R. Makkonen

Production of extremely low volatile organic compounds from biogenic emissions: Measured yields and atmospheric implications

Significance Extremely low volatility organic compounds (ELVOC) are suggested to promote aerosol particle formation and cloud condensation nuclei (CCN) production in the atmosphere. We show that the capability of biogenic VOC (BVOC) to produce ELVOC depends strongly on their chemical structure and relative oxidant levels. BVOC with an endocyclic double bond, representative emissions from, e.g., boreal forests, efficiently produce ELVOC from ozonolysis. Compounds with exocyclic double bonds or acyclic compounds including isoprene, emission representative of the tropics, produce minor quantities of ELVOC, and the role of OH radical oxidation is relatively larger. Implementing these findings into a global modeling framework shows that detailed assessment of ELVOC production pathways is crucial for understanding biogenic secondary organic aerosol and atmospheric CCN formation. Oxidation products of monoterpenes and isoprene have a major influence on the global secondary organic aerosol (SOA) burden and the production of atmospheric nanoparticles and cloud condensation nuclei (CCN). Here, we investigate the formation of extremely low volatility organic compounds (ELVOC) from O3 and OH radical oxidation of several monoterpenes and isoprene in a series of laboratory experiments. We show that ELVOC from all precursors are formed within the first minute after the initial attack of an oxidant. We demonstrate that under atmospherically relevant concentrations, species with an endocyclic double bond efficiently produce ELVOC from ozonolysis, whereas the yields from OH radical-initiated reactions are smaller. If the double bond is exocyclic or the compound itself is acyclic, ozonolysis produces less ELVOC and the role of the OH radical-initiated ELVOC formation is increased. Isoprene oxidation produces marginal quantities of ELVOC regardless of the oxidant. Implementing our laboratory findings into a global modeling framework shows that biogenic SOA formation in general, and ELVOC in particular, play crucial roles in atmospheric CCN production. Monoterpene oxidation products enhance atmospheric new particle formation and growth in most continental regions, thereby increasing CCN concentrations, especially at high values of cloud supersaturation. Isoprene-derived SOA tends to suppress atmospheric new particle formation, yet it assists the growth of sub-CCN-size primary particles to CCN. Taking into account compound specific monoterpene emissions has a moderate effect on the modeled global CCN budget.

Climate Feedbacks Linking the Increasing Atmospheric CO2 Concentration, BVOC Emissions, Aerosols and Clouds in Forest Ecosystems

Biogenic volatile organic compounds (BVOCs) play a central role in atmospheric chemistry via their high reactivity in the gas phase and via their participation in atmospheric new particle formation and secondary organic aerosol formation. The emissions of BVOC to the atmosphere depend on several climate-related variables, making these compounds part of complex, yet potentially very important, climate feedback mechanisms. Here we illustrated the role of BVOCs in enhancing gross primary production (GPP) and cloud droplet number concentrations. The first of these phenomena forms a positive feedback loop for the terrestrial carbon sink (GPP feedback), whereas the second one forms a negative feedback loop for the ambient temperature increase (temperature feedback).

A production-tagged aerosol module for Earth system models, OsloAero5.3 – extensions and updates for CAM5.3-Oslo

The article untitled “A production-tagged aerosol module for earth system models, OsloAero5.3 – extensions and updates for CAM5.3-Oslo” by A. Kirkevag et al. presents in a very detailed way updates in the modelisation of aerosols that is used in the atmospheric component of the Norwegian Earth System Model (NorESM). This updated version called OsloAero5.3 is here tested in the CAMS5.3 atmospheric model which is part of the Community Earth System Model 1.2 (CESM). With regards to the CMIP6 project, OsloAero5.3 is planned to be integrated/merged with CEMS2 to form the NorESM2 model, but the version presented in this article could be used for the early phase of CMIP6. Therefore, in addition to being of value to the aerosol modelling community, the discussions in the article are fully relevant to the CMIP6 exercise.

New Parameterizations for Neutral and Ion-Induced Sulfuric Acid-Water Particle Formation in Nucleation and Kinetic Regimes

We have developed new parameterizations of electrically neutral homogeneous and ion-induced sulfuric acid - water particle formation for large ranges of environmental conditions, based on an improved model that has been validated against a particle formation rate data set produced by Cosmics Leaving OUtdoor Droplets (CLOUD) experiments at CERN. The model uses a thermodynamically consistent version of the Classical Nucleation Theory normalized using quantum chemical data. Unlike the earlier parameterizations for H 2 SO 4 -H 2 O nucleation, the model is applicable to extreme dry conditions where the one-component sulfuric acid limit is approached. Parameterizations are presented for the critical cluster sulfuric acid mole fraction, the critical cluster radius, the total number of molecules in the critical cluster, and the particle formation rate. If the critical cluster contains only one sulfuric acid molecule, a simple formula for kinetic particle formation can be used: this threshold has also been parameterized. The parameterization for electrically neutral particle formation is valid for the following ranges: temperatures 165-400 K, sulfuric acid concentrations 10 4 -10 13 cm −3 and relative humidities 0.001-100%. The ion-induced particle formation parameterization is valid for temperatures 195-400 K, sulfuric acid concentrations 10 4 -10 16 cm −3 and relative humidities 10 −5 -100%. The new parameterizations are thus applicable for the full range of conditions in the Earths atmosphere relevant for binary sulfuric acid - water particle formation, including both tropospheric and stratospheric conditions. They are also suitable for describing particle formation in the atmosphere of Venus.

PAN-EURASIAN EXPERIMENT (PEEX) PROGRAM: AN OVERVIEW OF THE FIRST 5 YEARS IN OPERATION AND FUTURE PROSPECTS

The Pan-Eurasian Experiment (PEEX) program was initiated as a bottom-up approach by the researchers coming fromFinlandandRussiain October 2012. The PEEX China kick off meeting was held in November 2013. During its five years in operation, the program has established a governance structure and delivered a science plan for the Northern Eurasian region. PEEX has also introduced a concept design for a modelling platform and ground-based in situ observation systems for detecting land-atmosphere and ocean-atmosphere interactions. Today, PEEX has an extensive researcher’s network representing research communities coming from the Nordic countries,RussiaandChina. PEEX is currently carrying out its research activities on a project basis, but is looking for more coordinated funding bases, especially inRussiaand inChina. The near-future challenge in implementing the PEEX research agenda is to achieve a successful integration and identification of the methodological approaches of the socio-economic research to environmental sciences. Here we give insight into these issues and provide an overview on the main tasks for the upcoming years.

Anthropogenic aerosol forcing n insights from multi-estimates from aerosol-climate models with reduced complexity

The radiative forcing of anthropogenic aerosol remains a key uncertainty in the understanding of climate change. This study quantifies the model spread in aerosol forcing associated with (i) variability internal to the atmosphere and (ii) differences in the model representation of weather. We do so by performing ensembles of atmosphere-only simulations with four state-of-the-art Earth system models, three of which will be used in the sixth coupled model inter-comparison project (CMIP6, Eyring et al., 2016). In those models we reduce the complexity of the anthropogenic aerosol by prescribing the same 5 annually-repeating patterns of the anthropogenic aerosol optical properties and associated effects on the cloud reflectivity. We quantify a comparably small model spread in the long-term averaged ERF compared to the overall possible range in annual ERF estimates associated with model-internal variability. This implies that identifying the true model spread in ERF associated with differences in the representation of meteorological processes and natural aerosol requires averaging over a sufficiently large number of annual estimates. We characterize the model diversity in clouds and use satellite products as benchmarks. 10 Despite major inter-model differences in natural aerosol and clouds, all models show only a small change in the global-mean ERF due to the substantial change in the global anthropogenic aerosol distribution between the mid-1970s and mid-2000s, the ensemble mean ERF being -0.47 Wm−2 for the mid-1970s and -0.51 Wm−2 for the mid-2000s. This result suggests that inter-comparing ERF changes between two periods rather than absolute magnitudes relative to pre-industrial might provide a more stringent test for a model’s ability for representing climate evolutions. 15

Climatic implications of the Brazilian biofuel transition

A global climate model is being run to study the consequences of Brazil transitioning from fossil to biofuels over the next few decades. Assuming all other factors constant, preliminary results suggest little to no climatic relevance.

Effect of Nucleation and Secondary Organic Aerosol Formation on Cloud Droplet Number Concentrations

The global general circulation model ECHAM5 is used together with HAM aerosol module to investigate the effect of the nucleation scheme on cloud droplet number concentrations. It is shown that nucleation can have a significant role on indirect aerosol effect. Also an efficient SOA formation scheme is intro- duced, and results are compared with original ECHAM5-HAM.