Multi-campaign ship and aircraft observations of marine cloud condensation nuclei and droplet concentrations.

In-situ marine cloud droplet number concentrations (CDNCs), cloud condensation nuclei (CCN), and CCN proxies, based on particle sizes and optical properties, are accumulated from seven field campaigns: ACTIVATE; NAAMES; CAMP2EX; ORACLES; SOCRATES; MARCUS; and CAPRICORN2. Each campaign involves aircraft measurements, ship-based measurements, or both. Measurements collected over the North and Central Atlantic, Indo-Pacific, and Southern Oceans, represent a range of clean to polluted conditions in various climate regimes. With the extensive range of environmental conditions sampled, this data collection is ideal for testing satellite remote detection methods of CDNC and CCN in marine environments. Remote measurement methods are vital to expanding the available data in these difficult-to-reach regions of the Earth and improving our understanding of aerosol-cloud interactions. The data collection includes particle composition and continental tracers to identify potential contributing CCN sources. Several of these campaigns include High Spectral Resolution Lidar (HSRL) and polarimetric imaging measurements and retrievals that will be the basis for the next generation of space-based remote sensors and, thus, can be utilized as satellite surrogates.

Use of portable air cleaners to reduce aerosol transmission on a hospital coronavirus disease 2019 (COVID-19) ward.

OBJECTIVE: To study the airflow, transmission, and clearance of aerosols in the clinical spaces of a hospital ward that had been used to care for patients with coronavirus disease 2019 (COVID-19) and to examine the impact of portable air cleaners on aerosol clearance. DESIGN: Observational study. SETTING: A single ward of a tertiary-care public hospital in Melbourne, Australia. INTERVENTION: Glycerin-based aerosol was used as a surrogate for respiratory aerosols. The transmission of aerosols from a single patient room into corridors and a nurses' station in the ward was measured. The rate of clearance of aerosols was measured over time from the patient room, nurses' station and ward corridors with and without air cleaners [ie, portable high-efficiency particulate air (HEPA) filters]. RESULTS: Aerosols rapidly travelled from the patient room into other parts of the ward. Air cleaners were effective in increasing the clearance of aerosols from the air in clinical spaces and reducing their spread to other areas. With 2 small domestic air cleaners in a single patient room of a hospital ward, 99% of aerosols could be cleared within 5.5 minutes. CONCLUSIONS: Air cleaners may be useful in clinical spaces to help reduce the risk of acquisition of respiratory viruses that are transmitted via aerosols. They are easy to deploy and are likely to be cost-effective in a variety of healthcare settings.

Atmospheric reactive mercury concentrations in coastal Australia and the Southern Ocean.

Mercury (Hg), especially reactive Hg (RM), data from the Southern Hemisphere (SH) are limited. In this study, long-term measurements of both gaseous elemental Hg (GEM) and RM were made at two ground-based monitoring locations in Australia, the Cape Grim Baseline Air Pollution Station (CGBAPS) in Tasmania, and the Macquarie University Automatic Weather Station (MQAWS) in Sydney, New South Wales. Measurements were also made on board the Australian RV Investigator (RVI) during an ocean research voyage to the East Antarctic coast. GEM was measured using the standard Tekran® 2537 series analytical platform, and RM was measured using cation exchange membranes (CEM) in a filter-based sampling method. Overall mean RM concentrations at CGBAPS and MQAWS were 15.9 ± 6.7 pg m-3 and 17.8 ± 6.6 pg m-3, respectively. For the 10-week austral summer period on RVI, mean RM was 23.5 ± 6.7 pg m-3. RM concentrations at CGBAPS were seasonally invariable, while those at MQAWS were significantly different between summer and winter due to seasonal changes in synoptic wind patterns. During the RVI voyage, RM concentrations were relatively enhanced along the Antarctic coast (up to 30 pg m-3) and GEM concentrations were variable (0.2 to 0.9 ng m-3), suggesting periods of enrichment and depletion. Both RM and GEM concentrations were relatively lower while transiting the Southern Ocean farther north of Antarctica. RM concentrations measured in this study were higher in comparison to most other reported measurements of RM in the global marine boundary layer (MBL), especially for remote SH locations. As observations of GEM and RM concentrations inform global ocean-atmosphere model simulations of the atmospheric Hg budget, our results have important implications for understanding of total atmospheric Hg (TAM).

Aerosol generation related to respiratory interventions and the effectiveness of a personal ventilation hood.

OBJECTIVE: To quantify aerosol generation from respiratory interventions and the effectiveness of their removal by a personal ventilation hood. DESIGN AND SETTING: Determination of the aerosol particle generation (in a single, healthy volunteer in a clean room) associated with breathing, speaking, wet coughing, oxygen (O2) 15 L/min via face mask, O2 60 L/min via nasal prongs, bilevel non-invasive positive-pressure ventilation (BiPAP) and nebulisation with O2 10 L/min. INTERVENTIONS: Aerosol generation was measured with two particle sizer and counter devices, focusing on aerosols 0.5-5 µm (human-generated aerosols), with and without the hood. An increase from baseline of less than 0.3 particles per mL was considered a low level of generation. MAIN OUTCOME MEASURES: Comparisons of aerosol generation between different respiratory interventions. Effectiveness of aerosol reduction by a personal ventilation hood. RESULTS: Results for the 0.5-5 µm aerosol range. Quiet breathing and talking demonstrated very low increase in aerosols (< 0.1 particles/mL). Aerosol generation was low for wet coughing (0.1 particles/mL), O2 15 L/min via face mask (0.18 particles/mL), and high flow nasal O2 60 L/min (0.24 particles/mL). Non-invasive ventilation generated moderate aerosols (29.7 particles/mL) and nebulisation very high aerosols (1086 particles/mL); the personal ventilation hood reduced the aerosol counts by 98% to 0.5 particles/mL and 8.9 particles/mL respectively. CONCLUSIONS: In this human volunteer study, the administration of O2 15 L/min by face mask and 60 L/min nasal therapy did not increase aerosol generation beyond low levels. Non-invasive ventilation caused moderate aerosol generation and nebulisation therapy very high aerosol generation. The personal ventilation hood reduced the aerosol counts by at least 98%.

Characterization of aerosols over the Great Barrier Reef: The influence of transported continental sources.

The rapid environmental changes in Australia prompt a more thorough investigation of the influence of transportation, local emissions, and optical-chemical properties on aerosol production across the region. A month-long intensive measurement campaign was conducted during spring 2016 at Mission Beach, a remote coastal site west of the Great Barrier Reef (GBR) on the north-east coast of Australia. One aerosol pollution episode was investigated in early October. This event was governed by meteorological conditions and characterized by the increase in black carbon (BC) mass concentration (averaged value of 0.35 ±â€¯0.20 µg m-3). Under the influence of the continental transportation, a new layer of nucleation-mode aerosols with an initial size diameter of 20 nm was observed and aerosol number concentrations reached the peak of 6733 cm-3 at a diameter of 29 nm. The averaged aerosol extinction coefficient at the height of 2 km was 150 Mm-1, with a small depolarized ratio (3.5-5%). Simultaneously, the boundary layer height presented a fall-rise trend in the presence of these enhanced aerosol concentrations and became stable in a later stage of the episode. We did not observe clear boundary layer height diurnal variations from the LiDAR observations or from the Weather Research and Forecasting (WRF) model outputs, except in an earlier stage of the aerosol episode for the former. Although the sea breeze may have been responsible for these particles, on the balance of available data, we suggest that the aerosol properties at the GBR surface during this period are more likely influenced by regional transportation of continental sources, including biomass-burning aerosols.

Emission Factors for Selected Semivolatile Organic Chemicals from Burning of Tropical Biomass Fuels and Estimation of Annual Australian Emissions.

This study reveals that open-field biomass burning can be an important source of various semivolatile organic chemicals (SVOCs) to the atmosphere including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and a range of pesticides. Emission factors (EFs) for 39 individual SVOCs are determined from burning of various fuel types that are common in tropical Australia. Emissions of PAHs are found to be sensitive to differences in combustion efficiencies rather than fuel types, reflecting a de novo formation mechanism. In contrast, revolatilization may be important for other SVOCs such as PCBs. On the basis of the EFs determined in this work, estimates of the annual emissions of these SVOCs from Australian bushfires/wildfires are achieved, including, for example, ∑PAHs (160 (min)-1100 (max) Mg), ∑PCBs (14-300 kg), ∑PBDEs (8.8-590 kg), α-endosulfan (6.5-200 kg), and chlorpyrifos (up to 1400 kg), as well as dioxin toxic equivalents (TEQs) of ∑dioxin-like-PCBs (0.018-1.4 g). Emissions of SVOCs that are predominantly revolatilized appear to be related to their use history, with higher emissions estimated for chemicals that had a greater historical usage and were banned only recently or are still in use.

Emissions of Selected Semivolatile Organic Chemicals from Forest and Savannah Fires.

The emission factors (EFs) for a broad range of semivolatile organic chemicals (SVOCs) from subtropical eucalypt forest and tropical savannah fires were determined for the first time from in situ investigations. Significantly higher (t test, P < 0.01) EFs (µg kg-1 dry fuel, gas + particle-associated) for polycyclic aromatic hydrocarbons (∑13 PAHs) were determined from the subtropical forest fire (7,000 ± 170) compared to the tropical savannah fires (1,600 ± 110), due to the approximately 60-fold higher EFs for 3-ring PAHs from the former. EF data for many PAHs from the eucalypt forest fire were comparable with those previously reported from pine and fir forest combustion events. EFs for other SVOCs including polychlorinated biphenyl (PCB), polychlorinated naphthalene (PCN), and polybrominated diphenyl ether (PBDE) congeners as well as some pesticides (e.g., permethrin) were determined from the subtropical eucalypt forest fire. The highest concentrations of total suspended particles, PAHs, PCBs, PCNs, and PBDEs, were typically observed in the flaming phase of combustion. However, concentrations of levoglucosan and some pesticides such as permethrin peaked during the smoldering phase. Along a transect (10-150-350 m) from the forest fire, concentration decrease for PCBs during flaming was faster compared to PAHs, while levoglucosan concentrations increased.

New particle formation in China: Current knowledge and further directions.

New particle formation (NPF) studies have been conducted in China since 2004. Formation of new atmospheric aerosol particles has been observed to take place in diverse environments, even under the circumstances of high pre-existing particle loading, challenging the traditional and present understanding of the physicochemical nucleation mechanisms, which have been proposed based on the investigations in clean environments and under laboratory experimental conditions. This paper summarizes the present status and gaps in understanding NPF in China and discusses the main directions opening for future research.

Forest Fire Smoke Exposures and Out-of-Hospital Cardiac Arrests in Melbourne, Australia: A Case-Crossover Study.

BACKGROUND: Millions of people can potentially be exposed to smoke from forest fires, making this an important public health problem in many countries. OBJECTIVE: In this study we aimed to measure the association between out-of-hospital cardiac arrest (OHCA) and forest fire smoke exposures in a large city during a severe forest fire season, and estimate the number of excess OHCAs due to the fire smoke. METHODS: We investigated the association between particulate matter (PM) and other air pollutants and OHCA using a case-crossover study of adults (≥ 35 years of age) in Melbourne, Australia. Conditional logistic regression models were used to derive estimates of the percent change in the rate of OHCA associated with an interquartile range (IQR) increase in exposure. From July 2006 through June 2007, OHCA data were collected from the Victorian Ambulance Cardiac Arrest Registry. Hourly air pollution concentrations and meteorological data were obtained from a central monitoring site. RESULTS: There were 2,046 OHCAs with presumed cardiac etiology during our study period. Among men during the fire season, greater increases in OHCA were observed with IQR increases in the 48-hr lagged PM with diameter ≤ 2.5 µm (PM2.5) (8.05%; 95% CI: 2.30, 14.13%; IQR = 6.1 µg/m(3)) or ≤ 10 µm (PM10) (11.1%; 95% CI: 1.55, 21.48%; IQR = 13.7 µg/m(3)) and carbon monoxide (35.7%; 95% CI: 8.98, 68.92%; IQR = 0.3 ppm). There was no significant association between the rate of OHCA and air pollutants among women. One hundred seventy-four "fire-hours" (i.e., hours in which Melbourne's air quality was affected by forest fire smoke) were identified during 12 days of the 2006/2007 fire season, and 23.9 (95% CI: 3.1, 40.2) excess OHCAs were estimated to occur due to elevations in PM2.5 during these fire-hours. CONCLUSIONS: This study found an association between exposure to forest fire smoke and an increase in the rate of OHCA. These findings have implications for public health messages to raise community awareness and for planning of emergency services during forest fire seasons.

Spatial distribution of selected persistent organic pollutants (POPs) in Australia's atmosphere.

A nation-wide passive air sampling campaign recorded concentrations of persistent organic pollutants in Australia's atmosphere in 2012. XAD-based passive air samplers were deployed for one year at 15 sampling sites located in remote/background, agricultural and semi-urban and urban areas across the continent. Concentrations of 47 polychlorinated biphenyls ranged from 0.73 to 72 pg m(-3) (median of 8.9 pg m(-3)) and were consistently higher at urban sites. The toxic equivalent concentration for the sum of 12 dioxin-like PCBs was low, ranging from below detection limits to 0.24 fg m(-3) (median of 0.0086 fg m(-3)). Overall, the levels of polychlorinated biphenyls in Australia were among the lowest reported globally to date. Among the organochlorine pesticides, hexachlorobenzene had the highest (median of 41 pg m(-3)) and most uniform concentration (with a ratio between highest and lowest value ∼5). Bushfires may be responsible for atmospheric hexachlorobenzene levels in Australia that exceeded Southern Hemispheric baseline levels by a factor of ∼4. Organochlorine pesticide concentrations generally increased from remote/background and agricultural sites to urban sites, except for high concentrations of α-endosulfan and DDTs at specific agricultural sites. Concentrations of heptachlor (0.47-210 pg m(-3)), dieldrin (ND-160 pg m(-3)) and trans- and cis-chlordanes (0.83-180 pg m(-3), sum of) in Australian air were among the highest reported globally to date, whereas those of DDT and its metabolites (ND-160 pg m(-3), sum of), α-, ß-, γ- and δ-hexachlorocyclohexane (ND-6.7 pg m(-3), sum of) and α-endosulfan (ND-27 pg m(-3)) were among the lowest.

Diaterebic acid acetate and diaterpenylic acid acetate: atmospheric tracers for secondary organic aerosol formation from 1,8-cineole oxidation.

Detailed organic speciation of summer time PM10 collected in Melbourne, Australia, indicated the presence of numerous monoterpene oxidation products that have previously been reported in the literature. In addition, two highly oxygenated compounds with molecular formulas C9H14O6 (MW 218) and C10H16O6 (MW 232), previously unreported, were detected during a period associated with high temperatures and bushfire smoke. These two compounds were also present in laboratory-produced secondary organic aerosol (SOA) through the reaction of OH radicals with 1,8-cineole (eucalyptol), which is emitted by Eucalyptus trees. The retention times and mass spectral behavior of the highly oxygenated compounds in high-performance liquid chromatography (LC) coupled to electrospray ionization-time-of-flight mass spectrometry (MS) in parallel to ion trap MS of agree perfectly between the ambient samples and the laboratory-produced SOA samples, suggesting that 1,8-cineole is the precursor of the highly oxygenated compounds. The proposed structure of the compound with molecular formula C10H16O6 was confirmed by synthesis of a reference compound. The two novel compounds were identified as diaterebic acid acetate (2-[1-(acetyloxy)-1-methylethyl]succinic acid, C9H14O6) and diaterpenylic acid acetate (3-[1-(acetyloxy)-1-methylethyl]glutaric acid, C10H16O6) based on the consideration of reaction mechanisms, the structure of a reference compound, and the interpretation of mass spectral data. Depending on the experimental conditions, the SOA yields determined in chamber experiments ranged between 16 and 20% for approximately 25 ppb of hydrocarbon consumed. The concentrations of these compounds were as high as 50 ng m(-3) during the summertime in Melbourne. This study demonstrates the importance and influence of local vegetation patterns on SOA chemical composition.

Contribution of first- versus second-generation products to secondary organic aerosols formed in the oxidation of biogenic hydrocarbons.

Biogenic hydrocarbons emitted by vegetation are important contributors to secondary organic aerosol (SOA), but the aerosol formation mechanisms are incompletely understood. In this study, the formation of aerosols and gas-phase products from the ozonolysis and photooxidation of a series of biogenic hydrocarbons (isoprene, 8 monoterpenes, 4 sesquiterpenes, and 3 oxygenated terpenes) are examined. By comparing aerosol growth (measured by Differential Mobility Analyzers, DMAs) and gas-phase concentrations (monitored by a Proton Transfer Reaction Mass Spectrometer, PTR-MS), we study the general mechanisms of SOA formation. Aerosol growth data are presented in terms of a "growth curve", a plot of aerosol mass formed versus the amount of hydrocarbon reacted. From the shapes of the growth curves, it is found that all the hydrocarbons studied can be classified into two groups based entirely on the number of double bonds of the hydrocarbon, regardless of the reaction systems (ozonolysis or photooxidation) and the types of hydrocarbons studied: compounds with only one double bond and compounds with more than one double bond. For compounds with only one double bond, the first oxidation step is rate-limiting, and aerosols are formed mainly from low volatility first-generation oxidation products; whereas for compounds with more than one double bond, the second oxidation step may also be rate-limiting and second-generation products contribute substantially to SOA growth. This behavior is characterized by a vertical section in the growth curve, in which continued aerosol growth is observed even after all the parent hydrocarbon is consumed.

Particle phase acidity and oligomer formation in secondary organic aerosol.

A series of controlled laboratory experiments are carried out in dual Teflon chambers to examine the presence of oligomers in secondary organic aerosols (SOA) from hydrocarbon ozonolysis as well as to explore the effect of particle phase acidity on SOA formation. In all seven hydrocarbon systems studied (i.e., alpha-pinene, cyclohexene, 1-methyl cyclopentene, cycloheptene, 1-methyl cyclohexene, cyclooctene, and terpinolene), oligomers with MW from 250 to 1600 are present in the SOA formed, both in the absence and presence of seed particles and regardless of the seed particle acidity. These oligomers are comparable to, and in some cases, exceed the low molecular weight species (MW < 250) in ion intensities in the ion trap mass spectra, suggesting they may comprise a substantial fraction of the total aerosol mass. It is possible that oligomers are widely present in atmospheric organic aerosols, formed through acid- or base-catalyzed heterogeneous reactions. In addition, as the seed particle acidity increases, larger oligomers are formed more abundantly in the SOA; consequently, the overall SOA yield also increases. This explicit effect of particle phase acidity on the composition and yield of SOA may have important climatic consequences and need to be considered in relevant models.