Overview and preliminary results of the Surface Ocean Aerosol Production (SOAP) campaign

Establishing the relationship between marine boundary layer (MBL) aerosols and surface water biogeochemistry is required to understand aerosol and cloud production processes over the remote ocean and represent them more accurately in earth system models and global climate projections. This was addressed by the SOAP (Surface Ocean Aerosol Production) campaign, which examined air–sea interaction over biologically productive frontal waters east of New Zealand. This overview details the objectives, regional context, sampling strategy and provisional findings of a pilot study, PreSOAP, in austral summer 2011 and the following SOAP voyage in late austral summer 2012. Both voyages characterized surface water and MBL composition in three phytoplankton blooms of differing species composition and biogeochemistry, with significant regional correlation observed between chlorophyll a and DMSsw. Surface seawater dimethylsulfide (DMSsw) and associated air–sea DMS flux showed spatial variation during the SOAP voyage, with maxima of 25 nmol L−1 and 100 µmol m−2 d−1, respectively, recorded in a dinoflagellate bloom. Inclusion of SOAP data in a regional DMSsw compilation indicates that the current climatological mean is an underestimate for this region of the southwest Pacific. Estimation of the DMS gas transfer velocity (kDMS) by independent techniques of eddy covariance and gradient flux showed good agreement, although both exhibited periodic deviations from model estimates. Flux anomalies were related to surface warming and sea surface microlayer enrichment and also reflected the heterogeneous distribution of DMSsw and the associated flux footprint. Other aerosol precursors measured included the halides and various volatile organic carbon compounds, with first measurements of the short-lived gases glyoxal and methylglyoxal in pristine Southern Ocean marine air indicating an unidentified local source. The application of a real-time clean sector, contaminant markers and a common aerosol inlet facilitated multi-sensor measurement of uncontaminated air. Aerosol characterization identified variable Aitken mode and consistent submicron-sized accumulation and coarse modes. Submicron aerosol mass was dominated by secondary particles containing ammonium sulfate/bisulfate under light winds, with an increase in sea salt under higher wind speeds. MBL measurements and chamber experiments identified a significant organic component in primary and secondary aerosols. Comparison of SOAP aerosol number and size distributions reveals an underprediction in GLOMAP (GLObal Model of Aerosol Processes)-mode aerosol number in clean marine air masses, suggesting a missing marine aerosol source in the model. The SOAP data will be further examined for evidence of nucleation events and also to identify relationships between MBL composition and surface ocean biogeochemistry that may provide potential proxies for aerosol precursors and production

A Mechanism for the Production of Ultrafine Particles from Concrete Fracture

While the crushing of concrete gives rise to large quantities of coarse dust, it is not widely recognized that this process also emits significant quantities of ultrafine particles. These particles impact not just the environments within construction activities but those in entire urban areas. The origin of these ultrafine particles is uncertain, as existing theories do not support their production by mechanical processes. We propose a hypothesis for this observation based on the volatilisation of materials at the concrete fracture interface. The results from this study confirm that mechanical methods can produce ultrafine particles (UFP) from concrete, and that the particles are volatile. The ultrafine mode was only observed during concrete fracture, producing particle size distributions with average count median diameters of 27, 39 and 49 nm for the three tested concrete samples. Further volatility measurements found that the particles were highly volatile, showing between 60 and 95% reduction in the volume fraction remaining by 125 °C. An analysis of the volatile fraction remaining found that different volatile material is responsible for the production of particles between the samples

Ion Beam Analysis (IBA) of submicron nascent Sea Spray Aerosol (SSA) measured during the Surface Ocean Aerosol Production (SOAP) study to the Chatham Rise (east of New Zealand) onboard the RV Tangaroa in 2012

The SOAP voyage examined air-sea interactions over the productive waters of the Chatham Rise, east of New Zealand onboard the RV Tangaroa (New Zealand National Institute of Water and Atmospheric Research, Wellington) from February 12 to March 7 (Law et al., 2017: doi:10.5194/acp-17-13645-2017). 23 seawater samples were collected throughout the voyage for the purpose of generating nascent SSA. Seawater samples were collected from the ocean surface during workboat operations (approximately 10 cm depth) or from the mixed layer (3 - 12 m depth, always less than the measured mixed layer depth) or deep water samples. Surface samples were collected in prewashed 5L PTFE bottles, subsurface measurements were colected in Niskin bottles onboard a CTD rosette. Nascent SSA was generated in-situ in a 0.45 m3 cylindrical polytetrafluoroethylene chamber housing four sintered glass filters with porosities between 16 and 250 μm (Cravigan et al., 2019: https://doi.org/10.5194/acp-2019-797). Dried and filtered compressed air was passed through the glass filters at a flow rate of 15.5 ± 3 L/min and resulting SSA was sampled from the headspace of the chamber. Filters were collected for compositional analysis using transmission Fourier Transform Infra Red (FTIR) and Ion Beam analysis (IBA). The nascent SSA was sampled through a 1 μm sharp cut cyclone (SCC 2.229PM1, BGI Inc., Waltham, Massachusetts) and collected on Teflon filters, with the sample confined to deposit on a 10 mm circular area. Back filter blanks were used to characterise the contamination during handling, and before analysis samples were dehydrated to remove all water, including SSA hydrates, as described in (Frossard and Russell, 2012: doi:10.1021/es3032083). Filter samples underwent simultaneous particle induced X-ray emission (PIXE) and gamma ray emission (PIGE) analysis (Cohen et al., 2004: doi:10.1016/j.nimb.2004.01.043). Si was the only compound with blank measurements above the IBA detection limit. The measured S mass was used to calculate the SO4 mass, all S was assumed to be in the form of SO4. The filter exposed area (0.785 cm2) was used to convert inorganic areal concentrations into total mass. The inorganic mass (IM) was computed as the sum of Na, Mg, SO4, Cl, K, Ca, Zn, Br and Sr. The seawater chlorophyll-a concentration was measured by filtering 2 litres of sample water onto GF/F Whatman filters, with immediate freezing in liquid nitrogen and subsequent analysis within 3 months of collection. Filters were ground and chlorophyll-a extracted in 90 % acetone with concentration determined by a calibrated fluorometer (Perkin-Elmer), with an analytical precision of 0.001 mg/m3 (Law et al., 2011: doi:10.1016/j.dsr2.2010.10.018)

Organic volume fraction and hygroscopic growth factor of nascent Sea Spray Aerosol (SSA) measured using VH-TDMA during the Surface Ocean Aerosol Production (SOAP) study to the Chatham Rise (east of New Zealand) onboard the RV Tangaroa in 2012

The SOAP voyage examined air-sea interactions over the productive waters of the Chatham Rise, east of New Zealand onboard the RV Tangaroa (New Zealand National Institute of Water and Atmospheric Research, Wellington) from February 12 to March 7 (Law et al., 2017: doi:10.5194/acp-17-13645-2017). 23 seawater samples were collected throughout the voyage for the purpose of generating nascent SSA. Seawater samples were collected from the ocean surface during workboat operations (approximately 10 cm depth) or from the mixed layer (3 - 12 m depth, always less than the measured mixed layer depth) or deep water samples. Surface samples were collected in prewashed 5L PTFE bottles, subsurface measurements were colected in Niskin bottles onboard a CTD rosette. Nascent SSA was generated in-situ in a 0.45 m3 cylindrical polytetrafluoroethylene chamber housing four sintered glass filters with porosities between 16 and 250 μm (Cravigan et al., 2019: https://doi.org/10.5194/acp-2019-797). Dried and filtered compressed air was passed through the glass filters at a flow rate of 15.5 ± 3 L/min and resulting SSA was sampled from the headspace of the chamber. The volatility and hygroscopicity of nascent SSA was determined with a volatility and hygroscopicity tandem differential mobility analyser (VH-TDMA) (Johnson et al., 2004: doi:10.1016/j.jaerosci.2003.10.008, 2008: doi:10.1016/j.jaerosci.2008.05.005). A diffusion drier was used to dry the sample flow to 20 ± 5 % RH prior to characterisation by the VH-TDMA. The VH-TDMA was also used to calculate the organic volume fraction (Cravigan et al., 2019: https://doi.org/10.5194/acp-2019-797). The VH-TDMA used two TSI 3010 condensation particle counters. The aerosol sample flow rate for each scanning mobility particle sizer was 1 L/min, resulting in a total inlet flow of 2 L/min, the sheath flow for the pre-DMA, V-DMA and H-DMA were 11, 6 and 6 L/min, respectively. The SSA volatile fraction was computed by measuring the diameter of preselected SSA upon heating by a thermodenuder up to 500 degree C, in temperature increments of 5 degree C - 50 degree C. After heating the SSA hygroscopic growth factor at 90% RH was measured. All VH-TDMA data were inverted using the TDMAinv algorithm (Gysel et al., 2009: doi:10.1016/j.jaerosci.2008.07.013). The hygroscopic growth factor, semi-volatile organic volume fraction and low volatility organic volume fraction were determined as outlined in (Cravigan et al., 2019: doi:10.5194/acp-2019-797). The seawater chlorophyll-a concentration was measured by filtering 2 litres of sample water onto GF/F Whatman filters, with immediate freezing in liquid nitrogen and subsequent analysis within 3 months of collection. Filters were ground and chlorophyll-a extracted in 90 % acetone with concentration determined by a calibrated fluorometer (Perkin-Elmer), with an analytical precision of 0.001 mg/m3 (Law et al., 2011: doi:10.1016/j.dsr2.2010.10.018)

Deliquescence of nascent Sea Spray Aerosol (SSA) measured using VH-TDMA during the Surface Ocean Aerosol Production (SOAP) study to the Chatham Rise onboard the RV Tangaroa in 2012

The SOAP voyage examined air-sea interactions over the productive waters of the Chatham Rise, east of New Zealand onboard the RV Tangaroa (New Zealand National Institute of Water and Atmospheric Research, Wellington) from February 12 to March 7 (Law et al., 2017: doi:10.5194/acp-17-13645-2017). 23 seawater samples were collected throughout the voyage for the purpose of generating nascent SSA. Seawater samples were collected from the ocean surface during workboat operations (approximately 10 cm depth) or from the mixed layer (3 - 12 m depth, always less than the measured mixed layer depth) or deep water samples. Surface samples were collected in prewashed 5L PTFE bottles, subsurface measurements were colected in Niskin bottles onboard a CTD rosette. Nascent SSA was generated in-situ in a 0.45 m3 cylindrical polytetrafluoroethylene chamber housing four sintered glass filters with porosities between 16 and 250 μm (Cravigan et al., 2019: https://doi.org/10.5194/acp-2019-797). Dried and filtered compressed air was passed through the glass filters at a flow rate of 15.5 ± 3 L/min and resulting SSA was sampled from the headspace of the chamber. The volatility and hygroscopicity of nascent SSA was determined with a volatility and hygroscopicity tandem differential mobility analyser (VH-TDMA) (Johnson et al., 2004: doi:10.1016/j.jaerosci.2003.10.008, 2008: doi:10.1016/j.jaerosci.2008.05.005). A diffusion drier was used to dry the sample flow to 20 ± 5 % RH prior to characterisation by the VH-TDMA. The VH-TDMA used two TSI 3010 condensation particle counters. The aerosol sample flow rate for each scanning mobility particle sizer was 1 L/min, resulting in a total inlet flow of 2 L/min, the sheath flow for the pre-DMA, V-DMA and H-DMA were 11, 6 and 6 L/min, respectively. The dependence of HGF on RH at ambient temperature was measured for one water sample (workboat 9) to provide the deliquescence relative humidity (DRH). All VH-TDMA data were inverted using the TDMAinv algorithm (Gysel et al., 2009: doi:10.1016/j.jaerosci.2008.07.013). The seawater chlorophyll-a concentration was measured by filtering 2 litres of sample water onto GF/F Whatman filters, with immediate freezing in liquid nitrogen and subsequent analysis within 3 months of collection. Filters were ground and chlorophyll-a extracted in 90 % acetone with concentration determined by a calibrated fluorometer (Perkin-Elmer), with an analytical precision of 0.001 mg/m3 (Law et al., 2011: doi:10.1016/j.dsr2.2010.10.018)

Fourier Transform Infra-Red spectroscopy (FTIR) of submicron nascent Sea Spray Aerosol (SSA) measured during the Surface Ocean Aerosol Production (SOAP) study to the Chatham Rise (east of New Zealand) onboard the RV Tangaroa in 2012

The SOAP voyage examined air-sea interactions over the productive waters of the Chatham Rise, east of New Zealand onboard the RV Tangaroa (New Zealand National Institute of Water and Atmospheric Research, Wellington) from February 12 to March 7 (Law et al., 2017: doi:10.5194/acp-17-13645-2017). 23 seawater samples were collected throughout the voyage for the purpose of generating nascent SSA. Seawater samples were collected from the ocean surface during workboat operations (approximately 10 cm depth) or from the mixed layer (3 - 12 m depth, always less than the measured mixed layer depth) or deep water samples. Surface samples were collected in prewashed 5L PTFE bottles, subsurface measurements were colected in Niskin bottles onboard a CTD rosette. Nascent SSA was generated in-situ in a 0.45 m3 cylindrical polytetrafluoroethylene chamber housing four sintered glass filters with porosities between 16 and 250 μm (Cravigan et al., 2019: https://doi.org/10.5194/acp-2019-797). Dried and filtered compressed air was passed through the glass filters at a flow rate of 15.5 ± 3 L/min and resulting SSA was sampled from the headspace of the chamber. Filters were collected for compositional analysis using transmission Fourier Transform Infra Red (FTIR) and Ion Beam analysis (IBA). The nascent SSA was sampled through a 1 μm sharp cut cyclone (SCC 2.229PM1, BGI Inc., Waltham, Massachusetts) and collected on Teflon filters, with the sample confined to deposit on a 10 mm circular area. Back filter blanks were used to characterise the contamination during handling, and before analysis samples were dehydrated to remove all water, including SSA hydrates, as described in (Frossard and Russell, 2012: doi:10.1021/es3032083). FTIR measurements were carried out according to previous marine sampling techniques (Maria et al., 2003: doi:10.1029/2003jd003703; Russell et al., 2010: doi:10.1073/pnas.0908905107). Filter blanks were under the detection limit for the FTIR. The PM1 organic mass fraction from SSA samples collected on filters was computed from the total organic mass from FTIR analysis and the inorganic mass from ion beam analysis, as in (Cravigan et al., 2019: doi:10.5194/acp-2019-797). The uncertainty in the organic mass measured using FTIR is up to 20 % (Maria et al., 2003: doi:10.1029/2003jd003703; Russell et al., 2010: doi:10.1073/pnas.0908905107). The seawater chlorophyll-a concentration was measured by filtering 2 litres of sample water onto GF/F Whatman filters, with immediate freezing in liquid nitrogen and subsequent analysis within 3 months of collection. Filters were ground and chlorophyll-a extracted in 90 % acetone with concentration determined by a calibrated fluorometer (Perkin-Elmer), with an analytical precision of 0.001 mg/m3 (Law et al., 2011: doi:10.1016/j.dsr2.2010.10.018)

Sea spray aerosol organic enrichment, water uptake and surface tension effects

The aerosol-driven radiative effects on marine low-level cloud represent a large uncertainty in climate simulations, in particular over the Southern Ocean, which is also an important region for sea spray aerosol production. Observations of sea spray aerosol organic enrichment and the resulting impact on water uptake over the remote Southern Hemisphere are scarce, and therefore the region is underrepresented in existing parameterisations. The Surface Ocean Aerosol Production (SOAP) voyage was a 23 d voyage which sampled three phytoplankton blooms in the highly productive water of the Chatham Rise, east of New Zealand. In this study we examined the enrichment of organics to nascent sea spray aerosol and the modifications to sea spray aerosol water uptake using in situ chamber measurements of seawater samples taken during the SOAP voyage. Primary marine organics contributed up to 23% of the sea spray mass for particles with diameter less than approximately 1 m and up to 79% of the particle volume for 50 nm diameter sea spray. The composition of the submicron organic fraction was consistent throughout the voyage and was largely composed of a polysaccharide-like component, characterised by very low alkane-to-hydroxylconcentration ratios of approximately 0.1 0.2. The enrichment of organics was compared to the output from the chlorophyll-a-based sea spray aerosol parameterisation suggested by Gantt et al. (2011) and the OCEANFILMS (Organic Compounds from Ecosystems to Aerosols: Natural Films and Interfaces via Langmuir Molecular Surfactants) models. OCEANFILMS improved on the representation of the organic fraction predicted using chlorophyll a, in particular when the co-adsorption of polysaccharides was included; however, the model still under-predicted the proportion of polysaccharides by an average of 33 %. Nascent 50 nm diameter sea spray aerosol hygroscopic growth factors measured at 90% relative humidity averaged 1:930:08 and did not decrease with increasing sea spray aerosol organic fractions. The observed hygroscopicity was greater than expected from the assumption of full solubility, particularly during the most productive phytoplankton bloom (B1), during which organic fractions were greater than approximately 0.4. The water uptake behaviour observed in this study is consistent with that observed for other measurements of phytoplankton blooms and can be partially attributed to the presence of sea salt hydrates, which lowers the sea spray aerosol hygroscopicity when the organic enrichment is low. The inclusion of surface tension effects only marginally improved the modelled hygroscopicity, and a significant discrepancy between the observed and modelled hygroscopicity at high organic volume fractions remained. The findings from the SOAP voyage highlight the influence of biologically sourced organics on sea spray aerosol composition; these data improve the capacity to parameterise sea spray aerosol organic enrichment and water uptake. </p

The contribution of coral-reef-derived dimethyl sulfide to aerosol burden over the Great Barrier Reef : A modelling study

Coral reefs have been found to produce the sulfur compound dimethyl sulfide (DMS), a climatically relevant aerosol precursor predominantly associated with phytoplankton. Until recently, the role of coral-reef-derived DMS within the climate system had not been quantified. A study preceding the present work found that DMS produced by corals had negligible long-term climatic forcing at the global-regional scale. However, at sub-daily timescales more typically associated with aerosol and cloud formation, the influence of coral-reef-derived DMS on local aerosol radiative effects remains unquantified. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) has been used in this work to study the role of coral-reef-derived DMS at sub-daily timescales for the first time. WRF-Chem was run to coincide with an October 2016 field campaign over the Great Barrier Reef, Queensland, Australia, against which the model was evaluated. After updating and scaling the DMS surface water climatology, the model reproduced DMS and sulfur concentrations well. The inclusion of coral-reef-derived DMS resulted in no significant change in sulfate aerosol mass or total aerosol number. Subsequently, no direct or indirect aerosol effects were detected. The results suggest that the co-location of the Great Barrier Reef with significant anthropogenic aerosol sources along the Queensland coast prevents coral-reef-derived aerosol from having a modulating influence on local aerosol burdens in the current climate.</p

Biomass burning emissions in north Australia during the early dry season: An overview of the 2014 SAFIRED campaign

© 2017 Author(s). The SAFIRED (Savannah Fires in the Early Dry Season) campaign took place from 29 May until 30 June 2014 at the Australian Tropical Atmospheric Research Station (ATARS) in the Northern Territory, Australia. The purpose of this campaign was to investigate emissions from fires in the early dry season in northern Australia. Measurements were made of biomass burning aerosols, volatile organic compounds, polycyclic aromatic carbons, greenhouse gases, radon, speciated atmospheric mercury and trace metals. Aspects of the biomass burning aerosol emissions investigated included; emission factors of various species, physical and chemical aerosol properties, aerosol aging, micronutrient supply to the ocean, nucleation, and aerosol water uptake. Over the course of the month-long campaign, biomass burning signals were prevalent and emissions from several large single burning events were observed at ATARS.&lt;br&gt;&lt;br&gt;Biomass burning emissions dominated the gas and aerosol concentrations in this region. Dry season fires are extremely frequent and widespread across the northern region of Australia, which suggests that the measured aerosol and gaseous emissions at ATARS are likely representative of signals across the entire region of north Australia. Air mass forward trajectories show that these biomass burning emissions are carried north-west over the Timor Sea and could influence the atmosphere over Indonesia and the tropical atmosphere over the Indian Ocean. Here we present characteristics of the biomass burning observed at the sampling site and provide an overview of the more specific outcomes of the SAFIRED campaign

Observations of clouds, aerosols, precipitation, and surface radiation over the Southern Ocean: An overview of CAPRICORN, MARCUS, MICRE and SOCRATES

Weather and climate models are challenged by uncertainties and biases in simulating Southern Ocean (SO) radiative fluxes that trace to a poor understanding of cloud, aerosol, precipitation, and radiative processes, and their interactions. Projects between 2016 and 2018 used in situ probes, radar, lidar, and other instruments to make comprehensive measurements of thermodynamics, surface radiation, cloud, precipitation, aerosol, cloud condensation nuclei (CCN), and ice nucleating particles over the SO cold waters, and in ubiquitous liquid and mixed-phase clouds common to this pristine environment. Data including soundings were collected from the NSF–NCAR G-V aircraft flying north–south gradients south of Tasmania, at Macquarie Island, and on the R/V Investigator and RSV Aurora Australis. Synergistically these data characterize boundary layer and free troposphere environmental properties, and represent the most comprehensive data of this type available south of the oceanic polar front, in the cold sector of SO cyclones, and across seasons. Results show largely pristine environments with numerous small and few large aerosols above cloud, suggesting new particle formation and limited long-range transport from continents, high variability in CCN and cloud droplet concentrations, and ubiquitous supercooled water in thin, multilayered clouds, often with small-scale generating cells near cloud top. These observations demonstrate how cloud properties depend on aerosols while highlighting the importance of dynamics and turbulence that likely drive heterogeneity of cloud phase. Satellite retrievals confirmed low clouds were responsible for radiation biases. The combination of models and observations is examining how aerosols and meteorology couple to control SO water and energy budgets