Particulate matter (PM) is a complex mixture of solid particles and liquid droplets suspended in the air with varying size, shape, and chemical composition which intensifies significant concern due to severe health effects. Based on the well-established human health effects of outdoor PM, health-based standards for outdoor air have been promoted (e.g., the National Ambient Air Quality Standards formulated by the U.S.). Due to the exchange of indoor and outdoor air, the chemical composition of indoor particulate matter is related to the sources and components of outdoor PM. However, PM in the indoor environment has the potential to exceed outdoor PM levels. Indoor PM includes particles of outdoor origin that drift indoors and particles that originate from indoor activities, which include cooking, fireplaces, smoking, fuel combustion for heating, human activities, and burning incense. Indoor PM can be enriched with inorganic and organic contaminants, including toxic heavy metals and carcinogenic volatile organic compounds. As a potential health hazard, indoor exposure to PM has received increased attention in recent years because people spend most of their time indoors. In addition, as the quantity, quality, and scope of the research have expanded, it is necessary to conduct a systematic review of indoor PM. This review discusses the sources, pathways, characteristics, health effects, and exposure mitigation of indoor PM. Practical solutions and steps to reduce exposure to indoor PM are also discussed.

Alkaline residue, a common solid waste from the Lianyungang Soda Plant, China, was, respectively, modified by FeCl₃·6H₂O (FeCAR) and MnSO₄·H₂O (MnCAR) for arsenate adsorption. The specific surface areas and morphologies of FeCAR and MnCAR were determined by BET and SEM methods. The adsorption properties including adsorption kinetics, isotherms, and thermodynamics were investigated in depth. The experimental data were analyzed by different kinetic and isotherm models, and the results showed that for both FeCAR and MnCAR, the pseudo-second-order kinetic model was the best-fit model for describing the adsorption process while the Langmuir isotherm model provided the best fit to the equilibrium data. The maximum adsorption capacity calculated from the Langmuir equation was 44.4 mg/g for FeCAR and 22.6 mg/g for MnCAR, which were greater than other low-cost materials. The positive value of ΔH° indicated that the arsenate adsorption on adsorbents was endothermic, which was supported by the increasing adsorbed amount of arsenate with temperature. The positive value of ΔS° reflected good affinity of arsenate toward the modified alkaline residue. Overall, alkaline residue modified by iron or manganese was a very promising alternative adsorbent for removing arsenate from groundwater.