Effects of olive tree branches burning emissions on PM2.5 concentrations

•Burning of olive tree branches is a major air pollution source.•It increases average fine PM levels by more than a factor of 2.•Effect is maximum during the most polluted periods.

An olive tree branches burning emission inventory for Greece is developed based on recently measured emission factors and the spatial distribution of olive trees. A three-dimensional chemical transport model (CTM), PMCAMx, is used to estimate the corresponding impact on PM2.5 concentrations during a typical winter period. Assuming that burning of olive tree branches takes place only during days with low wind speed and without precipitation, the contribution of olive tree branches burning emissions on PM2.5 levels is more significant during the most polluted days. Increases of hourly PM2.5 exceeding 50% and locally reaching up to 150% in Crete are predicted during the most polluted periods. On a monthly-average basis, the corresponding emissions are predicted to increase PM2.5 levels up to 1.5 μg m−3 (20%) in Crete and Peloponnese, where the largest fraction of olive trees is located, and by 0.4 μg m−3 (5%) on average over Greece. OA and EC levels increase by 20% and 13% respectively on average over Greece, and up to 70% in Crete. The magnitude of the effect is quite sensitive to burning practices. Assuming that burning of olive tree branches takes place during all days results in a smaller effect of burning on PM2.5 levels (9% increase instead of 20%). These results suggest that this type of agricultural waste burning is a major source of particulate pollution in the Mediterranean countries where this practice is prevalent during winter.