SEASONAL VARIABILITY OF ORGANIC MASS CONTRIBUTION TO PM2.5 WITHIN METRO ATLANTA AND FURTHER DOWNWIND K. Baumann 1, M.E. Chang 1, A.G. Russell 2, E.S. Edgerton 3 1 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta 2 School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta 3 Aerosol Research and Analysis Inc., Cary, NC  Long-Term Observations in South-Central GA  Aerosol Characterization in July 01 and January 02  Estimate Photochemical Activity and OCs  Identify Enrichment of Individual Species During Transport Acknowledgement: S. Lee, H. Park, M. Bergin, R. Weber, all GA Tech Funding provided by US-EPA and GA-EPD (FAQS)

2 Network Measurement Sites, SO 2 GRF FAQS Period Jul’00 - Sep’03 MAY - OCT NOV – APR JST Period AUG’99

3 GRF FAQS Period Jul’00 - Sep’03 MAY - OCT NOV – APR JST Period AUG’99 GRF CO

4 NOy GRF FAQS Period Jul’00 - Sep’03 MAY - OCT NOV – APR JST Period AUG’99 GRF

5 O3O3 FAQS Period Jul’00 - Sep’03 MAY - OCT NOV – APR JST Period AUG’99 GRF

6 PM 2.5 GRF FAQS Period Jul’00 - Sep’03 MAY - OCT NOV – APR JST Period AUG’99 GRF

7 Summertime PM 2.5 – Max(O 3 ) Relationship Tighter correlation in July “Downwind” Griffin site offset to higher PM 2.5 mass. What was different in August 1999?

8 Prescribed Burns in Georgia 37,320 16,250 > 117, = OC/EC ratio EF(OC) ~ 10 g/kg EC/CO ~ 0.4 ±0.2 flaming ~ 3.3 ±0.7 smolder OM/OC ~ 1.5 ±0.7. OC/EC ~ 16 ±18 See Lee et al., 13A3 on Wednesday !!

9 Urban / Rural Seasonal Trend in OC/EC and OM/OC Regional Difference: Higher OM/OC and OC/EC at more rural site. More OCs (SOA) in Aug-99 and more oxygenated POC away from Atlanta. Seasonal Difference: Lower OM/OC and higher (?) OC/EC in winter. August 1999 in Atlanta was hotter, dryer, more polluted (incl. NH3?).

10 Comparison of Average Diurnal Pollution Levels

11 July 2001 Source - Receptor Considerations: The Big Picture Atlanta Jeff. St. Griffin Bledsoe Farm 50 km N S

12 July 2001 Source – Receptor Considerations: CO/NOy Air mass arriving at Griffin has significantly higher CO/NOy ratio in summer than in winter: Loss of more abundant summertime HNO 3 due to surface deposition! downwind Higher intercept points to elevated regional background CO! Long-range transport of wild fire plumes from Canada (see SOS’95) or effect from more local PB within GA?

13 Elevated regional O 3 background reflected in regression’s intercept: higher in Aug 99! At JST higher intercept and slope during Aug ’99 (OPE= 4 vs 3): more efficient P(O 3 ). OPE in air mass arriving at Griffin is likely larger given by upper and lower limits. Lower limit assumes 1 st order loss of HNO 3 due to surface deposition at k ≈ 0.3 ±0.1 h -1, which is similar to recent study [Neuman et al., 2004] but signif. higher than prev. derived from v dep. July 2001 Source – Receptor Considerations: O 3 /NOz as “OPE” downwind

14 July 2001 Source – Receptor Considerations: Primary OC Using EC-Tracer approach [Gray 1986, Turpin et al. 1996, Cabada et al. 2002]: OCs = OC – OCp, with OCp = (OC/EC)p * EC + b Careful selection of days (samples) dominated by primary pollution using photochemical tracers incl. aerosol acidity yields:  Non-combustion (biogenic?) contribution b seems spatially and seasonally independent.  (OC/EC)p significantly higher at more rural GRF site at all times.

15 Seasonal Comparison of Estimated Secondary OC  Assuming (OC/EC)p and b constant for Atlanta JST site and applying derived values from Jul-01 data, OCs/OC varies between 64 and 70 % in Aug-99, depending on TOT or Relative Reference data.  OCs fraction was significantly less at JST in Jul-01 between 14 % for northerly flow, and 10 % for all other flow conditions.  The GRF site’s OCs/OC is significantly larger than JST’s but remains ~50 % whether downwind from JST or not.  The high OCs/OC at GRF in Jan-02 under non-NF is accompanied by large OC/EC (19 ±9) and small EC/CO (0.6 ±0.1  g/mg), indicating a possible influence from prescribed burning (days and locations not confirmed yet).

16 Seasonal Differences in Source – Receptor Relationships  High P(O3) and OPE leads to high OM/OC (>2) region wide, but >30 % more OCs/OC and higher aerosol acidity (ammonium, sulfate, nitrate system) at receptor.  EC/CO sensitive to TOR vs. TOT, but source receptor gradient and seasonal difference may be due to different fuel mix; e.g. residential wood & prescribed burning.  Slightly more NO 3 - formed than SO 4 = by time the air mass arrives at GRF in summer, and %- nitrate of N(V) reservoir increased also due to apparent HNO 3 deposition.  Strong change in acidic aerosol products from more nitrate in urban center to more sulfate in rural downwind site under simultaneous increase in %-ammonium of N(-III) reservoir. Comparing days when GRF was predominantly under N-ly flow, i.e. downwind from JST.

17 CO-referenced “Enrichment Factors”  Ammonium sources and sinks balance in summer, sinks dominate in winter.  Nitrate sources enhanced in winter due to reduced HNO 3 volatility (ambient RH at GRF reaches DRH and NH 3 *HNO 3 high enough to sustain solid NH 4 NO 3 most days.  N(V) reservoir almost balanced in summer but sinks dominate in winter.  S-compounds “enriched” due to coal PP emissions sources but highly variable due to limited data set; photochemical sulfate source ineffective in winter.  Biogenic (?) LOA sources enhanced by photochemical sources in summer; sources and sinks almost balanced in winter with slight enhancement from winter burns?  Different fuel mix in winter (increased wood burning with low EC/CO) may falsely enhance the deposition loss apparent in summer. CO was used due to lack of another more suitable tracer, e.g. Na +, or Al 2 O 3

18 Summary  Photochemical processes leading to high O 3 also lead to high PM 2.5 levels and increased aerosol acidity in air masses that are transported across Georgia.  Elevated levels of primary pollutants (CO, NOx, SO 2 and NH 3 ) and favorable met conditions responsible for high PM 2.5 mass concentrations during August  Possible regional impact from state wide prescribed burns of ~2 times the acreage in July 2001 causing high OC/EC and elevated background CO in August  First order NOy loss of observed ~70 % translates to k = 0.3 ±0.1 h -1, i.e. very rapid HNO 3 deposition enhancing the CO/NOy intercept (CO background).  OCs at JST in Aug-99 estimated at % depending on Rel. Ref. vs. TOT data.  As the Atlanta urban plume advects over BHC-rich terrain, it transitions to a more NOx-limited regime with greater RO 2 abundance, indicated by an increasing OPE.  This transition bears potential for formation of SOA, explaining OC/EC increase; high OM/OC levels indicative of more oxygenated POC appear more region wide.  The receptor’s OC is up to 50 % secondary in summer, which is ~30% more than observed at the urban air mass origin during the same time period.  The prescribed burn ban for Metro Atlanta may contribute to the observed higher (OC/EC)p especially in winter.

19 Supplementary Material

20 Seasonal and Regional Differences in OC/EC

21 PCM

22 Seasonal and Regional Differences in Composition

23 Seasonal/Regional Aerosol Acidity Based on [SO 4 = /NO 3 - /NH 4 + ] Aerosol is closely neutralized / slightly alkaline in winter but more acidic in summer Acidity caused by insufficient NH 3, or unaccounted for organic amines (with higher OM/OC)?

24 From CO/NOy regressions JST vs GRF: NOy init = 31/9 *NOy NOy lost = NOy init - NOy = NOy init *(1-9/31) = 0.71*NOy init Assume 1 st order loss: NOy init = NOy / exp(-kt) Assume 3.7 m/s N-ly flow throughout CBL: Then t = 4 h And k = 0.3 h -1