Aerosol and Meteorological Patterns During the July 1995 Episode

1. Aerosol and Meteorological Patterns During the July 1995 Episode Models3 Evaluation Project. CAPITA June 18 2000

2. Surface Visibility Data

3. Noon Weather Filtered Bext

4. Noon Weather Filtered Bext

5. Bext Diurnal Cycle – 7/15/95 • Relative humidity follows a pronounced diurnal cycle. In the Eastern US during the summer the RH is ~90% in the morning and evenings and ~60% in the mid afternoon. • This causes a significant diurnal cycle of aerosol extinction coefficient, the highest values occurring in the early morning hours

6. Airmass transport

7. July 1995 Episode Meteorology

8. Summary of the Bext and Meteorology during 1995 Aerosol Episode • The 1995 episode extended for ten days from July 08 through July 18. • Prior to the episode a swift Canadian airmass descended over most of the northern and central Eastern US.resulting in low aerosol concentrations throughout the domain, particularly in the north. • Between July 8 and 12 Canadian airmass stagnated over Iowa - Ohio and the aerosol extinction coefficient increased to over 0.3 km-1 at a number monitors in the Midwest. • During the next four days, the airmass meandered over the Midwest and the aerosol levels increased further peaking on July 13-15. • The transport then shifted to stronger persistent flow to the east and aerosol concentrations in the Midwest fell with decreases occurring in western part of the Midwest first. • By July 18, only the Eastern Atlantic states had elevated aerosol levels. • The diurnal cycle of RH causes a significant diurnal cycle of aerosol extinction coefficient, the highest values occurring in the early morning hours • The July 95 aerosol episode was not particularly intensive compared to other episodes in the summer of 1995.

9. Comparison of Bext and PM2.5 Concentrations

10. Monitoring data for PM2.5 and Chemical Species

11. PM 10 Concentration

12. PM2.5 Concentration

13. Sulfate Concentration