Diurnal and seasonal variability of particulate matter concentrations over Kigali

Abstract

The measurement of atmospheric particulate matter of two distinct size <2.5 µm and <10µm was collected in Kigali since 2018 and as sample from Apr-2019 to March 2020 at air quality and climate change monitoring project located at Meteo Rwanda head quarter was used in this dissertation. This measurement has several purposes but, in this research, data was carried out with a purpose of analyzing the diurnal and seasonal variability in PM mass concentration within different seasons of the collected time and access the potential causes associated with this variation. The Environmental Protection Agence compliant TELEDYNE API, Model T640 Particulate Matter (PM) Mass Monitor was used in this research. Meteorological parameters are from Met-o Rwanda Kigali station where the instrument is installed. Complex factors determining the PM variability, relation between PM and meteorological parameters such as temperature, Relative Humidity, wind direction, wind speed and solar radiation was analyzed using statistical analysis techniques associated with tools available in Openair package of R language. The Atmosphere that is laden with dust due to occurrence of transported haze, the summer heating, traffic emissions in Kigali, PM from fossil fuel burning, forest fire from neighboring countries, other forms of combustion process either local or regional that reach the sampling site and the lack of air pollutants removal process (wet deposition/wash out and rainout) in the dry season (June July August and January February(JJA and JF) are observed to contribute to the higher PM mass concentration level. Two peaks (06:00 to 08:00 am and 6:00to 9:00 pm) of the evident diurnal cycle in all seasons was observed. The elevated temperature, favorable atmospheric diffusion conditions that could dilute the daytime aqueous particulates matter and particulate accumulation at low temperature during the night times phenomena resulted in higher level of PM mass concertation in the night times than the day times in all seasons. Back trajectories and wind rose demonstrated that some PM are from anthropogenic and traffic with a few transported hazes. An adoption of green city, moto vehicle inspection, use of quality fuel (gasoline and diesel) and the use of clean energy associated with more air quality monitoring sites in Kigali and countryside are recommended to keep our air clean