Blowin in the Wind

During the past week, it has become evident that PM2.5 concentrations are significantly influenced by local meteorological conditions. This isn't a very ingenious comment, considering EVERYTHING suspended in the atmosphere is influenced by meteorological conditions. With this in mind, I guess it's still neat to prove that everything is right with the world and science is still behaving as it should.

So, lets provide example number 1. Late last week, after my return from Gulfport, I noticed these two distinct spikes in PM2.5 concentrations that occurred overnight (Figure 1).


Figure 1: PM2.5 concentrations

These brief increases are almost a full order of magnitude greater than the expected trend set earlier in the day. Clearly, a plume of something was advected (meteorology lingo for blown with the wind) over the instrument causing the higher readings. Had this been a poisonous gas (such as chlorine) the impacts on human life would have been huge. This plume, however, is still something that I would not want to be breathing in. Taking a look at wind data from this time, it is clear that a wind shift played a signifcant role in these higher readings. Figure 2 shows recorded 10 meter wind directions during this time.


Figure 2: Wind direction

At approximately 23:00, the wind changed direction from 50 degrees (from the NE) to 250 degrees (from the WSW). This change in wind direction lines up perfectly with the increased PM2.5 concentrations. This simple example provides clear evidence that small, microscale changes in the environment can produce significant changes in atmospheric pollutants.

The previous example was from a calm night, so your next question should be: What happens during an extremly unstable period, such as during the passage of a thunderstorm? No worries, I have diligently analyzed that situation also!

On the afternoon of June 28th, multiple thunderstorms passed through the area and provided some interesting data. Figure 3 below shows the changes in temperature and wind speed as the thunderstorms moved by.



Figure 3: Temperature and Wind Speed during the passage of thunderstorms.

The thunderstorm passages can be clearly seen when looking at the temperature data because of the sudden drops. When thunderstorms pass, they are accompanied by a pool of cold air that is immediately felt at the onset. Of course, wind speed is bound to increase during the thunderstorm, and this is also evident in the above figure.

So, what do you think the PM2.5 concentrations looked like during this time? The answer lies below!



Clearly, during the two main thunderstorm passages (at 13:30 and 17:30) PM concentrations fell dramatically. Thunderstorms get their energy by sucking air from the entire boundary layer (the lowest kilometer of the atmosphere) and using this air as fuel. Therefore, any pollutants at the surface are immediately taken into the thunderstorm and advected elsewhere/dissolved in precipiation.

TA DA!

The amazing effects of local weather conditions on the dispersion/advection of atmospheric particles!

In the wise words of Bob Dylan, "The answer, my friend, is blowin in the wind."