# How May Building Morphology Influence Pedestrians' Exposure to PM2.5?
## 2 Materials and Methods
### Data Preparation
#### 2.3.2 Building Morphology  
Building morphological parameters included building coverage ratio (ratio of the area occupied by buildings to total buffer area), mean building area, number of buildings, the average distance between nearest-neighbor buildings, and mean building height. All these parameters could affect pollution dispersion [12; 13]. Additionally, [PERSON] et al. [3] considered frontal area index and sky view factor to model PM2.5 and PM10. Both these factors were  
Figure 4: The Flowchart for data preparation.  
related to openness. They found that the frontal area index, representing building area in the direction of wind, played an important role in determining PM2.5 concentration. However, since this study already considered openness in the direction of the wind (see directional viewsheds in the next section), the frontal area index was excluded from the analysis.  
This study assumed that the 100-m buffer around each 50-m road-segment, covering an area of 41,394 m\({}^{2}\)(equivalent to approximately eight American football fields) was sufficient to study the effect of buildings' morphology on PM2.5 in 50-m road-segments. Therefore, buffers of 100 m around each 50-m segment delineated the proximity around roads to extract buildings' characteristics for calculating morphological parameters.  
Depending on the spatial relation of buildings with the 100 m buffer, we categorized buildings into three classes:  
1. Buildings with their centroid falling within the buffer
2. Part of the building/buildings intersecting with the buffer
3. Buildings within or touching the buffer  
Figure 5 depicts buildings in all three classes highlighted in orange used to compute various morphological measures of the buildings in relation to a 100-m buffer around each 50-m road-segment. Buildings with their centroid falling within the buffer (class 1) were used to compute mean building height, mean building area, and the number of buildings per 1000 m\({}^{2}\). This was to avoid considering the buildings with only a small portion in the buffer. In order to compute the building coverage ratio, this study considered the portions of the building intersecting with the buffer (class 2). Furthermore, to determine the average nearest-neighbor distance between buildings in the buffer, this study considered all the buildings either within the buffer or touching the buffer (class 3), as a partial account of buildings would not reflect the true distance between them. Table 1 provides the relevance and computation of each of these parameters:  
Table 2 summarizes the building morphological characteristics along the data collection paths. Among all the paths, the building coverage ratios of paths A and E were smaller. Many small buildings surrounded path A. In contrast, a few bigger and taller buildings surrounded path E. Path C had the largest site coverage ratio, followed by path D, and followed by path B. Still, on average, buildings around paths C and D were bigger in size, taller in height, and fewer in number compared to path B. In short, path A constituted smaller, shorter, and denser buildings with intermediate building coverage. Path B consisted of moderately dense, medium-sized buildings with median height and median building coverage. Path C was composed of relatively low-density, large-sized, and taller buildings but had the highest building coverage. Path D contained the largest  
Figure 5: Buffer and buildings used in building morphology calculation. The orange color indicates that the buildings or their parts meet criteria for specified class (class 1, 2 or 3).  
sized low-density and distantly placed buildings with medium height and relatively high building coverage. Finally, path E was surrounded by small-sized, sparsely placed and short buildings. Path E also had the lowest building coverage among all paths.