Question about modeling RLINE with near-road receptors (Solved)

Happy New Year!

I get a question when modeling traffic-related PM2.5 using RLINE. In the result, the modeled concentrations of traffic-related PM2.5 is maybe too low for some receptors placed within 20 meters away from major roads (Figure 1).

Figure 1. The X axis is the logged distance to major road (meters). Y axis is the annual average of modeled concentrations of traffic-related PM2.5 (µg/m3). I circled those results with abnormally low values.

After that, I’m wondering if there is a buffer limit that we should model the concentrations of traffic-related air pollution outside of that buffering area. As mentioned by the [technique document](file:///C:/Users/zhangx24/Downloads/RLIN_MODELDESCRIPTION_5-23-13.PDF) of RLINE, the RLINE results yield to great uncertainties if receptors are placed too close to sources (although the developer added an algorithm to adjust this issue). Then I tested the RLINE using a fake road source and a series of receptors with different distances to the source road. The “dCL” in the source file was set to 0. The meteorology input is from one of the example studies. The hourly result show that:

  1. The variation of modeled concentrations decreases with distance to road.
  2. For each hour’s result, receptors being close to the road or on the road doesn’t necessarily to have higher concentrations.
  3. The differences of results between near-road receptors and other receptors varied by the input of road sources.

Here is my fake road source input:
Source input file
Group X_b Y_b Z_b X_e Y_e Z_e dCL sigmaz0 #lanes Emis Hw1 dw1 Hw2 dw2 Depth Wtop Wbottom
RFS -100 0 1 100 0 1 0 2 1 1 0 0 0 0 0 0 0

And here are the receptors:
**This file contains receptor locations **
X_coordinate Y_Coordinate Z_Coordinate
**---------------------------------------------- **
0.0 0.0 1
0.0 0.2 1
0.0 0.5 1
0.0 0.7 1
0.0 1.0 1
0.0 1.2 1
0.0 2.0 1
0.0 3.0 1
0.0 5.0 1
0.0 10.0 1
0.0 15.0 1
0.0 20.0 1
0.0 30 1
0.0 40 1
0.0 50 1

Overall, I have a concern about to run RLINE with receptors that placed extremely close to road sources. I’m wondering if it is the normal setting of RLINE? Maybe those on-road or near-road receptors have lower concentrations in the real world situation?

Those texts and figures are prepared in a short time. I apologize for any typos or errors on them.

Feel free to let me know your thoughts!