DFW Conceptual Model Review

Transcription

1 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 1 DFW Conceptual Model Review Presented at Dallas-Fort Worth Nonattainment Area Air Quality Technical Meeting June 16, 2014

2 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 2 The Purpose of a Conceptual Model Ozone formation Conceptual Models characterize ozone trends, precursors, formation and transport in a particular geographic area, to explain the dynamics of ozone formation in that area. Conceptual Models are required by the US Environmental Protection Agency (US EPA) to accompany photochemical modeling performed for the state implementation plans (SIP). The Conceptual Model document will be an appendix in the proposed and adopted DFW Eight-Hour Attainment Demonstration SIP revision. More that 50 scientific and technical papers are referenced and used to develop the DFW Conceptual Model.

3 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 3 Topics: Conceptual Model Results Trends for Ozone, Oxides of Nitrogen (NO X ) and Carbon Monoxide (CO) Weekday/Weekend Effect for Ozone, CO and NO X Limitation Ratios Meteorology Effect on Ozone Case Study

4 Monitors in the DFW Area Denton is the current Design Setting Monitor at 78 ppb (as of June 11, 2014) Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 4

5 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 5 Ozone Design Values and Population in the DFW Area 1-Hour 8-Hour Ozone Design Values have been trending downward for several decades, while population has been increasing. Increased population corresponds to more emissions from automobiles, area sources, electric power generation, etc.

6 DFW Number of Days Eight Hour Ozone Maximum Greater than 75 ppb Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 6 The number of days with ozone monitored above 75 ppb has decreased over time. The variation in the frequency is greatly affected by meteorology, and thus, the frequency statistic is not very stable, which is why there are large jumps occur from year to year. *Includes all Counties with monitors in the DFW air quality planning area (+Navarro, Hunt & Hood).

7 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 7 Days with Eight-Hour Ozone Greater Than 75 ppb by Day of the Week When comparing Sundays to Wednesdays, a weekday/weekend effect exists (statistically significant result Chi-square). Counts can vary greatly from year to year. Only includes counties from the designated non-attainment area

8 Ozone Season NO X Trends in DFW NO X concentrations show a decrease at the 90 th and 50 th (median) percentile. The 10 th percentile remains flat over the 17-year period. These trends combine all monitors in the DFW area. The peaks and valleys in the trend lines are most likely caused by changes in meteorology, such as wind speed and direction changes. These peaks and valleys are more pronounced in the 90 th percentile, because the statistic is more prone to vary than the median (50 th percentile). Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 8

9 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 9 DFW NO X 90 th Percentiles Trends March-October, Rural The blue line is the best fit trend line. Rural Rural Rural Dallas Hinton shows the greatest decrease in NO X and the highest concentrations. Rural The Parker County monitor has the lowest concentrations. Note that the trend-line decreases more at monitors in or near urban DFW. Since on-road is the largest source of NO X in DFW, particularly within the urban core, the decline in overall NO X is due primarily to ongoing fleet turnover reductions in on-road emissions from both gasoline and diesel vehicles.

10 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 10 Day of Week Daily Maximum NO X March-October The Boxplot suggest that a day-of-theweek effect exists in the DFW area for NOX. This day-of-the-week effect suggests that NOX is emitted in greater amounts during week days, and probably due to more automobile activity. These data are from March through October from years The red line is a reference of the median of all weekdays. Note the medians on Sunday and Saturday.

11 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 11 DFW Annual Mean Carbon Monoxide, CO concentrations from have been dropping. CO is a good tracer for gasoline vehicle activity. The intra-annual variation is most likely from meteorology and not on-road activity. CO does not have a weekday/weekend effect.

12 Oil and Gas Emissions Annual Geometric Mean of Ethane Using 24-hour Canisters Oil and Gas emissions are trending up at monitors near oil and gas activity. Other monitors are relatively flat. Ethane is used as a surrogate for oil and gas activity. Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 12

13 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 13 On-Road Emissions Annual Geometric Mean of Ethylene Using 24-hour Canisters On-road emissions are trending downward since Monitors near on-road activity observe higher concentrations. Ethylene is used as a surrogate for all on-road emissions.

14 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 14 VOC/NO X Ratio Trends VOC-limited means ozone cannot be created due to the lack of VOCs. NOX-limited means that ozone cannot be created due to the lack of NOX. Transitional is between NOX- and VOC-limited. Dallas Hinton and Fort Worth NW monitors show transitional. Areas outside of the urban core or rural areas show NOX-limited.

15 Where are the Ozone Design Values Set? Ozone Season Winds Highest Frequency Direction of wind on high ozone days Ozone Design Values have typically been set in the north and northwest part of the DFW area and follow the typical wind pattern in DFW (above). The location where the Design Values are set generally remains the same, but the intensity has dropped over time. Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 15

16 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 16 Wind Effect on Ozone Concentrations When ozone is below 75 ppb, the winds are more frequently from the south, and the speeds are higher. Note the oranges, reds and purples, denoting high wind speeds. High wind speeds dilute pollutants, and less ozone is created. Wind speed has a sizable influence on ozone production. Low Ozone Days When ozone is above 75 ppb, the winds contain more hours where wind speeds are lower. Note the more blues and greens, denoting slower wind speeds. Also, the wind directions are less organized (less from just one direction). This disorganization is a result of low wind speeds, which allows pollutants to accumulate and ozone to form. High Ozone Days

17 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 17 Case Study: August 31, 2013 Wind parcels accumulate pollutants, NO x, and ozone as they travel northward. Sunlight causes the pollutants to react and form ozone. It can take several hours for ozone precursors to react and form ozone and thus, the maximum concentration is usually miles downwind of the urban core or primary area of emissions. The location of where high ozone is recorded is driven by local wind patterns. This very typical example shows the trajectory the wind took starting at 7:00 AM and ending ten hours later at the Denton monitor at 17:00 (5:00 PM), the time of the highest one-hour ozone (one-hour at 93 ppb and eight-hour at 85 ppb). The trajectory the wind takes is from south to north, traversing urban DFW.

18 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 18 Case Study: August 12, 2010 Wind parcels accumulate pollutants, NO x, and ozone as they travel northeastward. Sunlight causes the pollutants to react and form ozone. It can take several hours for ozone precursors to react and form ozone and thus, the maximum concentration is usually miles downwind of the urban core or primary area of emissions. The location of where high ozone is recorded is driven by local wind patterns. The trajectory the wind takes is from south to northwest, traversing urban DFW. Keller observe 83 ppb eight-hour at 11:00 LST. Winds were calm hours before time of elevated ozone. This day also observed high temperature(103f), with plenty of sunlight for hours before and after time of peak ozone.

19 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 19 Concluding Remarks Ozone, NO X, and VOC are trending downward. CO is also trending downward. Although not an ozone precursor, it does show that automobile exhaust emissions are trending downward. The number of ozone exceedance days has dropped over time. The DFW air mass, in general, is trending towards NO X limited, although each monitor at each location has its own unique limitation ratio. The effect of meteorology on ozone cannot be overemphasized. Low wind speeds and sunshine can trigger a high ozone day, given the current emissions in the DFW area.

20 Air Quality Division DFW Conceptual Model Review June 16, 2014 Page 20 Contact Information Air Modeling and Data Analysis Section