 |
| Fig 1 :Sunset in Bondville IL |
Links to various air quality and meteorology monitoring at Bondville can be found here : Summer Air quality Campaign 2013-2014
Introduction
Air quality in the Midwest is unique from Eastern or Western or Southern US. Midwest has a mix of some big urban population like Chicago, St louis, Kansas City, Indianapolis and is home to one of the most intensive agriculture rural centre. Therefore the chemistry of air pollutants such as particulate matter is different.
The state of air quality across the United States is measured by key pollutants, also referred to as criteria pollutants. One of the common and widely measured pollutants in PM2.5 (particle less than 2.5 micron in aerodynamic diameter). US EPA has a set a guideline for the all these criteria pollutant including PM2.5. The guideline value is 35 ug/m3 for a period of 24 hr. Concentration of PM2.5 in Bondville, IL is variable through out the year, but remain under 35 for most time period. [to be conti]
Random Post 1 : Effect of Wildfires, high temperature and humidity in Sept. 2013
High temperature and humidity causes high particle mass concentration in September 10 2013. Image from MODIS Satellite is shown below. The grey is the cloud cover across US. however the blue to red scale is reflection captured by the satellite. the thicker the air layer [ thickness is due to high particle mass or number in the atmosphere, therefore will be shown by the red color in the image below].
 |
| Fig 2. : MODIS AOD on Sept. 2013 [http://alg.umbc.edu/usaq/archives/2013_09.html] |
 |
| Fig. 3 :Air Quality Index (AQI) for Sept 10 2013: The AQI is based on concentration of PM2.5 or Ozone [airnow.org] |
North Eastern US and Southern-Midwestern states such as Texas, Kansas, Oklahoma have been experiencing huge forest fire. The high particulate mass in the picture is largely due to these fires and you can see that the fire plume is moving north and eastward. Air Quality index is used by US EPA to determine the quality of air. Yellow indicate moderate air quality which imply that long term exposure may cause some health problems such as irritation.
Local meteorology and air pollution on Sept 2nd week 2013
As already stated this week are characterized by high temperature (~ 90 F, figure 4 top left panel) and high humidity condition >70 % during the day. Low pressure system was over the great lakes region, and Rh lift index ( bottom right in figure 4 of <-5 ) indicates condition were favorable for thunderstorm as well. Figure 5 is a surface meteorology for Sept. 10 which shows a stationary front over the Midwest, winds from S/SW at a 5-8 m/s and scattered cloud for most day.
 |
Figure 4 : Regional upper surface map , from http://weather.unisys.com/archive/eta_init/1309/13091012.gif
The fronts in figure 5 are indicated by the thick blue-red line. a mixed blue-red line indicates a stationary front. |
 |
| Figure 5 : Surface meteorology, http://weather.unisys.com/archive/sfc_map/1309/13091012.gif |
Air pollution
-particle number concentration [10nm to 500 nm]
particle number and their size changes with the different sources of pollutants and meteorology. Figure 6 below is a color plot that shows time on the x-axis, particle diameter on the left y axis and concentration per cm3 on the color scale on the right y-axis. From this figure, we can see that there is a strong early morning concentration of particle from 10 to ~90 nm. This seems to last till the noon hours.
-Gas measurements such as Sulphur dioxide (So2) and Ozone(O3)
For the same day, figure 7 shows SO2 concentration and the high particle concentration event co-insides with the increase in SO2 concentration. Sulphur dioxide can come from various sources such as industries, and vehicles. Wind direction (not shown here) during this morning to noon period were coming from SW-S. O3 continues to record relatively higher concentration ~ 68 ppb @ 11:00 am CDT (Fig. 8). The trend in O3 high correlates well with the incoming solar radiation which also peaks at the same time to 756.7 watts/m2. During the same time period, elevated levels of NOY ( it is a sum of NOx [NO and NO2] plus Nitric acid[oxidation product of NOx] )
 |
| Figure 6: U of Iowa aerosol campaign 2013/14 |
 |
| Figure 7 : U of Iowa 2013/14 aerosol campaign |
 |
Figure 8 : Time series of O3 from Sept 9 to 10 2013-( source : NCORE EPA )
Particle formation in the atmosphere in early March 2014
Particle formation or nucleation is a common phenomenon observed in the atmosphere. The physical basis of nucleation is the condensation of gas molecules into a stable cluster ( ~1-2 nm in size) which eventually grows or dis-integrates. If this cluster growth dominate the dis-integration, then it will eventually grows into larger size as particle. Current instrumentation on particle couldn't detect particles below 2.5 nm , so the dynamics ( at least in terms of its number) of these clusters is still under exploration. Of the various trace gas vapour available in the atmopshere, the early cluster formation is dominated by water vapor and sulphuric acid, likely because they can easily change the phase from gas to liquid. however for the growth of cluster to larger sizes, the contribution of other trace gases such as ammonia, amine, volatile organics such as isoprene etc, play important role. Because the concentration of these trace gases depends vary with location, nucleation or particle formation events around the world have different characteristics in terms of growth rate of these cluster, number of these particles, and also particle chemistry.
During our field campaign we saw numerous particle formation events. Shown in the figure below is a particle formation event seen in March 2014. Particle formation event correlates well with the increase in the sulphur dioxide which indicate the crucial role played by So2. However during our field we saw particle formation associated with a wide range of sulphur concentration ranging from 1 ppb to >5 ppb. March nucleation events are mostly associated with So2 concentration around ....
|
