I would like to thank Tracey and Tomtor, who took me under their wings in the field. I was very pleased to have been able to work closely with Scott over the past year and a half.
List of Tables
Summary of measurements in and outside smoke of composition and particle number and mass concentration Table 7.2.
Specified size distributions as determined by cToF-AMS for flights A (panel A) and B (panel B)………303 Figure 7.13. Time series of activated aerosol fraction (CCN/CN) and total CCN concentration during flights A (upper panel) and B (lower panel)……….307 Figure 7.17.
Introduction
Background and Motivation
To understand the relationship between aerosols and climate, measurements of key aerosol properties must be made, including the following: size distribution, number concentration, composition, hygroscopicity, and refractive index. One way to reduce the uncertainty in the radiative forcing associated with aerosol effects is to perform in situ measurements of atmospheric aerosols in the environment.
Organization of Thesis
Furthermore, the addition of free tropospheric aerosol is also argued to lead to increased organic acid levels above clouds. Organic acid bulk composition in the Houston Ship Channel, an area emitting large amounts of aromatic hydrocarbons, is compared with measurements from laboratory studies of m-xylene photooxidation.
Modeling and Characterization of a Particle-Into- Liquid Sampler (PILS) ∗
Abstract
A model is developed to predict aerosol mass concentrations measured by a PILS based on operating parameters and characteristics of the sampled aerosol. A backward model predicts the concentrations of the sampled aerosol based on operating parameters and concentrations measured by the PILS.
Introduction
A model is needed to predict sample behavior in both the original and modified PILS to quantify effects such as evaporation loss and mixing. The two models are used to simulate the operation of both the modified and the original PILS, where the step involving the syringes is eliminated when considering the original PILS.
Modified PILS
The condensation chamber is held at a slight angle (15°) to allow wall condensate to be removed by a drain line at the end. The time lag can be reduced by lowering the dwell time of the debobbler; this involves optimizing the relationship between the flow rate of the wash stream at the top of the drop impact body and the speed of the sprayers that suck liquid from the debubbler.
PILS Model
- Model Equations
- Model Predictions
It is assumed that before the sampled aerosol reaches the condensation chamber, the denudes remove all the gas phase species (NH3, HCl, HNO3). Losses during the droplet growth stage are dominated by gravitational settling and inertial deposition in the main body of the condensation chamber and in the conical section at the end of the chamber (these areas are defined in Figure 2.2).
PILS-IC Detection Levels
- Ion Chromatography (IC) System
- PILS-IC Technique Background Levels
Tests were performed to check if there are any sinks or sources for the different species (NH4+, SO42- or NO3-) in the fixtures between the impact plate and the tap needle. This test would also show whether the heating of the impinger plate due to warm droplet deposition and convective heating leads to a loss of volatility for either species in the wash stream solutions.
Evaluation of Model With Laboratory Data
- PILS Collection Efficiency for Different Aerosol Seeds
- Tip Temperature Sensitivity Tests
The collection efficiency of the PILS compared to the DMA and the molar ratios measured in the PILS vials, as total averages, are shown in Tables 2.5 and 2.6, respectively. Theoretical calculations for NH4+ losses in the PILS in Figure 2.6 show consistency with the experimental observations.
Field Data
Future Work
The PILS can also be connected to other analytical detectors to quantify organic substances other than the organic acids that the IC can detect. Techniques such as these increase the fraction of total particulate organic mass that the PILS can specify and quantify.
Conclusions
The predictions show intermediate agreement with experimental data from the modified PILS, with the main problem being that the model cannot fully unfold the mixing effects within the PILS during the transition between step changes. Results of laboratory characterization tests of the sampling efficiency and volatilization losses within the PILS were compared with model predictions and good agreement was found.
Acknowledgements
The "P" and "D" markers indicate which equations from Table 2.1 are applied in the designated stages of the PILS. The (a) total transmission efficiency in the room is shown in addition to the (b) relative contribution of different parts of the room to the total losses.
Rapid Size-Resolved Aerosol Hygroscopic Growth Measurements: Differential Aerosol Sizing and
Abstract
Excellent agreement is obtained between DASH-SP laboratory data and thermodynamic model predictions for the dependence of growth factors on relative humidity for various inorganic salts. Airborne measurements of hygroscopic growth factors from ship exhaust aerosol during the 2007 Marine Stratus/Stratocumulus Experiment (MASE II) field campaign off the central coast of California are presented as the first report of the aircraft integration of the DASH-SP.
Introduction
RH-DMOPSS, which is an extension of the DMOPSS design of Stolzenburg et al. 1998), measures drying shrinkage rather than wetting growth like most other hygroscopic growth instruments. Depending on the concentration and size distribution of the sampled aerosol, particle growth factors at any selected size within the instrument's size resolution can be determined in seconds.
DASH-SP Description
The design of the laser light sheet is such that all particles entering the OPC optical cavity pass through the light. By multiplying the speed by the transit time, the thickness of the laser light sheet is determined.
Experimental Methods
Instrument Characterization .1 Size Limits of OPC Detection .1 Size Limits of OPC Detection
- Time Resolution
- DASH-SP Accuracy, Precision, and Uncertainties
- Stability
The uncertainty of the DASH-SP measurement of the growth factor depends on the uncertainties in the RV and sizing measurements (DMA and OPC). Particles detected by the OPC corresponded to sizes below the 50% detection limit of the OPC (Dp < 135 nm).
Data Analysis
Before pulse height distribution modes can be used to determine particle size and refractive index, dry particle calibrations must be performed to gather sufficient data on pulse height, particle size, and refractive index. Using the wet particle pulse height data, iterations are performed on the three-dimensional surface to converge to a value for the "effective" wet particle refractive index, which is then used to determine the wet particle diameter and growth factor.
Growth Factor Measurements .1 Inorganic Salts .1 Inorganic Salts
- Organic Acids
This result is consistent with previous studies which showed that organic acids absorb water at all RHs (Saxena and Hildemann, 1997; Dougle et al., 1998). Growth factors for malonic acid showed the best agreement with predictions compared to other organic acids, with a growth factor that is at most 6% below that predicted.
Validation of Iterative Data Processing Code
We would expect narrower size distributions for the dry ammonium sulfate results in Figure 3.8 since DMA selects one size. To determine whether the width of the size distribution of dry ammonium sulfate is due to an instrument problem or impurities and morphological problems associated with ammonium sulfate particles, the size distributions of dry PSL were also calculated, since PSL particles are spherical (Figure 3.8D).
Field Implementation of DASH-SP
However, it is possible that some of the broadening is also due to particles experiencing the RH type. The average dry "effective" refractive index of the aerosol in the ship cloud was found to be the same, while the "effective" refractive index of the background aerosol was outside the cloud.
Conclusions
The temporal resolution of DASH-SP can be seen in Figure 3.9C, which shows the spatial distribution of growth factors at RH 92%. A high degree of stability exists in dry salt calibrations and growth factors for various salts at RH up to 92%, especially for particle diameters greater than 50% of the OPC detection limit.
Acknowledgements
Growth factor data for organic acids show that, with the exception of oxalic and glyoxylic acids (both C2 acids), the organic acids with odd numbers of carbon atoms (malonic and glutaric acids) exhibit greater hygroscopic growth than those with even numbers (succinic acid). and adipic acids). Succinic and adipic acids show no hygroscopic growth up to a RH of 94%, while the other organic acids show gradual growth starting at low RH (< 65%).
Water-Soluble Organics in Atmospheric Particles: A Critical Review of the Literature and the Application of Thermodynamics to Identify Candidate Compounds, J. Estimating the Volume Fraction of Water-Soluble Material in Sub-Micron Aerosols in the Atmosphere, J.
Oxalic Acid in Clear and Cloudy Atmospheres
Analysis of Data from International Consortium for Atmospheric Research on Transport and
Abstract
The relative contributions of the two aqueous phase routes responsible for oxalic acid formation were investigated; the oxidation of glyoxylic acid was predicted to dominate over the decay of longer chain dicarboxylic acids. Clear evidence is presented for aqueous-phase oxalic acid production as the primary mechanism for oxalic acid formation in ambient aerosols.
Introduction
During ICARTT we analyze airborne measurements of SO42 and oxalate under various conditions in the atmosphere around Ohio. We investigate the correlation between SO42 and oxalate, and the role of other organic acids in the aqueous phase production of oxalate.
Twin Otter (TO) Research Aircraft
The aim of the present work is to explain oxalic acid formation in the atmosphere. This transfer efficiency persists for particle diameters up to 9 μm, the upper limit of the characterization tests.
PILS-IC Measurements
- Case Study: Power Plant Plume in Cloud (Flight 5 on 9 August 2004)
Flight 5, the flight with most data points representing the cloud power plant plume, will be discussed in the next section. There is a significant increase in SO42-, oxalate, and volume concentration of aerosols in the cloud that continues upwind of the plant.
Cloud Parcel Model
- Description and Modifications
- Sensitivity Analysis
In addition, some volatile organic species, including HCHO and CO2, are produced as byproducts in the aqueous phase mechanism and do not contribute to oxalic acid production. The baseline value of 500 m used for b in the accretion rate was doubled and halved to explore the sensitivity of SO42- and oxalic acid production rates to this parameterized factor.
Comparison of Model Predictions to Field Measurements
- Case Study: Power Plant Plume in Cloud
- Case Study: Clouds Uninfluenced by Local Pollution Sources
- Comparison of Predictions From Both Cases to all In-Cloud Field Measurements
- Contribution of Different Aqueous-Phase Pathways to Production of Oxalic Acid
Oxalic acid reaches a peak mass of 0.38 μg/m3 after the sixth cloud cycle before gradually decreasing to 0.17 μg/m3 by the end of the simulation. The concentrations of glyoxylic acid precursors (including acetic, pyruvic and glycolic acids) are also said to be higher in this case, indicating that mechanisms related to toluene, ethene and isoprene (only these three parent organic species produce glyoxylic acid) are more efficient in the production oxalic acid.
Conclusions
Oxalic acid production has been shown to increase with increasing amounts of both LWC and pH in droplets. Based on a state-of-the-art chemical mechanism in the aqueous phase, the oxidation of glyoxylic acid dominates over that of longer chain dicarboxylic acids in the production of oxalic acid.
Acknowledgments
Sakaguchi (1999), Molecular distributions of water-soluble dicarboxylic acids in marine aerosols over the Pacific including tropics, J. Huebert (2003), Water-soluble dicarboxylic acids in the tropospheric aerosols collected over East Asia and western North Pacific by ACE-Asia is C-130 aircraft, J.
On the Source of Organic Acid Aerosol Layers Above Clouds ∗
- Abstract
- Introduction
- Aircraft Measurements
- Sources of Oxalate above Cloud
- Physical Processes at the Cloudtop Interface (Large Eddy Simulations)
- Oxalic Acid Chemistry
- Methanesulfonate
- Acknowledgements
- References
Organic aerosol layers present above clouds with increased organic acid levels were observed at both sites. Three of these events exhibited lower particulate oxalate and organic acid concentrations above the cloud compared to below.
