ozone is determined. Included with the reported values is an estimate of the uncertainties in these measurements. Hide

Most research on the relationship between aerosol and closed/open cell transitions tends to focus on the closed to open transition. Here we address the two-way transition between closed and open cellular states using a cloud resolving model. We find inherent asymmetry in the transitions and explain the source of the asymmetry. Results are supported by a dynamical system analogue to the full system. Hide

Surface erythemal UV data from the Ozone Monitoring Instrument (OMI) are validated for high northern latitudes (Arctic and Scandinavia) using ground-based measurements. The bias in OMI data caused by incorrect assumptions of the surface albedo are quantified and the mechanism that causes this bias is discussed. Methods to improve the accuracy of OMI data products are presented. Hide

Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of plants as the major source and the reaction with OH as the major sink, global methanol budgets diverge considerably in terms of source/sink estimates. Here we present micrometeorological methanol flux data from eight sites in order to provide a first cross-site synthesis of the terrestrial methanol exchange. Hide

Sensitivities of Lagrangian cirrus modelling on input data uncertainties have been examined. We found a strong dependence on the temporal resolution of the trajectories and underlying numerical weather prediction (NWP) data as well as on the specific moisture content. Furthermore, we found a large day-to-day variability in the vertical wind spectrum, demonstrating the necessity to apply NWP models with high spatial and temporal resolution for Lagrangian cirrus modelling. Hide

A novel model of the absorption of radiation by ozone in the UV bands [283, 307]nm and [307, 328]nm yields improvements in the modeling of the transmissivity in these bands. This model is faster than detailed spectral calculations and is as accurate with maximum errors of respectively 0.0006 and 0.0143. How to practically implement this new parameterization in a radiative transfer model is discussed for the case of libRadtran. Hide

Long-term 28-year variability of Saharan dust export to the Atlantic is correlated with large-scale meteorology in North Africa, particularly with the intensity of the Saharan high to tropical low dipole-like pattern, the so-called North African Dipole. Variability in the dipole intensity is connected with winds, monsoon rain band and latitudinal shifts of the Saharan air layer. Variability in the dipole intensity suggests connections with ENSO and the Sahel drought. Hide

In this study, we have developed a modified micrometeorological gradient method (MGM), although based on existing micrometeorological theory, to estimate O3 dry deposition fluxes over a forest canopy using concentration gradients between a level above and a level below the canopy top. The new method provides an alternative approach in monitoring/estimating long-term deposition fluxes of similar pollutants over tall canopies and is expected to be useful for the scientific community. Hide

Laboratory chamber studies were conducted to investigate the formation of secondary organic aerosol from β-pinene oxidation by nitrate radicals. These experiments probed the effects of peroxy radical fate and relative humidity on the mass and chemical composition of secondary organic aerosol formed from nighttime chemistry. Results from this study were used to evaluate the contributions of NO3+monoterpene reaction to ambient organic aerosol recently measured in the southeastern United States. Hide

Fine volcanic ash can influence cloud glaciation and, therefore, global climate. In this work we examined the heterogeneous ice nucleation properties of three distinct types of volcanic ash. We find that, in contrast to previous studies, these volcanic ash samples have different ice nucleation properties in the immersion mode. In the deposition mode, however, they nucleate ice with similar efficiency. We show that this behavior may be due to their mineralogy. Hide

This work analyzes the chemical composition of blowing snow collected over first-year Antarctic sea ice to assess its role in bromine activation during the polar sunrise. We found lofted snow to be depleted in Br- relative to Cl- by proportionally increasing amounts with height. This is the first study to use field data to substantiate modeling results implicating blowing snow as the location for initial halogen activation. We also found lofted snow to be depleted in SO4 and enriched in NO3. Hide

Wet scavenging generates differences between the aerosol properties in clear-sky scenes (observed by satellites) and cloudy scenes, leading to different aerosol-precipitation relationships in satellite data and global models. Convective systems usually draw in air from clear-sky regions, but global models have difficulty separating this aerosol from the aerosol in cloudy scenes within a model gridbox. This may prevent models from reproducing the observed aerosol-precipitation relationships. Hide

The afternoon-evening transition (AET) in the atmospheric boundary layer has been studied in an integrated approach using 3 years of tower, sodar and wind profiler measurements. Such a long-term data set has been used for the first time to understand the behavior of AET. It allowed us to study the seasonal variation. In contrast to the common belief that the transition evolves from bottom to top, the present study clearly showed that the start time of transition follows top-to-bottom evolution. Hide

This work studied more than 10 years of measurements of aerosol optical depths (AODs) made for 50 sites of CARSNET compiled into a climatology of aerosol optical properties for China. It lets us see a detailed full-scale description of AOD observations over China. The results would benefit us a lot in comprehending the temporal and special distribution aerosol optical property over China. Also the data would be valuable to communities of aerosol satellite retrieval, modelling, etc. Hide

This manuscript aims to answer the following question: which of the existing sites engaged in upper-air temperature measurements are best located to detect expected future trends within the shortest time possible? To do so, we explore one objective method for selecting the optimal locations for detecting projected 21st century trends and then demonstrate a similar technique for objectively selecting optimal locations for detecting expected future trends in total column ozone. Hide

Based on spectral and wavelet analyses, along with a diagnosis of the polarization relations, this study analyzes in situ airborne measurements from the 2008 Stratosphere-Troposphere Analyses of Regional Transport (START08) experiment to characterize gravity waves in the extratropical upper troposphere and lower stratosphere (ExUTLS) region. The focus is on the second research flight (RF02), which was dedicated to probing gravity waves associated with strong upper-tropospheric jet-front systems. Hide

The efficacy of emission policies is explored by coarse resolution modeling applications. These were shown to be biased, overestimating that efficacy indicated in simulations with refined resolution. In order to improve our assessments, we need to quantify those biases. In this study we show that the ozone bias of the coarse run is reduced by 40% by adopting higher resolution emissions. For PM2.5, the coarse run cannot selectively incorporate local scale features in order to reduce model error. Hide

Molecular organic tracer compounds were analyzed in six particle sizes in an urban background site (Barcelona) and in a rural site in Spain. The results improve considerably our current understanding on the composition and particle-size distribution of organic air pollution in traffic intensive urban areas and rural sites where combustion of biomass plays an important role on the local and regional air quality, either by emissions from open fires or from domestic heating. Hide