Measurements of aerosol composition and size distributions were taken during
the summer of 2013 at the remote island of Lampedusa in the southern central
Mediterranean Sea. These measurements were ...part of the ChArMEx/ADRIMED
(Chemistry and Aerosol Mediterranean Experiment/Aerosol Direct Radiative
Forcing on the Mediterranean Climate) framework and took place during
Special Observation Period 1a (SOP-1a) from 11 June to 5 July 2013. From compact time-of-flight aerosol mass spectrometer (cToF-AMS)
measurements in the size range below 1 µm in aerodynamic diameter
(PM1), particles were predominately comprised of ammonium and sulfate. On
average, ammonium sulfate contributed 63 % to the non-refractory PM1
mass, followed by organics (33 %). The organic aerosol was generally very
highly oxidized (f44 values were typically between 0.25 and 0.26). The
contribution of ammonium sulfate was generally higher than organic aerosol
in comparison to measurements taken in the western Mediterranean but is
consistent with studies undertaken in the eastern basin. Source apportionment of organics using a statistical (positive matrix
factorization) model revealed four factors: a hydrocarbon-like organic
aerosol (HOA), a methanesulfonic-acid-related oxygenated organic aerosol
(MSA-OOA), a more oxidized oxygenated organic aerosol (MO-OOA) and a less
oxidized oxygenated organic aerosol (LO-OOA). The MO-OOA was the
dominant factor for most of the campaign (53 % of the PM1 OA mass). It was
well correlated with SO42-, highly oxidized and generally more
dominant during easterly air masses originating from the eastern
Mediterranean and central Europe. The LO-OOA factor had a very similar
composition to the MO-OOA factor but was more prevalent during westerly
winds, with air masses originating from the Atlantic Ocean, the western
Mediterranean and at high altitudes over France and Spain from mistral
winds. The MSA-OOA factor contributed an average 12 % to the PM1 OA and
was more dominant during the mistral winds. The HOA, representing observed
primary organic aerosol, only contributed 8 % of the average PM1 OA during
the campaign. Even though Lampedusa is one of the most remote sites in the Mediterranean,
PM1 concentrations (10 ± 5 µg m−3) were comparable to those
observed in coastal cities and sites closer to continental Europe. Cleaner
conditions corresponded to higher wind speeds. Nucleation and growth of new
aerosol particles was observed during periods of north-westerly winds. From a
climatology analysis from 1999 to 2012, these periods were much more
prevalent during the measurement campaign than during the preceding 13 years.
These results support previous findings that highlight the importance
of different large-scale synoptic conditions in determining the regional and
local aerosol composition and oxidation and also suggest that a non-polluted
surface atmosphere over the Mediterranean is rare.
Sea spray aerosol (SSA) particles produced from the ocean surface in regions of biological activity can vary greatly in size, number and composition, and in their influence on cloud formation. Algal ...species such as phytoplankton can alter the SSA composition. Numerous studies have investigated nascent SSA properties, but all of these have focused on aerosol particles produced by seawater from noncoral related phytoplankton and in coastal regions. Bubble chamber experiments were performed with seawater samples taken from the reef flat around Heron Island in the Great Barrier Reef during winter 2011. Here we show that the SSA from these samples was composed of an internal mixture of varying fractions of sea salt, semivolatile organics, as well as nonvolatile (below 550°C) organics. A relatively constant volume fraction of semivolatile organics of 10%–13% was observed, while nonvolatile organic volume fractions varied from 29% to 49% for 60 nm SSA. SSA organic fractions were estimated to reduce the activation ratios of SSA to cloud condensation nuclei by up to 14% when compared with artificial sea salt. Additionally, a sea‐salt calibration was applied so that a compact time‐of‐flight aerosol mass spectrometer could be used to quantify the contribution of sea salt to submicron SSA, which yielded organic volume fractions of 3%–6%. Overall, these results indicate a high fraction of organics associated with wintertime Aitken mode SSA generated from Great Barrier Reef seawater. Further work is required to fully distinguish any differences coral reefs have on SSA composition when compared to open oceans.
Key Points
Organics in the Great Barrier Reef can influence sea spray aerosol composition
Coral reef sea spray aerosol can have a large nonvolatile organic fraction
Organic components in sea spray aerosol suppress water uptake
Polar environments are among the fastest changing regions on the planet. It is a crucial time to make significant improvements in our understanding of how ocean and ice biogeochemical processes are ...linked with the atmosphere. This is especially true over Antarctica and the Southern Ocean where observations are severely limited and the environment is far from anthropogenic influences. In this commentary, we outline major gaps in our knowledge, emerging research priorities, and upcoming opportunities and needs. We then give an overview of the large-scale measurement campaigns planned across Antarctica and the Southern Ocean in the next 5 years that will address the key issues. Until we do this, climate models will likely continue to exhibit biases in the simulated energy balance over this delicate region. Addressing these issues will require an international and interdisciplinary approach which we hope to foster and facilitate with ongoing community activities and collaborations.
Internally and externally mixed aerosols present significant challenges in assessing the hygroscopicity of each aerosol component. This study presents a new sampling technique which uses differences ...in volatility to separate mixtures and directly examine their respective composition and hygroscopic contribution. A shared thermodenuder and unheated bypass line are continuously cycled between an aerosol mass spectrometer and a volatility and hygroscopicity tandem differential mobility analyser, allowing real-time comparative analysis of heated and unheated aerosol properties. Measurements have been taken of both chamber-generated secondary organic aerosol and coastal marine aerosol at Cape Grim, Australia, to investigate system performance under diverse conditions. Despite rapidly changing aerosol properties and the need to restrict analysis to a narrow size range, the former experiment separated the hygroscopic influences of ammonium sulfate and two distinct organic components with similar oxygen to carbon ratios but different volatilities. Analysis of the marine aerosol revealed an external mixture of non-sea-salt sulfates and sea spray aerosol, which likely shared similar volatile fractions composed of sulfuric acid and a non-hygroscopic organic component.
The impacts of poor air quality on human health are becoming more apparent. Businesses and governments are implementing technologies and policies in order to improve air quality. Despite this the ...PM10 air quality in the mining town of Moranbah, Australia, has worsened since measurements commenced in 2011. The annual average PM10 concentrations during 2012, 2017, 2018 and 2019 have all exceeded the Australian National Environmental Protection Measure's standard, and there has been an increase in the frequency of exceedances of the daily standard. The average annual increase in PM10 was 1.2 ±0.5 μg m−3 per year between 2011 and 2019 and has been 2.5 ±1.2 μg m−3 per year since 2014. The cause of this has not previously been established. Here, two machine learning algorithms (gradient boosted regression and random forest) have been implemented to model and then meteorologically normalise PM10 mass concentrations measured in Moranbah. The best performing model, using the random forest algorithm, was able to explain 59% of the variance in PM10 using a range of meteorological, environmental and temporal variables as predictors. An increasing trend after normalising for these factors was found of 0.6 ± 0.5 μg m−3 per year since 2011 and 1.7 ± 0.3 μg m−3 per year since 2014. These results indicate that more than half of the increase in PM10 is due to a rise in local emissions in the region. The remainder of the rise in PM10 was found to be due to a decrease of soil water content in the surrounding region, which can facilitate higher dust emissions. Whether the presence of open-cut coal mines exacerbated the role of soil water content is unclear. Although fires can have drastic effects on the local air quality, changes in fire patterns are not responsible for the rising trend. PM10 composition measurements or more detailed data relating to local sources is still needed to better isolate these emissions. Nonetheless, this study highlights the need and potential for action by industry and government to improve the air quality and reduce health risks for the nearby population.
Display omitted
•PM10 concentrations are rising by 1.2 μg/m^3 per year in Moranbah, Australia•Machine learning methods can account for the influence of meteorology on air quality•Meteorologically normalised PM10 shows rising source emissions from mining activity and drying soil
This commentary paper from the recently formed International Global Atmospheric Chemistry (IGAC) Southern Hemisphere Working Group outlines key issues in atmospheric composition research that ...particularly impact the Southern Hemisphere. In this article, we present a broad overview of many of the challenges for understanding atmospheric chemistry in the Southern Hemisphere, before focusing in on the most significant factors that differentiate it from the Northern Hemisphere. We present sections on the importance of biogenic emissions and fires in the Southern Hemisphere, showing that these emissions often dominate over anthropogenic emissions in many regions. We then describe how these and other factors influence air quality in different parts of the Southern Hemisphere. Finally, we describe the key role of the Southern Ocean in influencing atmospheric chemistry and conclude with a description of the aims and scope of the newly formed IGAC Southern Hemisphere Working Group.
The impact of the dust sea‐surface forcing (DSSF) on the oceanic Primary Production (PP) is investigated here by using 1D modelling approach coupling an atmospheric radiative transfer model and a ...simple PP model. Simulations reveal that dust are able to induce a significant decrease of PP due to the attenuation of light by about 15–25% for dust optical depth (DOD) larger than 0.6–0.7 (at 550 nm). For DOD lower than ∼0.2–0.3, the influence of dust on PP is weak (∼5%). In addition to DOD, the important role played by dust single scattering albedo (DSSA) is also shown. Realistic applications over the Senegal coast are studied using SeaWiFS and AERONET observations. The analysis showed that PP could be reduced by about 15–20% during the spring period. This study highlights that dust/light interactions need to be parameterized in coupled ocean‐atmosphere models used to estimate PP at regional scales.
The Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role of aerosols on the regional climate of southern Africa. This is a unique environment where natural and ...anthropogenic aerosols and a semipermanent and widespread stratocumulus (Sc) cloud deck are found. The project aims to understand the dynamical, chemical, and radiative processes involved in aerosol–cloud–radiation interactions over land and ocean and under various meteorological conditions. The AEROCLO-sA field campaign was conducted in August and September of 2017 over Namibia. An aircraft equipped with active and passive remote sensors and aerosol in situ probes performed a total of 30 research flight hours. In parallel, a ground-based mobile station with state-of-the-art in situ aerosol probes and remote sensing instrumentation was implemented over coastal Namibia, and complemented by ground-based and balloonborne observations of the dynamical, thermodynamical, and physical properties of the lower troposphere. The focus laid on mineral dust emitted from salty pans and ephemeral riverbeds in northern Namibia, the advection of biomass-burning aerosol plumes from Angola subsequently transported over the Atlantic Ocean, and aerosols in the marine boundary layer at the ocean–atmosphere interface. This article presents an overview of the AEROCLO-sA field campaign with results from the airborne and surface measurements. These observations provide new knowledge of the interactions of aerosols and radiation in cloudy and clear skies in connection with the atmospheric dynamics over southern Africa. They will foster new advanced climate simulations and enhance the capability of spaceborne sensors, ultimately allowing a better prediction of future climate and weather in southern Africa.
The impacts of poor air quality on human health are becoming more apparent. Businesses and governments are implementing technologies and policies in order to improve air quality. Despite this the PM
...air quality in the mining town of Moranbah, Australia, has worsened since measurements commenced in 2011. The annual average PM
concentrations during 2012, 2017, 2018 and 2019 have all exceeded the Australian National Environmental Protection Measure's standard, and there has been an increase in the frequency of exceedances of the daily standard. The average annual increase in PM
was 1.2
0.5 μg
per year between 2011 and 2019 and has been 2.5
1.2 μg
per year since 2014. The cause of this has not previously been established. Here, two machine learning algorithms (gradient boosted regression and random forest) have been implemented to model and then meteorologically normalise PM
mass concentrations measured in Moranbah. The best performing model, using the random forest algorithm, was able to explain 59% of the variance in PM
using a range of meteorological, environmental and temporal variables as predictors. An increasing trend after normalising for these factors was found of 0.6
0.5 μg
per year since 2011 and 1.7
0.3 μg
per year since 2014. These results indicate that more than half of the increase in PM
is due to a rise in local emissions in the region. The remainder of the rise in PM
was found to be due to a decrease of soil water content in the surrounding region, which can facilitate higher dust emissions. Whether the presence of open-cut coal mines exacerbated the role of soil water content is unclear. Although fires can have drastic effects on the local air quality, changes in fire patterns are not responsible for the rising trend. PM
composition measurements or more detailed data relating to local sources is still needed to better isolate these emissions. Nonetheless, this study highlights the need and potential for action by industry and government to improve the air quality and reduce health risks for the nearby population.
PDF
