Mineral dust contains material such as TiO2 that is well known to have photocatalytic activity. In this laboratory study, mixed TiO2‐SiO2, Saharan dust and Arizona Test Dust were exposed to NO2 in a coated wall flow tube reactor. While uptake in the dark was negligible, photoenhanced uptake of NO2 was observed on all samples. For the mixed TiO2‐SiO2, the uptake coefficients increased with increasing TiO2 mass fraction, with BET uptake coefficients ranging from 0.12 to 1.9 × 10−6. HONO was observed from all samples, with varying yields, e.g., 80% for Saharan dust. Three‐dimensional modeling indicates that photochemistry of dust may reduce the NO2 level up to 37% and ozone up to 5% during a dust event in the free troposphere.

[1] The nitrate formation on dust particles is considered as a sink for atmospheric NO y (such as HNO 3 ). However mineral dust is shown here to be an effective photocatalyst for transformation of nitrate anions into NO and NO 2 , without involving its photolysis. The photodecomposition of NO 3 À at the surface of synthetic mineral dust samples of SiO 2 , TiO 2 , mixed TiO 2 -SiO 2 and authentic sand doped with 6% NO 3 À was studied by means of a flow-tube at 298 K with UVillumination in the 340 -420 nm range at relative humidities between 5 and 80%. Both NO and NO 2 are observed during irradiation of films composed of either mixed TiO 2 -SiO 2 , pure TiO 2 and authentic minerals from the Sahara. The relative humidity strongly affects the concentration of NO x released into the gas phase. The photoinduced nitrate conversion into NO x is discussed as being a potential renoxification process of the atmosphere.

The ozone decomposition onto mineral surfaces prepared with traces of solid TiO2 in a matrix of SiO2 in order to mimic mineral dust particles has been investigated using a coated-wall flow-tube system at room temperature and atmospheric pressure. The ozone uptake coefficients were measured both under dark conditions and irradiation using near UV-light. While uptake in the dark was negligible, a large photoenhanced ozone uptake was observed. For TiO2/SiO2 mixtures under irradiation, the uptake coefficients increased with increasing TiO2 mass fraction (from 1 to 3 wt %), and the corresponding uptake coefficient based on the geometric surfaces ranged from 3 x 10(-6) to 3 x 10(-5). The uptake kinetics was also observed to increase with decreasing ozone concentration between 290 and 50 ppbv. Relative humidity influenced the ozone uptake on the film, and a reduced ozone loss was observed for relative humidity above 30%. The experimental results suggest that under atmospherically relevant conditions the photochemistry of dust can represent an important sink of ozone inside the dust plume.

The heterogeneous reaction of NO(2) on Saharan sand collected from different locations has been studied at 298 K and 25% relative humidity using a horizontal coated-wall flow tube. The sand samples originated from Mauritania, Algeria, Morocco and Tunisia and were taken as simplified proxies for mineral dust. While the uptake in the dark was always very small, a photo-enhanced uptake of NO(2) was observed on all four samples showing that natural minerals do have a photochemical activity. The uptake coefficient gamma(BET) was measured for all sands. In the dark, the gamma(BET) values are (1.60 +/- 0.24) x 10(-8), (0.43 +/- 0.06) x 10(-8), (0.94 +/- 0.14) x 10(-8) and (0.59 +/- 0.09) x 10(-8) for the samples from Mauritania, Algeria, Morocco and Tunisia, respectively. Under realistic atmospheric conditions, the observed photo-enhancement leads to uptake coefficients of (1.46 +/- 0.21) x 10(-7), (0.35 + 0.05) x 10(-7), (1.30 +/- 0.19) x 10(-7) and (0.89 +/- 0.13) x 10(-7), respectively, i.e. an enhancement factor ranging from 8 to 15. This study shows that the photochemistry of natural minerals will impact significantly on the heterogeneous chemistry of NO(2).

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Genome-wide association studies for severe malaria (SM) have identified 30 genetic variants mostly located in non-coding regions. Here, we aimed to identify potential causal genetic variants located in these loci and demonstrate their functional activity. We systematically investigated the regulatory effect of the SNPs in linkage disequilibrium (LD) with the malaria-associated genetic variants. Annotating and prioritizing genetic variants led to the identification of a regulatory region containing five ATP2B4 SNPs in LD with rs10900585. We found significant associations between SM and rs10900585 and our candidate SNPs (rs11240734, rs1541252, rs1541253, rs1541254, and rs1541255) in a Senegalese population. Then, we demonstrated that both individual SNPs and the combination of SNPs had regulatory effects. Moreover, CRISPR/Cas9-mediated deletion of this region decreased ATP2B4 transcript and protein levels and increased Ca2+ intracellular concentration in the K562 cell line. Our data demonstrate that severe malaria-associated genetic variants alter the expression of ATP2B4 encoding a plasma membrane calcium-transporting ATPase 4 (PMCA4) expressed on red blood cells. Altering the activity of this regulatory element affects the risk of SM, likely through calcium concentration effect on parasitaemia.

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