Introduction: Chronic exposure to particulate matter air pollution has a significant effect on respiratory health and cardiovascular system. Information on the relationship between levels of particulate matter smaller than 2.5μm () and mortality rates in Ethiopia is lacking in Ethiopia involving a growing City like Addis Ababa.

Objectives: The main objective of the study was to investigate the relationship between  concentrations and daily mortality rates associated with respiratory and cardiovascular mortality in Addis Ababa, Ethiopia.

Methods: We followed a three years’ time series study design to collect information on daily level of air pollution and hospital-based mortalities. Data on the daily averaged  concentrations were obtained from Beta Attenuator Monitor (BAM 1022). The daily mortality counts were obtained from six public hospitals in Addis Ababa. A Poisson regression with a generalized additive model (GAM) adjusted for Ambient Temperature (AT) and Relative Humidity (RH) was performed to assess the relationship between  concentrations and daily mortality rates.

Results: concentration levels were significantly associated with both all cause and cause-specific deaths.  For all-cause mortality, the effect of PM_2.5 was statistically significant for most of the lags studied. For cardiovascular and respiratory mortality, significant effects were observed at lag 3 and lag 4 respectively.

Conclusions: PM_2.5 was significantly associated with both respiratory and cardiovascular mortality in Addis Ababa, Ethiopia. Preventive measures to reduce the level of air pollution is highly advised.

Key Words:  BAM; PM_2.5; Daily mortality; generalized additive model