K. Baumann, F. Ift, J.Z. Zhao, M.H. Bergin, A.G. Russell, W.L. Chameides

1. Measurements of Trace Gases and PM2.5 Mass and Composition near the Ground and at 254 m agl During TexAQS 2000 and Comparison with Other Regions Acknowledgement: J. Lester, University of Houston, Clearlake R. Weber, D. Orsini, D. DiPasquale, W. Younger, all Georgia Tech Work sponsored by U.S. EPA through NCER Grant R826372 K. Baumann, F. Ift, J.Z. Zhao, M.H. Bergin, A.G. Russell, W.L. Chameides School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta • Tools and data quality • PM2.5 and O3 relationships • Episodes • Seasonal and regional trends in PM2.5 mass and composition

2. Particle Composition Monitor “PCM” More details described in paper accepted to JGR “Atlanta Supersite” special section, coming out soon…

3. Assessing Accuracy of PCM Measurements S-compounds and mass agree well, volatile species esp. NO3- more difficult to measure accurately

4. Direct emissions and/or secondary formation of fine PM aloft Motivation During SOS’99, 16 June - 22 July 1999, measurements near Nashville, TN, between 4 and 42 m agl showed positive vertical gradients for 60-70 % of all daytime, and 70-80 % of all nighttime samples of PM2.5 mass, SO4=, NO3-, and NH4+!!

5. WT-O3 levels are significantly higher early mornings and lower at midday Positive vertical [PM2.5] ‘gradients’ favored more often at night than at day, similar to Hendersonville Differences in [O3] and [PM2.5] Based on 30 min Averages

6. High Ozone and Biomass Burning Episodes LP max [O3] on 08/30 is more than twice WT-[O3], which more seems to follow a “rising tide”. In contrast: [PM2.5] only slightly different and in fact higher average on 08/29. BB plume on 9/5: max [NOy] and alkaline aerosol at LP only (!) but joint increase in mass.

7. High Ozone and Biomass Burning Episodes, continued Increases in SO4= mass fraction preceded by high [SO2] episodes, coinciding with max [O3]. Largest increase in TOC m.f. on day w/max [O3] & [SO2] and signature of traffic emissions. Maximum [CO] & [LOA]g associated with BB plume on 9/5 but [NH3] high at LP only!

8. 12.1+-2.8 22.2+-8.3 19.7+-4.6 Macon, GA Late June Augusta, GA Early July Columbus, GA Late July Sequential measurements at GA sites captured different episodes ! Regional Comparison of Average PM2.5 Composition in 2000 Williams Tower 16.4+-8.8 La Porte 16.0+-8.0 Entire period mid August to mid September

9. 15.2+-5.7 13.0+-4.7 19.0+-9.3 11.5+-4.0 Fall ‘99 Winter’99/’00 Seasonal Comparison of Average PM2.5 Composition 26.0+-11.7 Hendersonville 29.6+-12 Dixon Summer ‘99 • Differences in composition are insignificant regionally but not seasonally • Differences in mass related to different BL dynamics

10. Comparison of Seasonal and Regional Averages - incl. China • Significantly higher [PM2.5] at Yangtze sites in fall, even relative to U.S. summer • [O3] comparable in fall, but much higher in summer, esp. in U.S. metro areas • [O3] build-up observed in both summers and regions, TN&GA / GA&TX • [PM2.5] generally correlates with max [O3] (“rising tide”), except for TexAQS2k

11. Seasonal/Regional Aerosol Acidity Based on [SO4=/NO3-/NH4+] Slightly alkaline aerosol in fall and winter, as opposed to Yangtze sites. Different emission patterns, e.g. post-harvest burns at Yangtze: [K+]mean= 2.2 ±1.4 mg m-3. LP & WT closely neutralized, only occasionally alkaline, esp. ~9/5.

12. Summary • Positive vertical gradients of PM2.5 mass and sulfate point to atmospheric aerosol formation with the ground being a net sink, confirming Hendersonville observations • Localized plume on 8/30 carrying max [O3] at LaPorte, coincided with high [SO2] and showed max TOC increase relative to PM2.5 mass possibly indicating high aerosol forming potential • Average PM composition at LaPorte and Williams Tower are very similar, showing sulfate and organics each contributing ~1/3 to total fine mass • Insignificant regional differences in fine particle composition, but noticeable seasonal differences, esp. wrt C-species and sulfate, likely due to higher primary (SO2) emissions and photochemical activity in summer • Based on SO4=/NO3-/NH3+ system, PM2.5 in SE-US is slightly alkaline in winter but more acidic in summer • Significantly (~3x) lower PM2.5 mass in SE-US compared to Yangtze Delta region, which has a potential impact on American continent due to long-range transport across Pacific • Use of OOE factor 1.4 possibly too low for Houston aerosol; different factors might have to be applied for OC from quartz and XAD coated quartz backup filters due to different volatilities, which has been shown to be valid for the Atlanta Supersite data

13. PCM

14. La Porte Wind Rosesday = 0901-1900 CST, night = 1901-0900CST SO2 points to possible point sources to W and NW Daytime sea breeze dominated with prevailing SE flows. Those SE air masses were low in primary gaseous pollutants. Highest average Ozone with flows from SW and N. Photochemical precursors moved in from N and NW; with nighttime levels >> daytime indicating BL dynamics.