Evaluation of Methods for Measuring Carbonaceous Aerosol in Rainwater

1. Alexander Torres Tami Bond, Advisor Christopher Lehmann, Co-advisor October 26, 2011 University of Illinois at Urbana-Champaign Civil and Environmental Engineering NADP Annual Meeting and Scientific Symposium Evaluation of Methods for Measuring Carbonaceous Aerosol in Rainwater

2. Carbonaceous Aerosol • Black Carbon (BC) • Byproduct of the incomplete combustion of fossil fuels and biomass • Absorbs visible light and warms the atmosphere • 85% of the emitted mass is in particles < 0.2 µm diameter • Atmospheric concentrations range: • 0.2 to 2.0 µg/m3(rural) • 1.5 to 10 µg/m3 (urban) BC particles collected on a Millipore filter Diesel engines: high emitter

3. Carbonaceous Aerosol • Organic Carbon (OC) • Primary sources: • Combustion of fuels and biomass • Commercial products • Biogenic material • Secondary Source: • Oxidation of VOCs • Atmospheric concentrations range: • ~3.5 µg/m3 (rural) • 5 to 20 µg/m3 (urban) • Reflect light and coolthe atmosphere OC particles collected on a Millipore filter Fireplace: high emitter

4. Wet Deposition (WD) of Carbon Aerosols • Importance of the study: • WD is the most uncertain parameters in global circulation modeling of carbonaceous aerosols • Carbon particles comprises 25-70% of PM2.5 in USA • Measurements of OC and BC together are limited • Removal rates of OC and BC are different (70% of OC and 10% of BC is water soluble) • High variability in the reported BC lifetime: 40 hours to 1 month

5. Objectives of the study • Evaluate different analytical techniques to measure particulate and dissolved carbon in rain • Measure concentration of BC and OC in rain • Match precipitation data with atmospheric concentration which yields insights into BC and OC removal Bondville Environmental and Atmospheric Research Station, IL

6. Analytical Approach Rain Sample Rain Sample Pre-filtration Dissolved Carbon Particulate Carbon Quartz Fiber Filters Particulate Organic Carbon Black Carbon Dissolved Organic Carbon Dissolved Organic Carbon

7. Black Carbon: Analytical Method • Thermal-Optical Method (OC-EC Analyzer) • Measures particulate OC and BC • Samples are collected on a quartz fiber filter • Temperature ramps are used to desorb OC (O2-free environment) and BC (O2/He environment) and converted to CO2 • Light absorbance is used to separate OC and BC Quartz fiber membrane OC-EC Aerosol Analyzer, Sunset Laboratory

8. Black Carbon: Method Limitations • Experimental limitations • BC particles (in water) are too small to be collected on quartz fiber filters • Large biogenic material interferes with the analysis • BC concentration in rain is too low to be detected using 45 mm filters. Nuclepore filter (8 µm pore size)

9. Black Carbon: Method Improvement • Work-around • Pre filtration of the sample is necessary to remove biogenic material • Filtration area has to be reduced to get a low detection limit (140 ng/L) • Addition of a ionic compound is necessary to induce the BC particles agglomeration Funnel with fritted glass disk (~ 50 µm pore size) Small filtration device (filtration area= 0.7 cm2) Adding 3 drops of H3PO4 (25% v/v) Adding 1 g of (NH4)2SO4 / 100 mL Filtration Setup

10. Black Carbon: Method Improvement • Collection efficiency of the quartz fiber filter after adding a ionic compound No addition

11. Black Carbon: Method Improvement • Determination of the optimum amount of (NH4)2SO4 to be added to the rain sample 0.5 g

12. Dissolved Organic Carbon (DOC): Analytical Method • Total Organic Carbon (“TOC”) Analyzer • Combustion catalytic oxidation method • Low detection limit (4 µg/L) • Limitations • Requires 30 mL of sample • Susceptibility of the analysis to contamination • Work-around • Use rain samples with large volume • Use nitric acid bath for 24 hours and/or muffling at 450°C for 5 hours Shimadzu TOC 5000 Carbon Analyzer

13. Dissolved Organic Carbon:Preliminary Results • Comparison of the monthly mean concentration of DOC in rain vs. historical record of OC in air measured at Bondville, IL.

14. Dissolved Organic Carbon:Preliminary Results • Comparison of the measured DOC vs. concentration of ions in precipitation

15. Dissolved Organic Carbon:Preliminary Results • Mean mass fraction of DOC in precipitation measured at Bondville, IL

16. Dissolved Organic Carbon:Preliminary Results • Comparison of the DOC measurements vs. Ion Percent Difference (IPD) … an Indicator of the “missing” anions in the CAL’s measurements

17. Conclusions • Sampling of particulate BC and OC in rain employing quartz fiber membranes requires the reduction of the filtration area and the addition of a “salt” • Adding ionic compounds stimulates the BC particles interaction and agglomeration • Pre filtration, decontamination, and proper handling and conservation of rain samples is required to avoid contamination with OC • DOC in rain correlates with SO42-, NO3-, and Total Ions. • Organic compounds contributes to the ion balance of rain samples.

18. Acknowledgments • Illinois State Water Survey (National Atmospheric Deposition Program) • EPA STAR Fellowship Program • University of Puerto Rico at Mayaguez (UPRM) • Tami Bond research group at UIUC (http://hiwater.org/)