14 research outputs found
Aerosol Optical Hygroscopicity Measurements during the 2010 CARES Campaign
Measurements of the effect of water uptake on particulate light extinction or scattering made at two locations during the 2010 CARES study around Sacramento, CA are reported. The observed influence of water uptake, characterized through the dimensionless optical hygroscopicity parameter γ, is compared with calculations constrained by observed particle size distributions and size-dependent particle composition. A closure assessment has been carried out that allowed for determination of the average hygroscopic growth factors (GF) at 85% relative humidity and the dimensionless hygroscopicity parameter κ for oxygenated organic aerosol (OA) and for supermicron particles, yielding κ = 0.1–0.15 and 0.9–1.0, respectively. The derived range of oxygenated OA κ values are in line with previous observations. The relatively large values for supermicron particles is consistent with substantial contributions of sea salt-containing particles in this size range. Analysis of time-dependent variations in the supermicron particle hygroscopicity suggest that atmospheric processing, specifically chloride displacement by nitrate and the accumulation of secondary organics on supermicron particles, can lead to substantial depression of the observed GF
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Contributions of transported Prudhoe Bay oil field emissions to the aerosol population in Utqiaġvik, Alaska
Loss of sea ice is opening the Arctic to increasing development involving oil and gas extraction and shipping. Given the significant impacts of absorbing aerosol and secondary aerosol precursors emitted within the rapidly warming Arctic region, it is necessary to characterize local anthropogenic aerosol sources and compare to natural conditions. From August to September 2015 in Utqiaġvik (Barrow), AK, the chemical composition of individual atmospheric particles was measured by computer-controlled scanning electron microscopy with energy-dispersive X-ray spectroscopy (0.13-4 μm projected area diameter) and real-time single-particle mass spectrometry (0.2-1.5 μm vacuum aerodynamic diameter). During periods influenced by the Arctic Ocean (70 % of the study), our results show that fresh sea spray aerosol contributed ∼ 20 %, by number, of particles between 0.13 and 0.4 μm, 40-70 % between 0.4 and 1 μm, and 80-100 % between 1 and 4 μm particles. In contrast, for periods influenced by emissions from Prudhoe Bay (10 % of the study), the third largest oil field in North America, there was a strong influence from submicron (0.13-1 μm) combustion-derived particles (20-50 % organic carbon, by number; 5-10 % soot by number). While sea spray aerosol still comprised a large fraction of particles (90 % by number from 1 to 4 μm) detected under Prudhoe Bay influence, these particles were internally mixed with sulfate and nitrate indicative of aging processes during transport. In addition, the overall mode of the particle size number distribution shifted from 76 nm during Arctic Ocean influence to 27 nm during Prudhoe Bay influence, with particle concentrations increasing from 130 to 920 cm-3 due to transported particle emissions from the oil fields. The increased contributions of carbonaceous combustion products and partially aged sea spray aerosol should be considered in future Arctic atmospheric composition and climate simulations
OH-Initiated Heterogeneous Oxidation of Internally-Mixed Squalane and Secondary Organic Aerosol
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OH-Initiated Heterogeneous Oxidation of Internally-Mixed Squalane and Secondary Organic Aerosol
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Heating-Induced Evaporation of Nine Different Secondary Organic Aerosol Types.
The volatility of the compounds comprising organic aerosol (OA) determines their distribution between the gas and particle phases. However, there is a disconnect between volatility distributions as typically derived from secondary OA (SOA) growth experiments and the effective particle volatility as probed in evaporation experiments. Specifically, the evaporation experiments indicate an overall much less volatile SOA. This raises questions regarding the use of traditional volatility distributions in the simulation and prediction of atmospheric SOA concentrations. Here, we present results from measurements of thermally induced evaporation of SOA for nine different SOA types (i.e., distinct volatile organic compound and oxidant pairs) encompassing both anthropogenic and biogenic compounds and O3 and OH to examine the extent to which the low effective volatility of SOA is a general phenomenon or specific to a subset of SOA types. The observed extents of evaporation with temperature were similar for all the SOA types and indicative of a low effective volatility. Furthermore, minimal variations in the composition of all the SOA types upon heating-induced evaporation were observed. These results suggest that oligomer decomposition likely plays a major role in controlling SOA evaporation, and since the SOA formation time scale in these measurements was less than a minute, the oligomer-forming reactions must be similarly rapid. Overall, these results emphasize the importance of accounting for the role of condensed phase reactions in altering the composition of SOA when assessing particle volatility
Heating-Induced Evaporation of Nine Different Secondary Organic Aerosol Types
The volatility of the compounds comprising
organic aerosol (OA)
determines their distribution between the gas and particle phases.
However, there is a disconnect between volatility distributions as
typically derived from secondary OA (SOA) growth experiments and the
effective particle volatility as probed in evaporation experiments.
Specifically, the evaporation experiments indicate an overall much
less volatile SOA. This raises questions regarding the use of traditional
volatility distributions in the simulation and prediction of atmospheric
SOA concentrations. Here, we present results from measurements of
thermally induced evaporation of SOA for nine different SOA types
(i.e., distinct volatile organic compound and oxidant pairs) encompassing
both anthropogenic and biogenic compounds and O<sub>3</sub> and OH
to examine the extent to which the low effective volatility of SOA
is a general phenomenon or specific to a subset of SOA types. The
observed extents of evaporation with temperature were similar for
all the SOA types and indicative of a low effective volatility. Furthermore,
minimal variations in the composition of all the SOA types upon heating-induced
evaporation were observed. These results suggest that oligomer decomposition
likely plays a major role in controlling SOA evaporation, and since
the SOA formation time scale in these measurements was less than a
minute, the oligomer-forming reactions must be similarly rapid. Overall,
these results emphasize the importance of accounting for the role
of condensed phase reactions in altering the composition of SOA when
assessing particle volatility
OH-Initiated Heterogeneous Oxidation of Internally-Mixed Squalane and Secondary Organic Aerosol
Recent work has established that
secondary organic aerosol (SOA)
can exist as an amorphous solid, leading to various suggestions that
the addition of SOA coatings to existing particles will decrease the
reactivity of those particles toward common atmospheric oxidants.
Experimental evidence suggests that O<sub>3</sub> is unable to physically
diffuse through an exterior semisolid or solid layer thus inhibiting
reaction with the core. The extent to which this suppression in reactivity
occurs for OH has not been established, nor has this been demonstrated
specifically for SOA. Here, measurements of the influence of adding
a coating of α-pinene+O<sub>3</sub> SOA onto squalane particles
on the OH-initiated heterogeneous oxidation rate are reported. The
chemical composition of the oxidized internally mixed particles was
monitored online using a vacuum ultraviolet-aerosol mass spectrometer.
Variations in the squalane oxidation rate with particle composition
were quantified by measurement of the effective uptake coefficient,
γ<sub>eff</sub>, which is the loss rate of a species relative
to the oxidant-particle collision rate. Instead of decreasing, the
measured γ<sub>eff</sub> increased continuously as the SOA coating
thickness increased, by a factor of ∼2 for a SOA coating thickness
of 42 nm (corresponding to ca. two-thirds of the particle mass). These
results indicate that heterogeneous oxidation of ambient aerosol by
OH radicals is not inhibited by SOA coatings, and further that condensed
phase chemical pathways and rates in organic particles depend importantly
on composition
Contributions of Transported Prudhoe Bay Oilfield Emissions to the Aerosol Population in Utqiaġvik, Alaska
Loss of sea ice is opening the Arctic to increasing development involving oil and gas extraction and shipping. Given the significant impacts of absorbing aerosol and secondary aerosol precursors emitted within the rapidly warming Arctic region, it is necessary to characterize local anthropogenic aerosol sources and compare to natural conditions. From August to September 2015 in Utqiaġvik (Barrow), AK, the chemical composition of individual atmospheric particles was measured by computer-controlled scanning electron microscopy with energy-dispersive X-ray spectroscopy (0.13-4 μm projected area diameter) and real-time single-particle mass spectrometry (0.2-1.5 μm vacuum aerodynamic diameter). During periods influenced by the Arctic Ocean (70 % of the study), our results show that fresh sea spray aerosol contributed ∼ 20 %, by number, of particles between 0.13 and 0.4 μm, 40-70 % between 0.4 and 1 μm, and 80-100 % between 1 and 4 μm particles. In contrast, for periods influenced by emissions from Prudhoe Bay (10 % of the study), the third largest oil field in North America, there was a strong influence from submicron (0.13-1 μm) combustion-derived particles (20-50 % organic carbon, by number; 5-10 % soot by number). While sea spray aerosol still comprised a large fraction of particles (90 % by number from 1 to 4 μm) detected under Prudhoe Bay influence, these particles were internally mixed with sulfate and nitrate indicative of aging processes during transport. In addition, the overall mode of the particle size number distribution shifted from 76 nm during Arctic Ocean influence to 27 nm during Prudhoe Bay influence, with particle concentrations increasing from 130 to 920 cm-3 due to transported particle emissions from the oil fields. The increased contributions of carbonaceous combustion products and partially aged sea spray aerosol should be considered in future Arctic atmospheric composition and climate simulations