# Bacterial Aerosol in Ambient Air--A Review Study
## 3 Discussion
### Interactions with Air Pollutants  
3.1.1. Particulate Matter (PM\({}_{1}\), PM\({}_{2.5}\), and PM\({}_{10}\))  
Particulate matter generally shows strong positive correlations with total bacterial concentrations (Figure 2). Across a wide range of suspended dust concentrations, from a few to over 300 \(\upmu\)g/m\({}^{3}\), both positive and negative correlations between bacterial aerosols and particulate matter have been observed. Only one study, conducted by [PERSON] et al. [49], evaluated the relationship between bioaerosol concentrations and submicron particles. In this study, PM\({}_{1}\) (ranging from 68 to 120 \(\upmu\)g/m\({}^{3}\)) exhibited a significant positive correlation (\(R=0.60\), \(p<0.05\)). PM\({}_{2.5}\) exhibits even stronger correlations with bacterial aerosols across multiple studies, with coefficients as high as 0.808 (\(p<0.01\)) [62] and 0.652 (\(p<0.01\)) [24]. The highest positive correlation was observed at higher PM\({}_{2.5}\) concentrations, ranging from 31.3 to 214.7 \(\upmu\)g/m\({}^{3}\), and bacterial aerosol concentrations ranged from 497.7 to 1736.5 CFU/m\({}^{3}\). In comparison, measurements of PM\({}_{1}\), PM\({}_{2.5}\), and PM\({}_{10}\) conducted in India during the monsoon, post-monsoon, winter, and summer seasons [49] revealed the highest correlation coefficient with PM\({}_{10}\) at 0.75 (\(p<0.05\)) for PM\({}_{10}\) concentrations ranging from 29 to 315 \(\upmu\)g/m\({}^{3}\) and very high bacterial concentrations (4595 \(\pm\) 3410 CFU/m\({}^{3}\)). The lowest correlation was observed with PM\({}_{2.5}\) at 0.55 (\(p<0.05\)), suggesting that the bioaerosol loading in fine particulate fractions is lower compared to larger fractions. [PERSON] et al. [49] emphasized the elevated microbial contribution in larger-sized particles. [PERSON] [71] and [PERSON] et al. [72] explained that larger particles tend to have higher bacterial concentrations due to their greater surface area and volume, which can harbor microbial cells. As particle size decreases (i.e., aerodynamic diameter becomes smaller), bacteria are more likely to remain suspended in the air as individual cells rather than attached to particles. Smaller particles can remain airborne longer and more easily, allowing microbes to be suspended as single cells. Interestingly, PM\({}_{2.5}\) displays seasonal variations, with a positive but not statistically significant correlation in autumn (0.139) and a negative correlation in winter (\(R=-0.491\), \(p<0.05\)) [47]. The significant negative correlation during winter is consistent with findings  
Figure 2: Graphical summary of statistically significant correlation between bacterial aerosol and (a) PM\({}_{2.5}\) and (b) PM\({}_{10}\). from [PERSON] et al. [4]. [PERSON] et al. [43] noted that the increased concentration of PM\({}_{2.5}\) during winter, due to phenomena such as thermal inversion and fog, can elevate bioaerosol levels. However, their observations did not identify a statistically significant positive correlation between PM\({}_{2.5}\) and bioaerosol levels during this season. This suggests that, although higher PM\({}_{2.5}\) levels in winter may be associated with factors that could potentially influence bioaerosol concentrations, the data do not support a significant increase in bioaerosols. [PERSON] et al. [64] also did not find a statistically significant relationship between the total number of bacteria and the levels of PM\({}_{2.5}\) and PM\({}_{10}\). They suggested that this lack of correlation may be related to low air temperatures during sampling, which negatively affected the survival of microorganisms. In contrast, during spring (March 2018-2023), correlations slightly fluctuated, with values of 0.77 in the pre-COVID-19 period, 0.60 during COVID-19, and 0.67 post-COVID-19 [65]. Similar to fine particles, the correlations between coarse particles and bacterial aerosols vary across studies, reflecting different contexts, conditions, and potentially geographic or methodological differences.