Terpenylic Acid and Related Compounds from the Oxidation of α-Pinene: Implications for New Particle Formation and Growth above Forests

Novel secondary organic aerosol (SOA) products from the monoterpene α-pinene with unique dimer-forming properties have been identified as lactone-containing terpenoic acids, i.e., terpenylic and 2-hydroxyterpenylic acid, and diaterpenylic acid acetate. The structural characterizations were based on the synthesis of reference compounds and detailed interpretation of mass spectral data. Terpenylic acid and diaterpenylic acid acetate are early oxidation products generated upon both photooxidation and ozonolysis, while 2-hydroxyterpenylic acid is an abundant SOA tracer in ambient fine aerosol that can be explained by further oxidation of terpenylic acid. Quantum chemical calculations support that noncovalent dimer formation involving double hydrogen bonding interactions between carboxyl groups of the monomers is energetically favorable. The molecular properties allow us to explain initial particle formation in laboratory chamber experiments and are suggested to play a role in new particle formation and growth above forests, a natural phenomenon that has fascinated scientists for more than a century

Experimental study of the role of physicochemical surface processing on the IN ability of mineral dust particles

During the measurement campaign FROST 2 (FReezing Of duST 2), the Leipzig Aerosol Cloud Interaction Simulator (LACIS) was used to investigate the influence of various surface modifications on the ice nucleating ability of Arizona Test Dust (ATD) particles in the immersion freezing mode. The dust particles were exposed to sulfuric acid vapor, to water vapor with and without the addition of ammonia gas, and heat using a thermodenuder operating at 250 °C. Size selected, quasi monodisperse particles with a mobility diameter of 300 nm were fed into LACIS and droplets grew on these particles such that each droplet contained a single particle. Temperature dependent frozen fractions of these droplets were determined in a temperature range between −40 °C ≤T≤−28 °C. The pure ATD particles nucleated ice over a broad temperature range with their freezing behavior being separated into two freezing branches characterized through different slopes in the frozen fraction vs. temperature curves. Coating the ATD particles with sulfuric acid resulted in the particles' IN potential significantly decreasing in the first freezing branch (T>−35 °C) and a slight increase in the second branch (T≤−35 °C). The addition of water vapor after the sulfuric acid coating caused the disappearance of the first freezing branch and a strong reduction of the IN ability in the second freezing branch. The presence of ammonia gas during water vapor exposure had a negligible effect on the particles' IN ability compared to the effect of water vapor. Heating in the thermodenuder led to a decreased IN ability of the sulfuric acid coated particles for both branches but the additional heat did not or only slightly change the IN ability of the pure ATD and the water vapor exposed sulfuric acid coated particles. In other words, the combination of both sulfuric acid and water vapor being present is a main cause for the ice active surface features of the ATD particles being destroyed. A possible explanation could be the chemical transformation of ice active metal silicates to metal sulfates. The strongly enhanced reaction between sulfuric acid and dust in the presence of water vapor and the resulting significant reductions in IN potential are of importance for atmospheric ice cloud formation. Our findings suggest that the IN concentration can decrease by up to one order of magnitude for the conditions investigated

Ice-nucleating particle versus ice crystal number concentrationin altocumulus and cirrus layers embedded in Saharan dust:a closure study

For the first time, a closure study of the relationship between the ice-nucleating particle concentration (INP; INPC) and ice crystal number concentration (ICNC) in altocumulus and cirrus layers, solely based on groundbased active remote sensing, is presented. Such aerosol- cloud closure experiments are required (a) to better understand aerosol-cloud interaction in the case of mixed-phase clouds, (b) to explore to what extent heterogeneous ice nucleation can contribute to cirrus formation, which is usually controlled by homogeneous freezing, and (c) to check the usefulness of available INPC parameterization schemes, applied to lidar profiles of aerosol optical and microphysical properties up to the tropopause level. The INPC-ICNC closure studies were conducted in Cyprus (Limassol and Nicosia) during a 6-week field campaign in March-April 2015 and during the 17-month CyCARE (Cyprus Clouds Aerosol and Rain Experiment) campaign. The focus was on altocumulus and cirrus layers which developed in pronounced Saharan dust layers at heights from 5 to 11 km. As a highlight, a long-lasting cirrus event was studied which was linked to the development of a very strong dust-infused baroclinic storm (DIBS) over Algeria. The DIBS was associated with strong convective cloud development and lifted large amounts of Saharan dust into the upper troposphere, where the dust influenced the evolution of an unusually large anvil cirrus shield and the subsequent transformation into an cirrus uncinus cloud system extending from the eastern Mediterranean to central Asia, and thus over more than 3500 km. Cloud top temperatures of the three discussed closure study cases ranged from - 20 to -57 °C. The INPC was estimated from polarization/Raman lidar observations in combination with published INPC parameterization schemes, whereas the ICNC was retrieved from combined Doppler lidar, aerosol lidar, and cloud radar observations of the terminal velocity of falling ice crystals, radar reflectivity, and lidar backscatter in combination with the modeling of backscattering at the 532 and 8.5 mm wavelengths. A good-to-acceptable agreement between INPC (observed before and after the occurrence of the cloud layer under investigation) and ICNC values was found in the discussed three proof-of-concept closure experiments. In these case studies, INPC and ICNC values matched within an order of magnitude (i.e., within the uncertainty ranges of the INPC and ICNC estimates), and they ranged from 0.1 to 10 L-1 in the altocumulus layers and 1 to 50 L-1 in the cirrus layers observed between 8 and 11 km height. The successful closure experiments corroborate the important role of heterogeneous ice nucleation in atmospheric ice formation processes when mineral dust is present. The observed longlasting cirrus event could be fully explained by the presence of dust, i.e., without the need for homogeneous ice nucleation processes

Corrigendum to "Experimental study of the role of physicochemical surface processing on the IN ability of mineral dust particles" published in Atmos. Chem. Phys., 11, 11131–11144, 2011

In the abstract of the manuscript, the following sentence needs to be corrected: “A possible explanation could be the chemical transformation of ice active metal silicates to metal sulfates.” “metal silicates” is wrong. It should be “aluminosilicates”

Particulate emissions from commercial shipping: chemical, physical, and optical properties

, 39% OM, and 15% BC and differs from inventories that used 81%, 14%, and 5% and 31%, 63%, and 6% SO 4 2À , OM, and BC, respectively. SO 4 2À and OM mass were found to be dependent on fuel sulfur content as were SSA, hygroscopicity, and CCN concentrations. BC mass was dependent on engine type and combustion efficiency. A plume evolution study conducted on one vessel showed conservation of particle light absorption, decrease in CN > 5 nm, increase in particle hygroscopicity, and an increase in average particle size with distance from emission. These results suggest emission of small nucleation mode particles that subsequently coagulate/condense onto larger BC and OM. This work contributes to an improved understanding of the impacts of ship emissions on climate and air quality and will also assist in determining potential effects of altering fuel standards

Black carbon surface oxidation and organic composition of beech-wood soot aerosols

Soot particles are the most strongly light-absorbing particles commonly found in the atmosphere. They are major contributors to the radiative budget of the Earth and to the toxicity of atmospheric pollution. Atmospheric aging of soot may change its health- and climate-relevant properties by oxidizing the primary black carbon (BC) or organic particulate matter (OM) which, together with ash, comprise soot. This atmospheric aging, which entails the condensation of secondary particulate matter as well as the oxidation of the primary OM and BC emissions, is currently poorly understood. In this study, atmospheric aging of wood-stove soot aerosols was simulated in a continuous-flow reactor. The composition of fresh and aged soot particles was measured in real time by a dual-vaporizer aerosol-particle mass spectrometer (SP-AMS). The dual-vaporizer SP-AMS provided information on the OM and BC components of the soot as well as on refractory components internally mixed with BC. By switching the SP-AMS laser vaporizer off and using only the AMS thermal vaporizer (at 600 °C), information on the OM component only was obtained. In both modes, OM appeared to be generated largely by cellulose and/or hemicellulose pyrolysis and was only present in large amounts when new wood was added to the stove. In SP-AMS mode, BC signals otherwise dominated the mass spectrum. These signals consisted of ions related to refractory BC (rBC, C1-5+), oxygenated carbonaceous ions (CO1-2+), potassium (K+), and water (H2O+ and related fragments). The C4+ : C3+ ratio, but not the C1+ : C3+ ratio, was consistent with the BC-structure trends of Corbin et al. (2015c). The CO1-2+ signals likely originated from BC surface groups: upon aging, both CO+ and CO2+ increased relative to C1-3+ while CO2+ simultaneously increased relative to CO+. Factor analysis (positive matrix factorization) of SP-AMS and AMS data, using a modified error model to address peak-integration uncertainties, indicated that the surface composition of the BC was approximately constant across all stages of combustion for both fresh and aged samples. These results represent the first time-resolved measurements of in situ BC surface aging and suggest that the surface of beech-wood BC may be modelled as a single chemical species.ISSN:1680-7375ISSN:1680-736

Heterogeneous ice nucleation on dust particles sourced from nine deserts worldwide - Part 2: Deposition nucleation and condensation freezing

Mineral dust particles from deserts are amongst the most common ice nucleating particles in the atmosphere. The mineralogy of desert dust differs depending on the source region and can further fractionate during the dust emission processes. Mineralogy to a large extent explains the ice nucleation behavior of desert aerosol, but not entirely. Apart from pure mineral dust, desert aerosol particles often exhibit a coating or are mixed with small amounts of biological material. Aging on the ground or during atmospheric transport can deactivate nucleation sites, thus strong ice nucleating minerals may not exhibit their full potential. In the partner paper of this work, it was shown that mineralogy determines most but not all of the ice nucleation behavior in the immersion mode found for desert dust. In this study, the influence of semi-volatile organic compounds and the presence of crystal water on the ice nucleation behavior of desert aerosol is investigated. This work focuses on the deposition and condensation ice nucleation modes at temperatures between 238 and 242 K of 18 dust samples sourced from nine deserts worldwide. Chemical imaging of the particles' surface is used to determine the cause of the observed differences in ice nucleation. It is found that, while the ice nucleation ability of the majority of the dust samples is dominated by their quartz and feldspar content, in one carbonaceous sample it is mostly caused by organic matter, potentially cellulose and/or proteins. In contrast, the ice nucleation ability of an airborne Saharan sample is found to be diminished, likely by semi-volatile species covering ice nucleation active sites of the minerals. This study shows that in addition to mineralogy, other factors such as organics and crystal water content can alter the ice nucleation behavior of desert aerosol during atmospheric transport in various ways.ISSN:1680-7375ISSN:1680-736

Technical Note: The single particle soot photometer failsto reliably detect PALAS soot nanoparticles

The single particle soot photometer (SP2) useslaser-induced incandescence (LII) for the measurement of at-mospheric black carbon (BC) particles. The BC mass con-centration is obtained by combining quantitative detectionof BC mass in single particles with a counting efficiency of100 % above its lower detection limit. It is commonly ac-cepted that a particle must contain at least several tenths ofa femtogram BC in order to be detected by the SP2.Here we show the result that most BC particles froma PALAS spark discharge soot generator remain undetectedby the SP2, even if their BC mass, as independently de-termined with an aerosol particle mass analyser (APM),is clearly above the typical lower detection limit of theSP2. Comparison of counting efficiency and effective densitydata of PALAS soot with flame generated soot (combustionaerosol standard burner, CAST), fullerene soot and carbonblack particles (Cabot Regal 400R) reveals that particle mor-phology can affect the SP2’s lower detection limit. PALASsoot particles are fractal-like agglomerates of very small pri-mary particles with a low fractal dimension, resulting in avery low effective density. Such loosely packed particles be-have like “the sum of individual primary particles” in theSP2’s laser. Accordingly, most PALAS soot particles remainundetected as the SP2’s laser intensity is insufficient to heatthe primary particles to their vaporisation temperature be-cause of their small size (Dpp≈5–10 nm). Previous knowl-edge from pulsed laser-induced incandescence indicated thatparticle morphology might have an effect on the SP2’s lowerdetection limit, however, an increase of the lower detection limit by a factor of∼5–10, as reported here for PALAS soot,was not expected.In conclusion, the SP2’s lower detection limit at a cer-tain laser power depends primarily on the total BC massper particle for compact particles with sufficiently high ef-fective density. By contrast, the BC mass per primary par-ticle mainly determines whether fractal-like particles withlow fractal dimension and very small primary particles aredetectable, while their total BC mass has only a minor in-fluence. This effect shifts the lower detection limit to muchhigher BC mass, or makes them completely undetectable.Consequently, care has to be taken when using the SP2 inapplications dealing with loosely packed particles that havevery small primary particles as building blocks.ISSN:1867-1381ISSN:1867-854