MEASUREMENT AND MODELING ANALYSIS OF ORGANIC AEROSOL AND THEIR CLOUD INTERACTIONS

Lynn M. Russell (SIO)

Link to NOAA Strategic Plan: NOAA's Mission Goal 2: Understand Climate Variability and Change to Enhance Society’s Ability to Plan and Respond

RESEARCH OBJECTIVES AND SPECIFIC PLANS TO ACHIEVE THEM

This proposal supports (1) continued and enhanced measurements of submicron particle composition using FTIR spectroscopy, XRF spectroscopy, and AMS measurements to obtain elements, functional groups, and quantitative organic mass as part of NOAA field studies, (2) extended NEXAFS/STXM of organic functional groups and their distribution in single particles as part of NOAA field studies, and (3) development and implementation of process modeling and laboratory measurements incorporating the phase, mixing state, and optical properties of the measured organic bonds, using model compounds and their measured properties.

RESEARCH ACCOMPLISHMENTS

During the second year of the project the organic functional group concentrations and the organic mass concentrations were calculated from calibration and measurements of ICARTT 2004 samples. The data analysis of chemical composition of organic aerosol was carried out, with particular attention to:

•            Average functional group composition of organic mass,
•            Temporal variation of functional group composition, and
•            Correlation between saturated and unsaturated aliphatic groups and oxidized functional groups.

During ICARTT 2004 the organic mass was dominated by the contribution of aliphatic saturated C-C-H and carbonyl C=O groups. Oxygenated functional groups (carbonyl C=O and organic hydroxyl C-OH) were observed on all platforms with concentrations that were often comparable to the saturated aliphatic C-C-H group concentration. The carbonyl C=O to saturated aliphatic C-C-H group molar ratios recorded on the R/V Ronald Brown and at Chebogue Point was 0.5. Some of the variability within the samples at each platform can be attributed to changes in air masses, with those air masses associated with similar regional sources also having comparable functional group composition. Retroplume analysis for Chebogue Point samples suggested that air masses that reached these locations from Canada, which showed TAG factors that were indicative of biogenic emissions, were characterized by higher carbonyl C=O group concentration relative to saturated aliphatic C-C-H groups, compared to those air masses dominated by U.S. sources. Intercomparison of independent techniques for measuring the total OM and OC at the two sampling locations showed general agreement. Measurements from the two techniques generally track each other with time but the linear correlations show high variability in the data. The analysis of organic sulfur compounds was made possible by optimizing a rinsing procedure to remove bisulfate and carbonate interference.

During the summer 2006, submicron aerosol samples were collected on the R/V Ron Brown, as part of the Texas 2006 campaign. Samples and field blanks were analyzed by FTIR for organic functional groups composition, and by XRF for elemental composition. FITR organic mass concentration was compared to AMS organic mass. Better agreement between FTIR and AMS was observed for OM concentrations lower than 10 µg m-3.

 

Fig.1 Temporal trends of the measured functional group composition: (a and b) Chebogue Point and (c and d) R/V Ron Brown. For each platform, the lower plot (Figures 1b and 1d) corresponds to functional group composition of cumulative samples (12 or 24 hour collection time), and the upper plot (Figures 1a and 1c) reports simultaneous shorter time samples (3, 4, 6 or 8 hour collection time). All panels show saturated aliphatic C-C-H groups (blue), organic hydroxyl C-OH groups from alcohol and carboxylic acids (pink), aromatic C=C-H groups (light blue), unsaturated aliphatic C=C-H groups (red), carbonyl C=O groups (green), and organic sulfur C-O-S groups (yellow) mass concentration.

 

Fig. 2 Temporal trend for organic mass as measured by FTIR (red) and AMS (grey). Black markers and lines show the average AMS organic mass for each FTIR collection period. Vertical error bars on FTIR points are one standard deviation. Horizontal error bars indicate the time period over which each filter was sampling. Inset: Correlation between FTIR and AMS organic mass (black open squares, black line). The best-fit line has a slope of 0.47 and an R2 value equal to 0.56. Those points corresponding to AMS average concentrations of less than 10 µg m-3 are filled in red (slope is 0.65, R2 is 0.53).