November 18-19, 1999; C4, La Jolla
The first meeting of the INDOEX Harmony Workshop was well attended with representatives of most platforms and aerosol measurements present (see below). Information on the details of the meeting and basic objectives can be found on the PMEL Website -- http://saga.pmel.noaa.gov/indoex/harmony/. These include comparison periods for each platform selected and stratified according to scattering values and prevailing winds or trajectories. This report is an interim assessment that is being released before the fall AGU, 1999 so that the INDOEX community might benefit from these initial findings.
It is important to recognize that the Harmony Workshop was a first step in bringing diverse measurements and platforms together in order to gauge INDOEX success in constraining aerosol physics, chemistry and optics. On the first day, three groups provided brief summaries of available data and then met as separate groups with their co-ordinators to evaluate Chemical Measurements (P. Quinn), Optical Measurements (J. Ogren) and Size Distribution Measurements (A. Clarke). A brief synopsis of preliminary group findings can be found below.
The second day groups met together and opportunities for assessing the links between measurements were explored. Since side by side comparison of the platforms were rare, efforts were made to identify features (Common Products: - such as ratios of measurements – scattering to mass (Dp<1 µm), single scatter albedo, BC/OC/TC, BC/SO4 , single scatter albedo, coarse to fine mass etc.) with the notion that these properties should be common to most platforms under similar aerosol conditions (provided sampling characteristics were similar). Progress was made in several areas but, given the limited time for such comparisons, it is important that these efforts be continued between investigators. Towards this end a variety of ONE ON ONE comparison topics were identified and names were attached to them for carrying out these studies. These are listed below and will be added to the website where progress will be posted. It is expected that others not at the workshop may wish to join some of these efforts or may have other specific Harmony comparisons they are working on. If you are one of those, you are encouraged to contact and work with those identified on the list below or to suggest another topic of your own. These comparisons are important to the use of the INDOEX data set and it is hoped that prompt attention to these efforts will result in a brief report submitted to update our understanding. These reports will be added to the website when available.
INTERIM SUMMARY REPORTS
Shapes of most distributions agree well for max/min half widths and peak position except for C-130 wing probes.Supermicometer:
Mass mean "dry" geometric Dp varies between 0.3 and 0.4 µm for following instruments:
DMA on RB (Bates, Ift)
DMA + OPC on C-130 (Clarke)
DMA on KCO (Cantrell)
Moudi Impactor on KCO (Cass) after correcting for "wet" collection and aerodynamic size.
Preliminary indication that RB DMA concentration (not shape) may be low by about 30% is being investigated.
C-130 Wing probe data appears to show significant undercounting in the 0.2-0.4 µm size range
KCO – no data on hand yetScatter/Mass comparisons (Submicrometer)
RB – APS shows peak near 3 µm is common – (sea-salt generally)
C-130 – Wing probe shows one volume peak variable near 2 µm and sometimes a peak near 10 µm ( not able to be measured by other instruments). (needs more work)
C-130 – OPC peak near 3m m but not pronounced. Expect this is reduced by a factor of 3 or more due to inlet losses. Needs more work.
KCO – 8 gravimetric measurements of samples from Moudi Impactor ranged from 2.5-6.0 m2 gm-1 with average of 3.28 m2 gm-1 for scattering at 40% (Cass).
C-130 – 20 Measurements with OPC (at 30m alt.) and at about 40%RH. Values ranged 2.0-5.0 m2gm-1 with average 3.07 m2gm-1; density assumed 1.7gm m-3.
C-130 - A. Andreae obtained most values near 6-8 m2gm-1 but does not include unanalyzed species.
RB – 22 measurements of gravimetric mass and the scattering coefficient at 55% RH resulted in a range of 3.8 to 6.5 m2 gm-1 and an average of 4.7 m2 gm-1 (Quinn).
Fine aerosol chemical composition was compared for measurements from the C130 (stacked filter units, size cut of 1 – 2 mm at RH of airplane inlet), KCO (Moudi, D < 1 µm and D < 1.8 µm, bulk filter D < 2.5 mm, and Sierra, D < 1.14 µm, all collecting aerosol at ambient RH), and the Ron Brown (Berner, D < 0.5 and D < 1.0 µm at 55% RH). All size cuts are given in aerodynamic diameter. The number concentration of aerosol particles containing specific chemical components, as derived from the ATOFMS measurements, was also compared for the 0.2 to 1.0 and 1.0 to 2.5 µm size ranges.
These comparisons are preliminary as no uncertainties or standard deviations were taken into account. In addition, for some species only a subset of the samples from a given platform have been analyzed. Therefore, future work includes listing uncertainties and/or standard deviations and adding all analyzed samples to the comparison.
1. Fine sulfate
Agreement between platforms is within uncertainty of size cuts and natural variability although the KCO bulk filter (D < 2.5 µm) gives higher values suggesting an influence of coarse aerosol not observed in the samplers with a lower size cut.
Low scattering regime: Concentrations range from a low of 0.6 µg
m-3 for the Southern Indian Ocean to 3 µg m-3
for trajectories from the Arabian Sea. The Southern Indian Ocean values
are near Pacific marine boundary layer concentrations.
Medium scattering regime: Concentrations range from 2 to 6 µg m-3.
High scattering regime: Concentrations range from 4 to 13 µg m-3. Highest values are similar to those measured over the NE United States.
For all scattering regimes, number concentrations from the ATOFMS confirm
that the majority of sulfate is found in the submicron size range.
2. Fine potassium (water soluble for all measurements except the ATOFMS) – a tracer of combustion.
At this point, measurements are available from the C130 and the Ron Brown. Agreement between these two platforms is good and certainly within the uncertainty of the measurements.
Low scattering regime: Concentrations range from 0.003 over the Southern
Indian Ocean to 0.07 in trajectories coming from the Bay of Bengal.
Medium scattering regime: Concentrations range from 0.04 (BoBNE) to 0.4 (BoBE).
High scattering regime: Concentrations range from 0.2 to 0.5 and are equally high for BoBNE, BoBE, and AS trajectories.
Both the Berner and the ATOFMS measurements indicate that for the non-Southern
Indian Ocean air masses, K+ in the submicron size range has
a non-sea salt, combustion source.
3. Fine sodium – a tracer of sea salt.
Values are available from the C130, the KCO Sierra, and the Ron Brown
Berner. C130 values range from 0.02 to 0.35, Sierra from 0.07 to 0.14,
and Berner from 0.05 to 0.08 mg m-3.
The higher values from the C130 and the KCO Sierra are most likely a result
of a wider size cut and the inclusion of coarse mode sea salt in the submicron
4. Fine NH4/SO4= molar ratio
Southern Indian Ocean ratios were lowest indicating a lack of gas phase ammonia available for sulfate neutralization and ratios from Arabian Sea trajectories were highest. Based on a comparison of Berner < 0.5 µm and < 1.0 µm values, the NH4+ is confined to particles less than 0.5 µm in diameter.
C130 and KCO Sierra values were slightly higher than KCO Moudi and Ron
Brown Berner values.
5. Fine aerosol mass.
Gravimetrically determined values from KCO Moudis and Ron Brown Berners and the sum of analyzed chemical components from the C130 and KCO Sierra were compared. A lack of a statistically significant number of samples makes a rigorous comparison difficult. The preliminary results, however, indicate that, for each of the scattering regimes, values from all platforms agreed within uncertainties and natural variability.
Low scattering regime: Concentrations are around 1 µg m-3
for the Southern and Northern Indian Oceans, 6 µg m-3
for the Bay of Bengal trajectories, and 1.4 µg m-3 for
the Arabian Sea trajectories. The Southern and Northern Indian Ocean values
are similar to those reported for the Pacific.
Medium scattering regime: 10 to 16 µg m-3 for the Bay of Bengal and Arabian Sea trajectories.
High scattering regime: 12 to 21 µg m-3 for the Bay of Bengal and Arabian Sea trajectories. These values are similar to those found over the NE United States (low end) and Los Angeles (high end).
6. Fine total and black carbon
Values are available from the C130, the KCO Moudi, the Ron Brown Berner and, for total carbon, from the ATOFMS. Many samples still have to be analyzed so these results are preliminary.
Agreement between platforms for both total and black carbon is very good (within a few percent) but the comparison must be repeated once all data are available. In addition, a comparison of black carbon concentrations with measured absorption coefficients is yet to be done.
Low scattering regime: Total carbon concentrations are around 1 µg
m-3 and black carbon is about half of that.
Medium scattering regime: Total carbon ranges from 1 to 2 µg m-3 and black carbon 0.4 to 1 µg m-3.
High scattering regime: Total carbon ranges from 3 to 9 µg m-3 and black carbon 2 to 3 µg m-3.
The ATOFMS measurements indicate that the majority of the carbon (by
number) is in the submicron size range.
7. Fine BC/TC and BC/SO4 ratios.
The BC/TC ratio showed no trend with scattering level but this could be a function of too few samples for an accurate representation of the INDOEX aerosol. Values ranged from 0.24 to 0.7 and appeared to be more variable on the C130 (0.24 to 0.45) than at KCO (0.6) or the Ron Brown (0.62 – 0.67). The ACE 2 shipboard average value was 0.35.
The BC/SO4 ratio was variable across air masses and platforms
(0.14 to 0.84). More data are needed and will become available as samples
are analyzed. At this point, the ratio is uniformly higher than the ACE
2 average value of 0.09.
C. Optical Properties
Aerosol light scattering and absorption coefficients were measured on the C-130, Ron Brown, Sagar Kanya, and at KCO. Independent systems for measuring light scattering and absorption were operated in parallel at KCO during the IFP by the University of Miami and NOAA/CMDL. Side-by-side comparisons of about 24 hours duration are available between the Ron Brown and KCO, and between the Ron Brown and Sagar Kanya. The C-130 performed ten fly-bys past KCO, and one past the Ron Brown. Representatives from all these platforms attended the workshop. Initial comparisons showed agreement among the light absorption measurements to within about 20% for all the comparisons. Similar agreement was obtained for all the light scattering measurements, with one exception: light scattering coefficients on the Ron Brown were about 70% higher than the values measured at KCO during the 24-hour comparison. The cause of this discrepancy is not yet known.
The chemical size distributions measured at KCO by the Caltech group were used to calculate aerosol light scattering coefficients, as a function of wavelength and relative humidity, as well as the aerosol light absorption coefficient. The initial results were very promising, with agreements generally within 10-20% for all three wavelengths (450, 550, 700 nm) and for relative humidities in the range 40-90%
Preliminary comparisons of the optical depth measured by the shadowband radiometers on the C-130 were made with vertical profiles of light scattering and absorption coefficients measured on the same platform, for two cases. Layer-averages of light scattering and absorption coefficients were visually determined from printed graphs, and rough adjustments for relative humidity and wavelength differences between the two measurement approaches were applied. The results of these crude comparisons were very encouraging, with agreement to within about 10%.
ONE ON ONE Harmony Comparison Efforts:
C-130 = NCAR Aircraft; RB = Ron Brown; KCO = Kaashidhoo; SK= Sagar Kanya
Howell/ Cantrell: C-130 and KCO DMA Size Distribution data
Bates/ Cantrell: RB and KCO DMPS Size data
Guazzoti/Cantrell: OPC Size Comparison RB/KCO
Quinn/Jayaraman: RB/ SK light scattering and absorption comparison.
Ogren/Kirschtetter: Light Absorption and BC on C-130
Quinn: Light Absorption and BC on RB
Howell/Andreae Chemical mass and OPC volume closure on C-130
Howell/Anderson/Kirschtetter/Ogren: Composition, Size vs. OPC and BC on C-130
Guazzotti/Anderson: Chemical composition by Size – ATOMS and E-microscopy
Ogren/Quinn: RB vs C-130, Sing. Scatt. Albedo, f, Angstrom, Angstrom vs. f
Maring/Ogren: KCO scattering and absorption harmony
Clarke/ Howell and all: Collect and compare mass scattering efficiencies
Bates/Quinn/Ogren: KCO/RB nephelometer side by side comparison issue
Coffee/Howell/Cantrell: KCO/C-130 OPC data comparison
Cass/Quinn: Compare f(RH) approaches (density too?)
Novakov/Andreae/Cachier/Neuss BC/OC/TC comparison
Ogren/Howell: Summary of KCO and C-130 appropriate comparison times
Gandrud/Guazzotti/Cass: Wing Probe C-130 and KCO OPC data – supermicron
Cass/Prather: Mass comparisons of species and aerosol components
M. O. Andreae