Measurements of the radioactive carbon isotope ¹⁴C allow to identify the sources of aerosol carbon. We report an extensive ¹⁴C source apportionment record in the Netherlands with samples covering a whole year. We discovered that long-range transport has a large influence on aerosol carbon levels. Fossil fuel carbon is least influenced by long-range transport and more regional in origin. Biomass burning seems to be a minor source of aerosol carbon in the Netherlands. Hide

Using different meteorology reanalyses to drive dust in climate modeling can produce dissimilar global dust distributions, especially in the Southern Hemisphere (SH). It may therefore not be advisable for SH dust studies to base results on simulations driven by one reanalysis. Northern Hemisphere dust varies mostly on seasonal timescales, while SH dust varies on interannual timescales. Dust is an important part of climate modeling, and we hope this contributes to understanding these simulations. Hide

We quantify the relative contribution of processes controlling the interannual variability (IAV) of tropospheric ozone over the southern hemispheric tropospheric ozone maximum (SHTOM) with GMI chemistry transport model. We use various GMI tracer diagnostics, including a StratO₃ tracer to quantify the stratospheric impact, and tagged CO tracers to track the emission sources. Our result shows that the stratospheric contribution is the most important factor driving the IAV of upper tropospheric O₃. Hide

A method has been introduced to assess the representativeness of the time series of a point measurement compared to results for a larger area centered around the measurement location. This method allows one to determine the optimal accuracy that can be achieved for the validation of satellite products for a given pixel footprint, or the evaluation of an atmospheric model with a given grid-cell resolution. Hide

This study analyses shortwave radiation (SW) in the G4 experiment of the Geoengineering Model Intercomparison Project. G4 involves stratospheric injection of 5 Tg yr⁻¹ of SO₂ against the RCP4.5 scenario. The global mean forcing of the sulphate geoengineering has an inter-model variablity of −3.6 to −1.6 W m⁻², implying a high uncertainty in modelled processes of sulfate aerosols. Changes in water vapour and cloud amounts due to the SO₂ injection weaken the forcing at the surface by around 50 %. Hide

We present spring and summer VOC emission rate measurements from Norway spruce using an in situ gas chromatograph. Monoterpene and C₄–C₁₀ aldehyde emission rates reached maxima in July. SQT emissions increased at the end of July and in August SQT were the most abundant group. The MT emission pattern varied a lot from tree to tree and therefore emission fluxes on canopy level should be conducted for more representative measurements. However, leaf level measurements produce more reliable SQT data. Hide

A convection-permitting limited area model with prognostic aerosol microphysics is applied to investigate how concentrations of cloud condensation nuclei (CCN) in the marine boundary layer are affected by high-resolution dynamical and thermodynamic fields at sub-climate model scale. We gain new insight into the way primary sea-salt and secondary sulfate particles contribute to the overall CCN variance, and find a marked difference in the variability of super- and sub-micron CCN. Hide

The Yangtze River Delta is one of the most industrialized regions in China. In situ optical isotopic measurement in Nanjing, a city located in the Delta, showed unusually high atmospheric δ¹³C signals in the summer (−7.44 ‰, July 2013 mean), which we attributed to the influence of cement production in the region. Flux partitioning calculations revealed that natural ecosystems in the region were a negligibly small source of atmospheric CO₂. Hide

The generally accepted mechanism leading to ozone depletion events in the Arctic assumes efficient gas-phase recycling of bromine atoms, such that the rate of ozone depletion has often been estimated as the rate that Br atoms regenerate through gas-phase BrO + BrO and BrO + ClO reactions. Using a large suite of data from the OASIS2009 campaign, our modeling results show that the gas-phase regeneration of Br is less efficient than expected and that heterogeneous recycling on surfaces is critical. Hide

This paper reports a systematic assessment of the information content of remote sensing measurements with regard to the chemical composition of aerosols. The focus is on ground-based, airborne, or space-borne lidar observations. The results are exploited in an air-quality forecasting model by incorporating measurements into the model in such a way that one maximises the use of available information. The goal of this work is to improve air-quality forecasting for suspended particulate matter. Hide

Observation and simulation show an Atlantic ozone streamer along the edge region of the polar vortex in the northern middle stratosphere during winter. The Atlantic streamer has wind speeds of about 100 m/s and turns equatorward at a vortex erosion region. We compare the fields of stratospheric ozone and water vapour from ground- and space-based microwave radiometry and SD-WACCM simulations for a better understanding of non-linear transport processes in the middle atmosphere. Hide

Toluene, one of the principle aromatic compounds present in the atmosphere, is oxidized by OH to produce cresol and other products. Here later-generation low-volatility oxygenated products from cresol oxidation by OH are detected in the gas and particle phases. This work identifies a simple and significant mechanism for toluene secondary organic aerosol formation through the cresol pathway. Likely the phenolic pathway of other aromatic compounds is also important for secondary organic aerosol. Hide

Estimating impacts of wood combustion on ambient levels of PAHs is challenging. In this study effect of residential wood combustion on the benzo[a]pyrene concentrations in the air of Helsinki metropolitan area was studied, using ambient air measurements, emission estimates and dispersion modeling. Combining all this information enabled a quantitative characterization of the influence of residential wood combustion, which was found to be the main local source and more important than for PM_2.5. Hide

A record of light-absorbing refractory black carbon (rBC), emitted by fossil fuel combustion and biomass burning, was reconstructed from the ice cores drilled at a high-altitude eastern European site in Mt. Elbrus. This record reports for the first time the high-resolution rBC mass concentrations in the European outflows over the past 189 years. Our study suggests that the past changes in BC emissions of eastern Europe need to be considered in assessing ongoing air quality regulations. Hide

Tropical cyclones are significantly influenced by the lowest part of atmosphere from sea surface to 1 km because strong winds interacting with ocean surface may provide significant energy to the storms. This work aims to understand how different wind intensity and shape may change the energy transfer. A numerical modeling technique is used to simulate the wind and energy transfer. It is found that the change in wind speed with height is particularly important in generating energy transport. Hide

To improve the understanding of heterogeneous ice nucleation, we have subjected different ice nuclei to repeated freezing cycles and evaluated the freezing temperatures with different parameterizations of classical nucleation theory. It was found that two fit parameters were necessary to describe the temperature dependence of the nucleation rate. Hide

Methane (CH₄) fluxes were estimated for the high northern latitudes for 2005–2013 based on observations of atmospheric CH₄ mixing ratios. Methane fluxes were found to be higher than prior estimates in northern Eurasia and Canada, especially in the Western Siberian Lowlands and the Canadian province Alberta. Significant inter-annual variations in the fluxes were found as well as a small positive trend. In Canada, the trend may be related to an increase in soil temperature over the study period. Hide

Simulations from eight atmospheric models have been compared to tracer and temperature observations from seven satellite instruments in order to evaluate the energetic particle indirect effect (EPP IE) during the perturbed northern hemispheric (NH) winter 2008/2009. Models are capable to reproduce the EPP IE in dynamically and geomagnetically quiescent NH winter conditions. The results emphasize the need for model improvements in the dynamical representation of elevated stratopause events. Hide

This paper presents data on the size, composition and concentration of aerosol particles emitted from north Australian savannah fires and how these properties influence cloud condensation nuclei (CCN) concentrations. Both the size and composition of aerosol were found to be important in determining CCN. Despite large CCNc enhancements during periods of close biomass burning, the aerosol was very weakly hygroscopic which should be accounted for in climate models to avoid large CCNc overestimates. Hide

We derive the first comprehensive statistics of cirrus clouds over a tropical rain forest. Monthly frequency of occurrence can be as high as 88 %. The diurnal cycle follows that of precipitation, and frequently cirrus is found in the tropopause layer. The mean values of cloud top, base, thickness, optical depth and lidar ratio were 14.3 km, 12.9 km, 1.4 km, 0.25, and 23 sr respectively. The high fraction (42 %) of subvisible clouds may contaminate satellite measurements to an unknown extent. Hide

We quantify the importance in the atmosphere of different aerosol components to contribute to global ice-nucleating particles concentrations (INPs). The aim is to improve the way atmospheric cloud-ice processes are represented in climate models so they will be able to make better predictions in the future. We found that a kind of dust (K-feldspar), together with marine organic aerosols, can help to improve the representation of INPs and explain most of their observations. Hide

HULIS are demonstrated to be important low-volatility, or even extremely low volatility, compounds in the organic aerosol phase. This sheds new light on the connection between atmospheric HULIS and ELVOCs. The interaction between HULIS and ammonium sulfate was found to decrease the volatility of the HULIS part in HULIS-AS mixed samples, indicating multiphase processes have the potential to lower the volatility of organic compounds in the aerosol phase. Hide

This study examined the contribution of two natural sources (long-range transport of African dust and sea salt) to the airborne particulate matter concentrations, in 5 southern European cities (Porto, Barcelona, Milan, Florence, Athens). The results demonstrated that natural sources are often expressed with high-intensity events, leading even to exceedances of the EU air quality standards. This effect was more pronounced in the case of African dust intrusions in the eastern Mediterranean area. Hide

Radiative forcing by aerosol–cloud interactions (RF_aci) remains highly uncertain and difficult to quantify on the basis of current knowledge. The present study reassesses the estimated RF_aci by using a new statistical fitting approach, which improves the quantification of RF_aci with less uncertainty. The present work helps to improve the parameterisation of RF_aci in the present climate model. Hide

The emissions and distribution of wintertime sea salt aerosol (SSA) are poorly constrained in polar regions, despite their potentially significant roles in halogen release, cloud formation and climate. We implement a blowing snow and a frost flower emission scheme in the model, and find that inclusion of blowing snow is necessary to simulate the observed winter and spring SSA levels. We estimate that inclusion of blowing snow increases submicron SSA emissions by factors of 2–3 in polar regions. Hide

We show the first simultaneous observations of triple oxygen isotopic compositions of atmospheric sulfate, nitrate, and ozone at Dumont d'Urville, coastal Antarctica. The contrasting seasonal trends between oxygen isotopes of ozone and those of sulfate and nitrate indicate that these signatures in sulfate and nitrate are mainly controlled by changes in oxidation chemistry. We also discuss the specific oxidation chemistry induced by the unique phenomena at the site. Hide

Asian O₃ outflow exhibited a small and statistically insignificant decadal trend with large interannual variations from 1986–2006. The latter were mainly caused by variations in the meteorological conditions. Future climate change will aggravate the effects of the increases in anthropogenic emissions on future changes in the Asian O₃ outflow. These findings help us to understand the variations in tropospheric O₃ in the regions downwind of East Asia on different timescales. Hide

Dry deposition of tropospheric ozone relates to its destruction at the Earth’s surface. An improved model scheme for such deposition to the ocean is formulated backed up by field data. It results in the oceanic dry deposition of ozone to be 12 % of the global total, which is much lower than the current model estimate of about 30 %. This result has implications for modelling global tropospheric ozone budget and its radiative forcing, and ozone mixing ratios, especially in the Southern Hemisphere. Hide

To better understand the sources of uncertainty in modeled Arctic tropospheric oxidants, we created and analyzed an ensemble of chemical transport model runs with inputs perturbed according to their respective uncertainties. Ozone and OH were most sensitive to various emissions and chemical factors. HO₂ was overwhelmingly sensitive to aerosol particle uptake. When compared to airborne measurements, better agreement was found when the model used lower aerosol particle uptake rates. Hide