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Aerosol Chemistry & Microphysics

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: 

  1. 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? 
  2. 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? 
  3. 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. 

  1. 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. 
  2. 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. 
  3. 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. 
  4. 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.