Bioaerosol size as a potential determinant of airborne E. coli viability under ultraviolet germicidal irradiation and ozone disinfection

Abstract

Abstract Ultraviolet germicidal irradiation (UVGI) and ozone disinfection are crucial methods for mitigating the airborne transmission of pathogenic microorganisms in high-risk settings, particularly with the emergence of respiratory viral pathogens such as SARS-CoV-2 and avian influenza viruses. This study quantitatively investigates the influence of UVGI and ozone on the viability of E. coli in bioaerosols, with a particular focus on how E. coli viability depends on the size of the bioaerosols, a critical factor that determines deposition patterns within the human respiratory system and the evolution of bioaerosols in indoor environments. This study used a controlled small-scale laboratory chamber where E. coli suspensions were aerosolized and subjected to varying levels of UVGI and ozone levels throughout the exposure time (2–6 s). The normalized viability of E. coli was found to be significantly reduced by UVGI (60–240 μW s cm−2) as the exposure time increased from 2 to 6 s, and the most substantial reduction of E. coli normalized viability was observed when UVGI and ozone (65–131 ppb) were used in combination. We also found that UVGI reduced the normalized viability of E. coli in bioaerosols more significantly with smaller sizes (0.25–0.5 μm) than with larger sizes (0.5–2.5 μm). However, when combining UVGI and ozone, the normalized viability was higher for smaller particle sizes than for the larger ones. The findings provide insights into the development of effective UVGI disinfection engineering methods to control the spread of pathogenic microorganisms in high-risk environments. By understanding the influence of the viability of microorganisms in various bioaerosol sizes, we can optimize UVGI and ozone techniques to reduce the potential risk of airborne transmission of pathogens.