Heterogeneous impact of dust on tropospheric ozone: Sensitivity to season, species, and uptake rates

Heterogeneous chemistry on mineral dust particles causes significant reductions in important tropospheric trace gases such as O3, OH, and HNO3 in dust-dominated regions such as the North African Tropical Atlantic region. We analyze the spatial and temporal modes of dust-induced heterogeneous ozone removal (∆HO3) using empirical orthogonal functions (EOFs) and principal components analysis. We use the results to attribute ozone removal to specific pathways, and to assess the sensitivity of ozone removal to uncertainties in key heterogeneous uptake rates. The first EOF mode dominates ∆HO3 variance (93%) and shows that dust reduces O3 through heterogeneous reactions globally and year-around with the maximum in July. The second mode explains only 4% of ∆HO3 spatial variance yet accounts for most ∆HO3 seasonality. With base-value uptake coefficients, indirect ozone reduction due to HNO3 uptake exceeds direct heterogeneous uptake of O3. However, uncertainties in uptake rates allow the possibility that direct O3 uptake exceeds HNO3-induced O3 uptake, especially in Northern Spring. Recently published HNO3 uptake coefficients on authentic dust range from 10−5 < γHNO3 < 0.2, and imply that dust destroys 0.5–5.2% of tropospheric O3, respectively. Improved γHNO3 measurements and correct model representation of global dust composition, deliquesence, and aging are required to further reduce these order-of-magnitude uncertainties.