Sources of Organic Aerosols Soluble in Water in the Southeastern U.S.

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1 Sources of Organic Aerosols Soluble in Water in the Southeastern U.S. Amy P. Sullivan and R.J. Weber Georgia Institute of Technology Funding: NSF and NOAA

2 Motivation Outline Brief overview of methods for water-soluble organic carbon (WSOC) Components of PILS-TOC (On-line) Group speciation of WSOC involving XAD-8 resin and Size-Exclusion Chromatography (SEC) (Off-line) Ambient results from urban Atlanta and its surrounding regions during summer Airborne on-line WSOC measurements Off-line WSOC group speciation at various locations Summary

3 Motivation Sources of organic carbon (OC) not fully known Using EC (elemental carbon) tracer method, suggested in Atlanta 50% of OC secondary, but can be near 90% on short time scales [Lim and Turpin, ES&T, 2002] Chamber studies show biogenic emissions are readily oxidized to form Secondary Organic Aerosol (SOA) Southeastern urban centers densely forested with coniferous trees leading to speculation that biogenic precursors major contributor to SOA

4 How can WSOC measurements help? SOA formation is thought to be one of the major sources of WSOC Implies that methods developed for separation and analysis of WSOC could be used to investigate SOA products

5 Method 1: On-line Measurement of WSOC Particle Size Selector (PM 1 ) Schematic of PILS-TOC Teflon Filter (Background) Vacuum Pump Transport Liquid Flow via syringe pumps Valve Drain Activated Carbon Denuder steam Drains Debubbler Liquid Sample via syringe pumps Liquid Filter -Limit of Detection = 0.1 µg C/m 3 -Sampling rate = 3 s Sievers TOC tee Drain

6 Method 2: Off-line Group Speciation of WSOC Aerosol Organic Carbon Water- Insoluble OC Step 1 XAD-8 Hydrophilic Step 2 SEC Aliphatic Acids Neutrals Bases Water- Soluble OC Hydrophobic Unrecovered Hydrophobic Recovered Acids Neutrals -Analysis performed on Hi-Volume integrated filters

7 XAD-8 Calibration (based on 36 standards) Mono-, Di-, Oxocarboxylic Aliphatic Acids Carbonyls Saccharides Amines Aromatics Cyclic Acids Organic Nitrates 100% Penetration 0% Penetration Hydrophilic Recovered Unrecovered Hydrophobic Hydrophobic Carbons < 4 Carbons > 4 Carbons < 4 Carbons > 4 X X X X X

8 Modified SEC Method WSOC, Hydrophilic, or Recovered Hydrophobic Sample -By not adjusting ionic strength and buffering sample (ph 6.8) obtain separation by functional groups S E C Total Organic Carbon Analyzer Concentration (ppb C) 20x Hydrophilic Calibration C2 - diacid C3 - diacid HYDROPHILIC ALIPHATIC ACIDS HYDROPHILIC NEUTRALS levoglucosan HYDROPHILIC BASES ethanolamine 0 00:20 00:25 00:30 00:35 00:40 00:45 00:50 00:55 Tr (min)

ICARTT: ITCT 2004 Latitude (degrees) 55 50 45

9 ICARTT: ITCT 2004 Latitude (degrees) Longitude (degrees)

10 WSOC ( µg C/m 3 ) Non-Biomass Surface Source WSOC versus CO y = -2.2± x±0.01 R 2 = (acetonitrile < 200 pptv and altitude < 2 km) New York City Plume All Data CO (ppbv) 250 -WSOC-CO R 2 = 0.53, fairly well correlated CO: J.S. Holloway, NOAA-ESRL/CIRES Acetonitrile: J.A. de Gouw and C. Warneke, NOAA-ESRL/CIRES 300 Altitude (m) WSOC CO WSOC 16:25 16:30 16:35 16:40 16:45 Time (UTC) CO (ppbv) -WSOC-CO R 2 = 0.82, highly correlated in specific urban plumes

11 WSOC Evolution in Urban Plumes Latitude (degrees) A 0721B 0814B 0814B' 0720B 0720A 0814A 0814A' -Back trajectories of WSOC plumes that intercepted NYC WSOC/ CO (/ppmv) Longitude (degrees) 0720A B A' 0814A B 0814B' A Advection Time from Urban Center (hours) 0721B 35 WSOC/ CO Lowest near city Begins to level off after ~ 1 day to 32 ± 4 /ppmv WSOC produced from compounds co-emitted with CO Urban emissions rapidly converted to secondary products?

-Wide spread elevated CO and WSOC in boundary layer Atlanta Flyby 5000 4000 3000 2000 1000 0 6 -WSOC-CO R 2 = 0.

12 -Wide spread elevated CO and WSOC in boundary layer Atlanta Flyby WSOC-CO R 2 = 0.83 (excluding in-cloud) -WSOC doesn t track in fresher CO plumes - WSOC/ CO ~33 ± 5 /ppmv, similar to NYC (32 ± 4) Altitude (m) WSOC Cloud Penetration A Aircraft directly over Atlanta B CO 18:00 18:30 19:00 19:30 20:00 Time (UTC) C WSOC D E CO (ppbv)

Sampling Sites for WSOC Group Speciation Next to

(during period of poor air quality) Hi-Volume

13 Sampling Sites for WSOC Group Speciation Next to I-75/85 ~400 m from GIT and ~1 m from highway Georgia Institute of Technology (GIT) Roof top of ES&T Building Yorkville, GA ~80 km west of GIT (during period of poor air quality) Hi-Volume Samplers: B. Yan and M. Zheng, Georgia Institute of Technology

14 GIT vs. Highway GIT vs. Yorkville From: m 400 m 80 km

15 Carbonaceous Aerosol Comparison Site EC OC WSOC WSOC OC Highway GIT Yorkville GIT Results from 2 separate paired experiments

16 Carbonaceous Aerosol Comparison Site EC OC WSOC WSOC OC Highway GIT Yorkville GIT EC = primary Highest by highway (GIT vs. Highway) Highest in urban center (GIT vs. Yorkville)

17 Carbonaceous Aerosol Comparison Site EC OC WSOC WSOC OC Highway GIT Yorkville GIT OC = primary and secondary, less difference

18 Carbonaceous Aerosol Comparison Site EC OC WSOC WSOC OC Highway GIT Yorkville GIT WSOC little variability -Most compounds comprising WSOC not directly from mobile sources (NOT PRIMARY)

19 Carbonaceous Aerosol Comparison Site EC OC WSOC WSOC OC Highway GIT Yorkville GIT Higher ratio further from mobile sources due to smaller influence from primary emissions and driven more by spatial variability of primary OC

20 Three Main Chemical Components of WSOC Includes expected biogenic SOA products 1% 6% 9% 11% 1 36% GIT 2005 during PM Event WSOC/OC = % 3 2 1% 21% 1.Hydrophilic aliphatic acids, e.g., C < 4 acids 2.Hydrophilic neutrals, e.g. saccharides and C< 4 carbonyls 3.Recovered hydrophobic acids, e.g. aromatic acids or compounds with similar properties

21 Correlations of Three Main WSOC fractions (all data) GIT 2004 R 2 = 0.87 GIT 2005 Yorkville R 2 = 0.81 Highway 1 vs. 2 1 vs. 3 2 vs R 2 = Hydrophilic aliphatic acids and neutrals and recovered hydrophobic acids all correlated, near-zero intercepts -Suggests their sources are all linked

22 Mass Balance on Measured VOCs and OC (POM) from NEAQS 2002 From: J.A. de Gouw et al., JGR, 2005 Secondary Primary VOCs Alkanes largest - mass -SOA: little evidence for biogenic, not explained by aromatic VOCs

23 Summary In summer urban Atlanta and its surrounding areas WSOC has a regional characteristic and its source appears to be largely SOA Spatially uniform compared to primary particles (e.g., EC), thus likely not primary No clear evidence for strong biogenic SOA signal, instead points to precursors from mobile sources Supported by: High WSOC-CO correlations on large spatial scale Similar WSOC/ CO in Atlanta and NYC Known biogenic products small fraction of WSOC

24 Summer WSOC composition: 1. Hydrophilic aliphatic acids 2. Hydrophilic neutrals 3. Recovered hydrophobic acids -All correlated suggesting linked sources Implication that mobile source emissions may play a large role in the formation of WSOC in urban regions in the southeastern U.S. For more details on WSOC group speciation methods see poster A33B-0876 on Wed. afternoon

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