Influence of precipitation scavenging on the PM2.5/PM10 ratio at the Kennedy locality of Bogota, Colombia

Objective: To establish whether the scavenging effect reduces the PM 2.5 /PM 10 ratio in rainy periods in comparison with dry periods, at the Kennedy locality of Bogota, Colombia. Materials and methods: Relationships among hourly and daily PM 10 , PM 2.5 , PM 2.5 /PM 10 ratio, temperature, relative humidity and precipitation records from the Kennedy air quality station between January 2007 until September 2011 were analyzed. Results: The hourly mean PM 2.5 /PM 10 ratio was 0.36 (SD= ± 0.12), with an hourly maximum of 0.96. In rainy hours, the PM 2.5 /PM 10 ratio was 0.41 (SD= ± 0.13) and was reduced to 0.36 (DE= ± 0.12) in dry hours. On the other hand, the daily mean PM 2.5 /PM 10 ratio was 0.36 (SD= ± 0.09) with a daily maximum of 0.79. The daily mean on rainy days was higher (0.39; SD= ± 0.09) than that recorded on dry days (0.34; SD= ±0.08). All these differences were statistically significant. Conclusions: Precipitation reduces PM 2.5 concentrations at a lower extent than it reduces PM 10 concentrations. The analysis was not conclusive about the effect of precipitation on PM 2.5 concentrations, so it is not possible to assert that precipitation reduces the risk associated with the exposure to airborne particulate matter. To deepen our knowledge about the effect of precipitation on particulate matter pollution, it is recommended to apply additional techniques such as particle counting and particulate matter chemical characterization.