Transcript Lesson06
METO 621 CHEM Lesson 6 A Typical Day in a Pollution Episode •A common severe pollution weather pattern occurs when high pressure is centered just west of the Mid Atlantic region. H •Circulation around the high pressure center moves pollution from points west into the mid-Atlantic. Fort Meade profile 6/19/2001 After Sunrise Ozone Levels Increase Sharply Sub. inv. Altitude • The ground heats up and the warm air above it erodes the inversion. • Ozone and other compounds above the inversion layer mix with the pollution under the layer. • This causes a dramatic increase in ground-level ozone, beginning around 10 AM. Noct. inv. Temperature Ozone Levels Reach a Maximum in the Afternoon Sub. inv. Altitude Altitude Sub. inv. Noct. inv. Temperature Temperature • If the weather remains the same, the temperature inversion forms again after dark. • Ozone concentrations above the inversion remain at a constant, relatively, high level. • Ozone trapped under the inversion reacts with other pollutants, and the surface; the ozone concentration diminishes. Altitude After Sunset Ozone concentration remaining constant Ozone concentration diminishing Temperature Temperature Inversion Daily Ozone Cycle Ozone production follows a daily cycle with maximum concentrations typically observed in the late afternoon. Ozone Concentration Sunrise Sunset Time of day This cycle is a signatu of the dynamic processes of atmospheric air pollution Comparison of ozone data at Fort Meade for August 2 and 8 2002 Overplot of 2 and 8 Aug 2002 and the difference between the two days Difference 2 Aug minus 8 Aug*1.2 Comparison of Aug 2 and 8, 2002 • Ozone data for August 8 is typical for local pollution on a clear warm day. • The NOx and VOC are emitted early in the morning and the ozone amount slowly increases as the temperature increases. The peak production is at about 3-4 in the afternoon when the temperature at the ground is a maximum. • The back trajectory shows fast upper level winds, which start at a high altitude and then subside to boundary levels at Baltimore. • Small probability of upper air being polluted. Comparison of Aug 2 and 8, 2002 • On the 2nd of August the back trajectories show that the air is moving slowly at the boundary layer, and the probability of this air being polluted is high. • The nocturnal inversion typically breaks down at about 10-11 in the morning. • Hence the peak in ozone at this time must come from downward transport. • The overall shape of the ozone data on Aug 2 is a combination of locally produced ozone peaking at about 3 pm and a downward movement of ozone from above at about 10.00 am. • This ozone above the boundary layer is yesterday’s ozone • The winds above the boundary layer are usually high. Hence the ozone has been transported some distance Westerly transport is often present when the highest ozone is observed in the mid-Atlantic. 24 hr. Back-trajectories on days of 1-hr. ozone exceedances from 1997 through 2002, Baltimore area Aircraft measurements of ozone Aircraft measurements of Sulfur Dioxide Lee Side Trough Upper level winds from the west… …are turned by the lee side trough daytime Low Level Jet Air pollution from the southwest… …comes into Maryland overnight nighttime Plot of low-level winds from the Fort Meade, MD wind profiler during a high ozone episode LLJ LLJ LLJ Rapid Update Cycle (RUC) model depiction of the LLJ during a high 9:00 PM ozone period (high wind speeds in red). 03:00 AM 11:00 PM 01:00 AM 05:00 AM 07:00 AM Modes of Transport All three modes of transport are important when the highest pollution values are observed in the mid-Atlantic. •Large scale ~ 800 km (~70-100 ppbv) (Much of the Eastern US) •Medium scale ~ 200- 800 km (Carolinas to New England Region) •Small scale ~ 100 km (N. Virginia to Baltimore, Research Triangle to NC/VA border) Sources • Different types of transport imply different types of sources – Local transport Cars, industry, and other sources in the local area – Long distance transport Primarily power plants to W, though plumes from cities certainly contribute. – Low level jet Primarily cars and other low level sources; moves from SW to NE How Significant? • On the mid-Atlantic’s worst ozone days, a significant amount of pollution comes from long distance transport originating in upwind states. • UMD Aircraft measure levels as high as 110 ppbv floating in from the west Effects of the August 15, 2003 Blackout on Air Quality Selinsgrove, PA Coming soon to GRL Compared with Aug 4, 2002 Effects of the 2003 Blackout on Air Quality CEM data indicate reductions of 60-80% L. Marufu, B. Taubman, B. Doddridge et al. Effects of the 2003 Blackout on Air Quality In summary • • • • • It isn’t all transport… It isn’t all local… It isn’t all power plants… It isn’t all automobiles… The problem will not be solved by addressing any one of these problems individually. ALL of these will have to show significant reductions for us to breathe clean air.