Aerosol Life Cycle IOP
The primary objectives that make up the Aerosol Life Cycle IOP can be
broken down into three categories: Scientific; Logistical; and GVAX
preparation.
Scientific Objectives
The science goals are to conduct intensive aerosol observations in a
region exposed to anthropogenic, biogenic, and marine emissions with
atmospheric processing times depending on air mass trajectories and time
of day. Take advantage of new instruments in the MAOS (e.g., SP2,
HR-PTRMS, ACSM, Trace Gas Suite, PASS-3, Aethelometer, UHSAS). Within
this broad umbrella are embedded three main foci:
- Aerosol light absorption: How does
the aerosol mass absorption coefficient (absorption per
unit mass of BC) vary with atmospheric processing? Do
observations agree with a shell-core model?
- Secondary organic aerosol (SOA): How does the amount and formation rate of SOA vary with
atmospheric processing and sources? Can heretofore
unavailable measurements of oxygenated VOCs (from high
resolution PTR-MS) explain the excess SOA observed in
other locations?
- Aerosol as CCN: What is the effect
of different organic components on CCN formation?
Studies of BC, SOA, and CCN are briefly described below. A key
component of these three focus areas is that aerosol properties will be
determined as function of atmospheric processing and chemical conditions
or source type. Sources of aerosols and their precursors will be
determined from chemical tracers (e.g., CO, CH3CN, other VOCs, and SO2).
Atmospheric processing will be determined from back trajectories and
photochemical age.
- Optical effects of BC. BC mass concentration from the SP2 will be
combined with light absorption measurements (PSAP, PASS, and PTI) to
determine a mass absorption coefficient. Coating thickness will be
determined from the SP2 using its luminescence and scattering channels
(thin/thick coating) and by comparing aerosol size distributions with
and without a thermal denuder. Aerosol composition from the thermal
denuder and from the AMS and PILS will provide information on the
coating material. Theory and observations will be compared.
- SOA Formation. Total OA concentration, along with that of NH4, SO4
and NO3, will be determined using an Aerodyne Aerosol Mass Spectrometer
(AMS). Concentrations of SOA will be approximated by oxygenated-OA (OOA)
evaluated from factor analysis of the AMS data (such as the PMF). CO is
a good tracer for urban emissions and will be used to assess extent of
dilution during transport. Black carbon (by SP2) will be used to
estimate primary organic aerosol (POA) using a known emission ratio at
the source, which can be checked against the POA taken as the
hydrocarbon-like OA (HOA) estimated also from factor analysis. Volatile
and oxygenated organic compounds will be quantified using a high
resolution Proton Transfer Reaction Mass Spectrometer (HR-PTRMS),
which provides source information based on relative abundance of
anthropogenic and biogenic compounds (e.g., benzene vs. isoprene/methyl
vinyl ketone) as well as photochemical age (e.g. benzene/toluene
ratio).The distinguishing feature of this study is high mass resolution
so that oxygenated VOCs can be differentiated from hydrocarbons of
nearly the same mass. By following the oxygen content, the HR-PTRMS
offers a measure of the extent of VOC oxidation in an air mass. We will
investigate the dependence of the extent and rate of SOA formation upon
VOC oxidation. Theories that predict that excess SOA is due to the
condensation of oxygenated VOCs will be tested and perhaps key
oxygenated species involved in SOA formation will be revealed.
- Cloud Condensation Nuclei (CCN). The cloud activation properties
of major aerosol organic classes will be determined from simultaneous
size-resolved measurements of CCN spectra, mixing state (HTDMA in
MAOS-A), and particle composition. These measured CCN properties of
organic classes can be conveniently incorporated into parameterizations
for improved representation of aerosol-cloud interaction in global
climate models. Based on measured aerosol size distribution and
composition, CCN spectra will be calculated using various simplified
representations of aerosol composition, and compared to direct
measurements.
- Model-Observation Intercomparison. Tying the measurement efforts
described above will be a parallel effort to examine how well models can
reproduce the observed optical properties (including RH dependence) and
CCN properties (number vs supersaturation) when using the measured size
dependent chemical composition as input. This will involve developing a
modeled representation of the observed chemical and microphysical
properties that can be used as input to the various models that will
evaluated. Potential candidate models that will be examined include WRF-Chem,
box model for MOSAIC and CAM5.
Kleinman, L. I., Daum, P. H., Imre, D. G., Lee, J. H., Lee, Y.-N.,
Nunnermacker, L. J., Springston, S. R., Weinstein-Lloyd, J., and Newman,
L., 2000, Ozone production in the New York City Urban Plume. J. Geophys.
Res. 105, 14,495-14,511.
Logistical Objectives
The ARM Climate Research Facility Mobile Aerosol Observing
System (MAOS) is a state-of-the-art mobile laboratory for measurement of
aerosol optical and microphysical properties. More specifically, MAOS is
a platform and instrument package for deployment in the field during
Intensive Operation Periods (IOP) to make in-situ measurements of
aerosols and their precursors. Physically MAOS is contained in two SeaTainers custom adapted to provide a sheltered laboratory environment
for operators and instruments even under harsh conditions. The two
structures are designate d MAOS-A and MAOS-C for Aerosol and Chemistry
respectively. Although independent, with separate data systems, inlets
and power distribution, the two structures should be considered as a
single operating unit. MAOS represents an entirely new ACRF platform and
thus must have a new operational strategy developed and tested to
maximize the very rich data set that this platform will provide to the
ARM community. Deployment at the Aerosol Lifecycle IOP will help
facilitate this development and testing. This activity must be
undertaken because this platform contains several state-of-the-art
instruments that require either highly skilled operators or require 1-2
hours of instrument-specific servicing daily. Chief among these operator
intensive instruments are the PTRMS (proton transfer reaction mass spec)
and PILS (particle in liquid sampler). It is because of these
instruments and others (e.g., SP2 with voluminous data output) that an
operational strategy analogous to that utilized for aircraft operations
(IOP-type strategy) must be developed and tested. However, the
aircraft-based strategy can only serve as a starting point because
unlike aircraft operations, where intensive data acquisition occurs
during a finite period of time (e.g., 4 hr flight of the G1) the MAOS
will run 24/7 for the duration of an IOP (4-8 wks). During the proposed
BNL IOP, various operational strategies will be tested and evaluated in
preparation for this platform's maiden international deployment in India
as part of the
2012
GVAX. Additionally, this work will provide invaluable guidance as to
the level of technician support that will be needed to operate MAOS-C
during an IOP and how much training of the technicians will be required
(see below).
Ganges Valley Aerosol Experiment (GVAX)
In preparation for the
GVAX
field campaign, this Aerosol Life Cycle IOP will provide the
opportunity to train colleagues from the Indian Institute of Science (IIoS)
who will be providing day-to-day operational support to the MAOS
platform during its 2-month deployment in the Ganges Valley. As
currently envisioned, 5 scientists/engineers will arrive at BNL for a
4-week intensive training period that will cover all aspects of the MAOS
instrument suite operation, maintenance and first-order trouble shooting
as well as nominal platform infrastructure operations and overall MAOS
operational strategies deployed under the Logistical objective.