A process for oxidizing environmentally harmful compounds which participate in atmospheric photochemical reactions to produce for example ozone and undesirable smog constituents from a fluid, in particular a gas, volatile organic compounds (VOC) including hydrocarbons, CO and any other constituent that participates in atmospheric photochemical reactions to produce for example ozone or smog constituents and combustible compounds to be removed from a gas stream for reasons of toxicity, photochemical reactivity or physical discomfort such as irritants, particulates, odor sources and so on, and compounds which may cause upper atmosphere ozone depletion or lower atmosphere ozone formation. The uncoated randomly oriented mesh-like structure preferably has a porosity greater than about 85%. The coated randomly oriented mesh-like structure preferably has a porosity greater than about 65%. Preferred embodiments of structured packing and monoliths are disclosed each having a catalyst for oxidizing the volatile organic compound(s). In the disclosed embodiments, corrugated mesh-like sheets are arranged in mirror image angular relative orientations relative to the input gas flow direction in a range of angles from about 30° to about 80°. In a further embodiment, the corrugated sheets are in series with a monolith structure with the corrugated sheets initially receiving the fluid with the environmentally harmful compounds to be oxidized and which fluid then flows into the monolith structure to complete the oxidation. In other embodiments, the mesh-like structure may have different configurations.