A14A-01
PANs in the North Atlantic and Arctic Oceans in Springtime 2008
PANs, (acyl peroxynitrates), are often the most abundant odd-nitrogen (NOy) species in the Northern Hemisphere low-temperature environments. As a result, PANs transport, and subsequent thermal decomposition to NO2, represent a major source of NOx to the background troposphere. Measurements of PAN and PPN were made aboard the R/V Knorr during ICEALOT (International Chemistry Experiment in the Arctic Lower Troposphere) project. The compound concentrations and their systematic dependency on air-mass origin and transport will be presented in the context of other geographical and seasonal sources of NOy to the remote atmosphere.
A14A-02
High Latitude Nitrogen Oxide oxidation during wintertime
Nitrogen oxides are key chemicals in the atmosphere that affect ozone levels and eventually are oxidized to
nitric acid, leading to acidification and fertilization where they are deposited. During high-latitude wintertime
conditions, photochemical removal pathways slow due to lack of sunlight and ozone oxidizes NO2 to
NO3, which reacts with NO2 to form dinitrogen pentoxide (N2O5) that then hydrolyses to nitric
acid on water-containing surfaces. Modeling studies indicate that this "dark" pathway is responsible for the
majority of nitrogen oxide removal at high latitudes during winter. However, little is known about the surfaces
on which the hydrolysis takes place and how ambient conditions affect this pathway. In a series of field
campaigns, our group has measured ambient mixing ratios of N2O5 and its precursors and sinks so
as to understand nighttime nitrogen oxide removal under high latitude conditions. We find that airmasses
saturated with respect to ice have significantly shorter N2O5 lifetimes than sub-saturated airmasses,
indicating a significant role for ice surfaces in the dark oxidation pathway. Airmasses that are saturated with
respect to ice may contain small ice particles that act as heterogeneous reaction sites or saturation with
respect to ice could result from airmass contact with the snowpack, indicating N2O5 is deposited to
the snow surface. In this presentation, we discuss these possible losses and implications for chemistry in
high-latitude pollution plumes.
http://www.uaf.edu/chem/simpson
A14A-03
Volatile Organic Compounds (VOCs) Measured in the Arctic Aboard the R/V Knorr During ICEALOT 2008: Primary Sources and Evidence of Halogen Oxidation
A full suite of gas-phase compounds were measured in-situ aboard the R/V Knorr as part of the International Chemistry Experiment in the Arctic Lower Troposphere (ICEALOT) conducted in March and April of 2008. A wide range of VOCs were measured by a two-channel GC-MS (Gas Chromatograph-Mass Spectrometer) every 30 minutes significantly expanding the spatial and temporal database of these compounds in the Arctic spring-time marine boundary layer. This was done in order to (1) characterize the composition of VOCs over the ice-free regions of the Arctic and to (2) determine the relative impacts of local VOC sources (i.e. oceanic and local point sources) and sinks (i.e. halogen oxidation) in this isolated region. The VOC composition was dominated by relatively long-lived VOCs, such as ethane (median = 2.1 ppbv) and propane (median = 1.3 ppbv), and remained relatively constant throughout the far North Atlantic; however, there were distinct events that displayed significant variability in the measured mixing ratios of some VOCs. One episode is characterized by a 2-10 fold increase in C2-C6 alkanes indicating a primary source of anthropogenic emissions near the Kola Peninsula (Russia). In contrast, a significant decline in certain VOCs is associated with a halogen oxidation episode that occurred during an ozone depletion event (ODE). Halogen oxidation was further evidenced by sharp departures in the [benzene]/[acetylene] and [iso-butane]/[n-butane] ratios which are known to be affected by halogen chemistry.
A14A-04
Shipboard measurement of ozone depletion events in the Arctic Ocean during ICEALOT 2008
During the International Chemistry Experiment in the Arctic Lower Troposphere (ICEALOT) 2008, distinct ozone depletion events (ODEs) were observed aboard the R/V Knorr over a three-day period (April 15 to 17) near the Svalbard archipelago in the Arctic Ocean. Rapid changes in ozone mixing ratio were observed (up to 20 ppbv/hr) and absolute mixing ratios as low as 1 ppbv were measured. These ODEs were only observed in the northernmost (>77 °N) and coldest (<-10 °C) areas. Comparison to measurements of long-lived atmospheric compounds (e.g. carbon monoxide) gives evidence to transport versus in-place chemical production of the ODEs. Volatile organic compounds (VOCs) and photolysis rate measurements made during the cruise provide a means to estimate concentrations of the atmospheric oxidants hydroxyl radical (OH), atomic chlorine (Cl) and atomic bromine (Br). Coincident to the largest ODE, a significant (>10 nM) concentration of oceanic dimethyl sulfide (DMS) was observed. The effect of the estimated oxidant mixing ratios on DMS atmospheric lifetime will be discussed.
A14A-05
Light absorption by aerosols in the European Arctic: First results from ICEALOT
Measurements of light absorption by atmospheric aerosols in the Arctic marine boundary were made aboard the R/V Knorr during the springtime (March/April) ICEALOT campaign. The absorption measurements were made using a photoacoustic spectrometer operating at 532 nm and a particle soot absorption photometer operating at 467 nm, 530 nm and 660 nm. These measurements were made along with light extinction measurements at 532 nm to allow for accurate determination of the particle single scatter albedo, SSA. The absorption levels were < 0.5 Mm-1 for most of the campaign, with typical SSA values > 0.93. A few "plumes", originating from Eurasia, were encountered where the observed absorption was significantly higher than background (~ 2 Mm-1) and the SSA was lower, although the observed SSA varied between the different plumes despite the similar absorption levels. We will discuss the absolute absorption levels and the variability in the SSA observed throughout the campaign in terms of the concurrent physical and chemical properties of the aerosol, the aerosol age and the specific source region. We will combine these in situ measurements made in the marine boundary layer with clear sky optical depth measurements to make estimates of the local direct radiative forcing by the aerosol, with a special focus on measurements made near the sea-ice edge in the Greenland Sea.
A14A-06
The Composition of Individual Aerosol Particles over the North Slope of Alaska during ISDAC
During the month of April 2008 a single particle mass spectrometer, SPLAT II, was deployed on board the Canadian National Research Council Convair 580 aircraft for participation in the Indirect and Semi-Direct Aerosol Campaign (ISDAC). ISDAC's main scientific objective was to improve our understanding of the relationship between the properties of aerosol particles over the North Pole and their impact on the regional climate. During ISDAC SPLAT II participated in all 27 flights that lasted slightly over 100 hrs. It measured the size of more than 10 million particles and characterized the composition of over 3 million of them. When sampling in clear air SPLAT II measured a wide range of particle compositions, including sulfates mixed with organics, nitrates mixed with organic, processed and freshly emitted sea-salt, a few dust particles, and a significant number of biomass burning particles. Many of these particle types appeared in aerosol layers that had horizontal and vertical filamentous structures. Biomass burning particles, many of which were transported from Asia, were rather prevalent over the North Slope of Alaska during the campaign. Since one of the main goals of this campaign was to characterize cloud properties, large fraction of the data was collected through the CVI inlet. The ice-clouds sampled in ISDAC had typically very low ice crystal concentrations; correspondingly, when sampled through the CVI inlet the number of characterized particles drops precipitously. Despite the low number concentrations SPLAT was able to measure the size and composition of thousands of ice-nuclei. Since the CVI inlet transmits, in addition to ice crystals, liquid droplets, SPLAT was able to characterize a large number of particles that served as cloud condensation nuclei as well. We will present a preliminary analysis of the single particle data collected during this campaign.
A14A-07
Airborne Photoacoustic Observations of Aerosol Optical Properties Aloft Alaska: Quantifying Aerosol Radiative Forcing in the Arctic
Los Alamos deployed the world's first 3-laser aerosol photoacoustic and nephelopmeter instrument on a
Canadian Convair-580 aircraft in April 2008 for DOE's Indirect and Semidirect Effects of Aerosols (ISDAC)
campaign (www.arm.gov). Our instrument measured aerosol absorption, scattering and single scattering
albedo at 405, 532, and 781 nm. There were 42 complementary measurements of cloud microphysics,
aerosol chemistry, and ice composition. On numerous flights we intercepted and interrogated pervasive
pollution layers aloft Alaska. The absorption and scattering signals occurred in layers from 1 to 6 km above
the surface and approached 200 to 30 (Mm)-1 respectively. Alternating light and dark aerosol layers
with single scatter albedo ranging from 0.7 to 0.95 were evident, and they extended over vast areas. Real
time satellite data assimilated transport models indicate that this pollution was imported from Chinese dust
storms and Siberian fires as well as from Eurasian energy sectors. Our wavelength dependent optical
properties are used to diagnose the soot, dust, sulfate and organic components of this complex soup of
pollutants. We are testing the fidelity of our diagnostics by analyzing chemical compositions from a single
particle laser ablation spectrometer instrument developed by Pacific Northwest National Laboratory. We use
our optical observations to estimate a direct radiative forcing by pollution of the order of 10 to 30 of W m-
2. This forcing by aerosols is much larger than that by greenhouse gases. Our results underscore the
need to accurately treat long range pollution transport in models to simulate the observed rapid melting of
the Arctic ice sheet.
http://aerosols.lanl.gov/
A14A-08
The Role of Aerosol Pollution in Warming the Arctic Surface via Radiative-Dynamic Feedbacks in Clouds
It has recently been shown that pollution with mid-latitude origins might be warming the Arctic surface through increases in the longwave emissivity of clouds. Introducing aerosol pollution, which act as cloud condensation nuclei, into a cloud increases the number of cloud droplets while causing each droplet to be smaller. This changes emissivity of the cloud resulting in an increase in thermal emission. Increasing thermal emission produces more cloud-top cooling, creating a temperature contrast. A temperature contrast drives motion in the cloud and is a feedback on the motion that initiated the cloud. Using the University of Utah Large Eddy Simulation Model, with idealized microphysics, but coupled radiation and dynamics, we create stratus from a moist boundary layer. Our simulations suggest that in a polluted environment, aerosol pollution enhances cloud-top radiative cooling in thin stratus by making a cloud more thermally opaque. Compared to a clean cloud, the increased cooling makes dynamic motions more vigorous and the stratus layer deepen more rapidly: effectively the cloud evolution is accelerated. The combined effect of emissivity perturbations and radiatively induced feedbacks is to substantially amplify the effect of aerosol pollution on cloudy thermal emission and Arctic surface warming.