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Rapid warming is likely increasing primary production and wildfire occurrence in the Arctic. Projected changes in the abundance and composition of carbonaceous aerosols during the summer are likely to impact atmospheric chemistry and climate, but our understanding of these processes is limited by sparse observations. Here, we characterize carbonaceous aerosol at two field sites, Toolik Field Station in the Interior and the Atmospheric Radiation Measurement facility at Utqiaġvik on the Arctic coast of Alaska, USA, through the summers of 2022 and 2023. We estimated particulate matter ≤2.5 micrometers (PM2.5) and particulate matter ≤10 micrometers (PM10) using laser light scattering (PurpleAir sensors) and examined total carbon (TC) and its organic carbon (OC) and elemental carbon (EC) fractions in total suspended particles (TSP). We also investigated the dominant sources of carbonaceous aerosol using air mass backward-trajectories from the National Oceanic and Atmospheric Administration (NOAA) Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and radiocarbon source apportionment of TC. We found TC concentrations were about twice as high in the Interior than on the coast and that modern sources were the dominant sources of carbonaceous aerosol at both Toolik (95–99%) and Utqiaġvik (86–89%), with minor contributions from fossil sources. Periods of significantly elevated PM, TC, OC, and EC concentrations coincided with major boreal forest fire activity in North America that brought smoke to the region. The radiocarbon signature of EC measured at Toolik during these wildfire smoke events indicated that over 90% of the EC originated from modern sources. Our measurements demonstrate changing aerosol concentrations in the Arctic during the summer, and emphasize the need for continuous atmospheric monitoring to evaluate and advance our understanding of this rapidly changing atmospheric environment. (Manuscript in prep) 

Abstract. We present the Fire Inventory from National Center for Atmospheric Research (NCAR) version 2.5 (FINNv2.5), a fire emissions inventory that provides publicly available emissions of trace gases and aerosols for various applications, including use in global and regional atmospheric chemistry modeling. FINNv2.5 includes numerous updates to the FINN version 1 framework to better represent burned area, vegetation burned, and chemicals emitted. Major changes include the use of active fire detections from the Visible Infrared Imaging Radiometer Suite (VIIRS) at 375 m spatial resolution, which allows smaller fires to be included in the emissions processing. The calculation of burned area has been updated such that a more rigorous approach is used to aggregate fire detections, which better accounts for larger fires and enables using multiple satellite products simultaneously for emissions estimates. Fuel characterization and emissions factors have also been updated in FINNv2.5. Daily fire emissions for many trace gases and aerosols are determined for 2002–2019 (Moderate Resolution Imaging Spectroradiometer (MODIS)-only fire detections) and 2012–2019 (MODIS + VIIRS fire detections). The non-methane organic gas emissions are allocated to the species of several commonly used chemical mechanisms. We compare FINNv2.5 emissions against other widely used fire emissions inventories. The performance of FINNv2.5 emissions as inputs to a chemical transport model is assessed with satellite observations. Uncertainties in the emissions estimates remain, particularly in Africa and South America during August–October and in southeast and equatorial Asia in March and April. Recommendations for future evaluation and use are given.

 

Abstract. While camphene is one of the dominant monoterpenesmeasured in biogenic and pyrogenic emission samples, oxidation of camphenehas not been well-studied in environmental chambers and very little is knownabout its potential to form secondary organic aerosol (SOA). The lack ofchamber-derived SOA data for camphene may lead to significant uncertaintiesin predictions of SOA from oxidation of monoterpenes using existingparameterizations when camphene is a significant contributor to totalmonoterpenes. Therefore, to advance the understanding of camphene oxidationand SOA formation and to improve representation of camphene in air qualitymodels, a series of experiments was performed in the University ofCalifornia Riverside environmental chamber to explore camphene SOA massyields and properties across a range of chemical conditions atatmospherically relevant OH concentrations. The experimental results werecompared with modeling simulations obtained using two chemically detailedbox models: Statewide Air Pollution Research Center (SAPRC) and Generatorfor Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A).SOA parameterizations were derived from the chamber data using both thetwo-product and volatility basis set (VBS) approaches. Experiments performedwith added nitrogen oxides (NOx) resulted in higher SOA mass yields (upto 64 %) than experiments performed without added NOx (up to 28 %).In addition, camphene SOA mass yields increased with SOA mass (Mo) atlower mass loadings, but a threshold was reached at higher mass loadings inwhich the SOA mass yields no longer increased with Mo. SAPRC modelingof the chamber studies suggested that the higher SOA mass yields at higherinitial NOx levels were primarily due to higher production of peroxyradicals (RO2) and the generation of highly oxygenated organicmolecules (HOMs) formed through unimolecular RO2 reactions. SAPRCpredicted that in the presence of NOx, camphene RO2 reacts with NOand the resultant RO2 undergoes hydrogen (H)-shift isomerizationreactions; as has been documented previously, such reactions rapidly addoxygen and lead to products with very low volatility (i.e., HOMs). The endproducts formed in the presence of NOx have significantly lowervolatilities, and higher O : C ratios, than those formed by initial campheneRO2 reacting with hydroperoxyl radicals (HO2) or other RO2.Further analysis reveals the existence of an extreme NOx regime, whereinthe SOA mass yield can be suppressed again due to high NO / HO2 ratios.Moreover, particle densities were found to decrease from 1.47 to 1.30 g cm−3 as [HC]0 / [NOx]0 increased and O : C decreased. Theobserved differences in SOA mass yields were largely explained by thegas-phase RO2 chemistry and the competition between RO2+HO2, RO2+ NO, RO2+ RO2, and RO2 autoxidationreactions. 

Warming climate in the Arctic is leading to an increase in isoprene emission from ecosystems. We assessed the influence of temperature on isoprene emission from Arctic willows with laboratory and field measurements. Our findings indicate that the hourly temperature response curve ofSalixspp., the dominant isoprene emitting shrub in the Arctic, aligns with that of temperate plants. In contrast, the isoprene capacity of willows exhibited a more substantial than expected response to the mean ambient temperature of the previous day, which is much stronger than the daily temperature response predicted by the current version of the Model of Emissions of Gases and Aerosols from Nature (MEGAN). With a modified algorithm from this study, MEGAN predicts 66% higher isoprene emissions for Arctic willows during an Arctic heatwave. However, despite these findings, we are still unable to fully explain the high temperature sensitivity of isoprene emissions from high latitude ecosystems.

 

The basicity constant, or p K b , is an intrinsic physical property of bases that gives a measure of its proton affinity in macroscopic environments. While the p K b is typically defined in reference to the bulk aqueous phase, several studies have suggested that this value can differ significantly at the air–water interface (which can have significant ramifications for particle surface chemistry and aerosol growth modeling). To provide mechanistic insight into surface proton affinity, we carried out ab initio metadynamics calculations to (1) explore the free-energy profile of dimethylamine and (2) provide reasonable estimates of the p K b value in different solvent environments. We find that the free-energy profiles obtained with our metadynamics calculations show a dramatic variation, with interfacial aqueous dimethylamine p K b values being significantly lower than in the bulk aqueous environment. Furthermore, our metadynamics calculations indicate that these variations are due to reduced hydrogen bonding at the air–water surface. Taken together, our quantum mechanical metadynamics calculations show that the reactivity of dimethylamine is surprisingly complex, leading to p K b variations that critically depend on the different atomic interactions occurring at the microscopic molecular level.