Wednesday, July 1, 2015

Great Salt Lake Summer Ozone Study: Ozone and Wind Roses

NEW Ozone/Wind Rose Interface! Click Here

A wind rose is a type of diagram that shows the distribution of wind direction at a location. Lines point from the direction the wind blows. Longer lines indicate that winds blow more frequently from that direction (given in a percentage of observations). Colors indicate the distribution of wind speed for that direction. For example, winds at Hawthorne in June 2015 were generally from the northwest or between south and east. Winds from the northeast or southwest were rare. Wind speed is almost always less than 4 m/s from any direction.
  wspd_legend Instead of plotting wind speed as a function of wind direction, we can plot ozone concentration as a function of wind direction. These are sometimes called a "pollution rose." The pollution rose below shows the same June 2015 period at Hawthorne. During the month of June, Hawthorne most frequently experienced unhealthy ozone concentrations when with winds were from the northwest. Air quality was generally good when winds blew from between south and east.
  plot_ozone_rose_ozone_qhw ozone_legend

 Figures like this can be created using the interface here:   

Options include:
  • Station ID: Select one in-situ station from the list of IDs
  • Rose Type: Select rose type. Ozone and Wind Speed have been discussed. (The clock roses will be discussed later.)
  • Time Option: UTC or Local time
  • Hour Interval: Default is "All Day" which shows all ozone observations between the dates. You can change the hour interval to look at 3 hour chunks of the day. This is useful to see ozone concentrations for different times of the day. For example, at Hawthorne pollution roses between 6:00-9:00 AM looks very different than at 3:00-6:00 PM
  • qhw_6-9qhw_12-18
  • Pot Range: This allows you to zoom in and out of the polar plot. The number selected will be the outermost percentage displayed.
  • Begin Time: The beginning month, day, year, and hour.
  • End Time: The ending month, day, year, and hour.
NOTE: The pollution rose currently bins the ozone concentration with the wind direction observed at the time the ozone measurement is recorded. This means that ozone monitors that record 1-hour ozone may have a wind direction that is different than the 1-hour average wind direction (does that make sense??)
---- Some examples ----
This tool allows you to look at ozone concentrations and wind for different days at any station. Pollution roses for Hawthorne on each day of IOP 1 were quite different. On Wednesday, the air was clean when air blew from the south, and was dirty when it blew from the north-northwest. Thursday, however, had much more frequent winds from the south and south east with cleaner air.
  qhw_IOP1_17 qhw_IOP1_18  
---- Another View Point ----
Rather than plotting ozone concentration or wind speed frequency as a function of wind direction, another way to look at ozone concentration is as a function of time of day. I call this an "ozone clock." Imagine looking at a 24-hour clock with midnight at the top and noon at the bottom. Below shows the MTMET "ozone clock" for the month of June. As expected, ozone concentrations are most healthy (green) in the morning hours. The afternoon, especially 15:00, most frequently has the most polluted air because ozone is produced in the presence of sunlight.
 NOTE: When creating plots like this for other stations, it is best to look at long periods of time (weeks to months), otherwise it may look as if a big bite has been taken out of the clock. The bit is caused when some hours have no wind direction reported. Ideally, the "clock" should roughly look like a circle because there are the same amount of each hour in a day (i.e. 3:00 AM occurs seven times in a week, as does 8:00 PM. In other words, each hour should occur 4.2% of the time). A wavy circle is caused when there are different amounts of observations for each hour during the period.   

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