Air Pollution Monitoring with Nanoscaled Materials in Chemoresistive Gas Sensors

Air pollution is a pressing global concern due to its negative effects on human health and our ecosystem. For instance, pollutants, including particulate matter, volatile organic compounds, nitrogen- and sulfur-based gases, and ozone, are known to increase the incidence rates of respiratory, cardiovascular, and various cancer types, among others. Comprehensive monitoring of key gaseous pollutants is, therefore, critical to enforce adherence to regulatory limits or to control personal exposure. In this review, we analyze the progress on nanostructured and porous chemoresistive gas sensors over the last five years and critically compare their performance to air pollution guidelines. We start with a discussion of the major outdoor and indoor pollutants, describing their main sources and the associated health effects arising from short- and long-term exposures to concentrations exceeding national and regional limits. Thereafter, we describe the working mechanism of chemoresistive gas sensors along with their key performance parameters, followed by a literature survey of several nanoscaled porous materials for such applications. We highlight different engineering strategies focused on structural, morphological, and electronic control through heterostructures, surface functionalization, and metal-organic framework templates that tune air pollutant adsorption, catalytic conversion on their surfaces, and sensor signal generation. Finally, we briefly discuss the integration of these gas-sensing technologies into functional devices to translate material and surface innovation into environmental monitoring platforms for consumer electronics, wearables, and smart-home solutions.