Abstract
Benzene, toluene, ethylbenzene and xylenes can contribute to hydroxyl reactivity and secondary aerosol formation in the atmosphere. These aromatic hydrocarbons are typically classified as ...anthropogenic air pollutants, but there is growing evidence of biogenic sources, such as emissions from plants and phytoplankton. Here we use a series of shipborne measurements of the remote marine atmosphere, seawater mesocosm incubation experiments and phytoplankton laboratory cultures to investigate potential marine biogenic sources of these compounds in the oceanic atmosphere. Laboratory culture experiments confirmed marine phytoplankton are a source of benzene, toluene, ethylbenzene, xylenes and in mesocosm experiments their sea-air fluxes varied between seawater samples containing differing phytoplankton communities. These fluxes were of a similar magnitude or greater than the fluxes of dimethyl sulfide, which is considered to be the key reactive organic species in the marine atmosphere. Benzene, toluene, ethylbenzene, xylenes fluxes were observed to increase under elevated headspace ozone concentration in the mesocosm incubation experiments, indicating that phytoplankton produce these compounds in response to oxidative stress. Our findings suggest that biogenic sources of these gases may be sufficiently strong to influence atmospheric chemistry in some remote ocean regions.
We present findings from the Measurements of Urban, Marine and Biogenic Air (MUMBA) campaign, which took place in the coastal city of Wollongong in New South Wales, Australia. We focus on a few key ...air quality indicators, along with a comparison to regional scale chemical transport model predictions at a spatial resolution of 1 km by 1 km. We find that the CSIRO chemical transport model provides accurate simulations of ozone concentrations at most times, but underestimates the ozone enhancements that occur during extreme temperature events. The model also meets previously published performance standards for fine particulate matter less than 2.5 microns in diameter (PM2.5), and the larger aerosol fraction (PM10). We explore the observed composition of the atmosphere within this urban air-shed during the MUMBA campaign and discuss the different influences on air quality in the city. Our findings suggest that further improvements to our ability to simulate air quality in this coastal city can be made through more accurate anthropogenic and biogenic emissions inventories and better understanding of the impact of extreme temperatures on air quality. The challenges in modelling air quality within the urban air-shed of Wollongong, including difficulties in accurate simulation of the local meteorology, are likely to be replicated in many other coastal cities in the Southern Hemisphere.
Oceans cover over
70 % of the Earth's surface. Ship-based measurements are an important
component in developing an understanding of atmosphere of this vast region. A
common problem that impacts the ...quality of atmospheric data collected from
marine research vessels is exhaust from both diesel combustion and waste
incineration from the ship itself. Described here is an algorithm, developed
for the recently commissioned Australian blue-water research vessel (RV)
Investigator, that identifies exhaust periods in sampled air. The RV
Investigator, with two dedicated atmospheric laboratories,
represents an unprecedented opportunity for high-quality measurements of the
marine atmosphere. The algorithm avoids using ancillary data such as wind
speed and direction, and instead utilises components of the exhaust itself –
aerosol number concentration, black carbon concentration, and carbon monoxide
and carbon dioxide mixing ratios. The exhaust signal is identified within
each of these parameters individually before they are combined and an
additional window filter is applied. The algorithm relies heavily on
statistical methods, rather than setting thresholds that are too rigid to
accommodate potential temporal changes. The algorithm is more effective than
traditional wind-based filters in removing exhaust data without removing
exhaust-free data, which commonly occurs with traditional filters. In
application to the current dataset, the algorithm identifies 26 % of the
wind filter's “clean” data as exhaust, and recovers 5 % of data falsely
removed by the wind filter. With suitable testing, the algorithm has the
potential to be applied to other ship-based atmospheric measurements where
suitable measurements exist.
The capture vaporizer (CV) was developed to reduce uncertainties in non-refractory aerosol composition measurements made using the aerosol mass spectrometer (AMS) and the aerosol chemical speciation ...monitor (ACSM). Use of the capture vaporizer has achieved this by improving the instruments' collection efficiency to ∼1, but it has also lengthened the aerosol particles' residence times in the instrument, which has changed AMS and ACSM measurements using the standard vaporizer by altering known fragmentation patterns of organic marker species and increasing the likelihood of detecting refractory particles such as sea salt at typical operating temperatures (550 C). This study reports that the changes affected by the capture vaporizer leads to sea salt particles interfering with measurements of biomass burning organic aerosols (BBOA) in environments where both particle sources are present as the ACSM's unit mass resolution is unable to distinguish between different molecules with the same molecular mass. Demonstration of this interference was performed using CV-Time of Flight-ACSM (CV-ToF-ACSM) measurements at two coastal Australian locations: the Kennaook-Cape Grim Baseline Air Pollution Station, Tasmania; and the site of the COALA-2020 (Characterizing Organics and Aerosol Loading over Australia 2020) campaign in New South Wales. Concentrations of BBOA marker ions
m
/
z
60 and
m
/
z
73 were examined at both locations, which showed two distinct branches of points: one where the two marker ions were positively correlated and one that was uncorrelated. This was due to
m
/
z
60 also being a marker for sea salt. A threshold concentration of
m
/
z
73 was established at each location to recognise periods where
m
/
z
60 originated from BBOA. Lower concentrations of
m
/
z
44 and radon when
m
/
z
73 concentration was below the BBOA threshold indicated that
m
/
z
60 concentration during these periods corresponded to inorganic particles of marine origin. Positive Matrix Factorization has also been shown to separate
m
/
z
60 concentration from the two sources. This study suggests that using CV-ToF-ACSMs in coastal locations that are exposed to biomass burning smoke needs to consider sea salt interference when identifying BBOA.
Measurements of biomass burning organic aerosols using the capture vaporizer-ACSM are interfered with by sea salt aerosols, as both have
m
/
z
60 as a marker ion and the capture vaporizer is able to detect refractory particles like sea salt.
Abstract The goal of the Sea2Cloud project is to study the interplay between surface ocean biogeochemical and physical properties, fluxes to the atmosphere, and ultimately their impact on cloud ...formation under minimal direct anthropogenic influence. Here we present an interdisciplinary approach, combining atmospheric physics and chemistry with marine biogeochemistry, during a voyage between 41° and 47°S in March 2020. In parallel to ambient measurements of atmospheric composition and seawater biogeochemical properties, we describe semicontrolled experiments to characterize nascent sea spray properties and nucleation from gas-phase biogenic emissions. The experimental framework for studying the impact of the predicted evolution of ozone concentration in the Southern Hemisphere is also detailed. After describing the experimental strategy, we present the oceanic and meteorological context including provisional results on atmospheric thermodynamics, composition, and flux measurements. In situ measurements and flux studies were carried out on different biological communities by sampling surface seawater from subantarctic, subtropical, and frontal water masses. Air–Sea-Interface Tanks (ASIT) were used to quantify biogenic emissions of trace gases under realistic environmental conditions, with nucleation observed in association with biogenic seawater emissions. Sea spray continuously generated produced sea spray fluxes of 34% of organic matter by mass, of which 4% particles had fluorescent properties, and which size distribution resembled the one found in clean sectors of the Southern Ocean. The goal of Sea2Cloud is to generate realistic parameterizations of emission flux dependences of trace gases and nucleation precursors, sea spray, cloud condensation nuclei, and ice nuclei using seawater biogeochemistry, for implementation in regional atmospheric models.
The Sydney Particle Study involved the comprehensive measurement of
meteorology, particles and gases at a location in western Sydney during
February–March 2011 and April–May 2012. The aim of this ...study was to
increase scientific understanding of particle formation and transformations
in the Sydney airshed. In this paper we describe the methods used to collect
and analyse particle and gaseous samples, as well as the methods employed
for the continuous measurement of particle concentrations, particle
microphysical properties, and gaseous concentrations. This paper also
provides a description of the data collected and is a metadata record for
the data sets published in Keywood et al. (2016a,
https://doi.org/10.4225/08/57903B83D6A5D) and Keywood et al. (2016b,
https://doi.org/10.4225/08/5791B5528BD63).
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