Artificial olfaction, also known as an electronic nose, is a gas identification device that replicates the human olfactory organ. This system integrates sensor arrays to detect gases, data acquisition for signal processing, and data analysis for precise identification, enabling it to assess gases both qualitatively and quantitatively in complex settings. This article provides a brief overview of the research progress in electronic nose technology, which is divided into three main elements, focusing on gas-sensitive materials, electronic nose applications, and data analysis methods. Furthermore, the review explores both traditional MOS materials and the newer porous materials like MOFs for gas sensors, summarizing the applications of electronic noses across diverse fields including disease diagnosis, environmental monitoring, food safety, and agricultural production. Additionally, it covers electronic nose pattern recognition and signal drift suppression algorithms. Ultimately, the summary identifies challenges faced by current systems and offers innovative solutions for future advancements. Overall, this endeavor forges a solid foundation and establishes a conceptual framework for ongoing research in the field.

Increasing carbon dioxide (CO₂) concentrations threaten human production and life. Currently the equipment used for CO₂ monitoring is heavy and expensive, without a portable CO₂ detector that is inexpensive and resistant to interference. Here we designed a portable CO₂ detector based on no-dispersive infrared sensors to measure CO₂ concentration. The detector, which has a mass of 1 kg, is powered by a lithium battery with dimensions of 200 mm (length) × 150 mm (width) × 100 mm (height). Considering the fact that field observations are susceptible to humidity, a series of experiments were carried out to reduce the humidity interference on sensor responses at a laboratory. The values of humidity and CO₂ variation were used in a regression model analysis to determine a quadratic function with an R² above 0.94. The detector was compared with a reference analyzer in ambient CO₂ measurement during a 7-day field campaign in Hangzhou, China. After humidity correction, the data show better correlation with the reference data, with the R² 0.62–0.97 increasing from 0.62–0.97 compared to before the correction and the value deviation decreasing to less than 3%. Cluster analysis of sensors revealed a reduction in average relative deviation of up to 1.4% as the number of sensors increased.

Ozone (O₃) has attracted considerable attention due to its harmful effects on the ecosystem and human health. The Yangtze River Delta (YRD), China in particular has experienced severe O₃ pollution in recent years. Here, we conducted a long-term observation of O₃ in YRD to reveal its characteristics. The O₃ concentration in autumn was the highest at 72.76 ppb due to photochemical contribution and local convection patterns, with its lowest value of 2.40 ppb in winter. O₃ exhibited strong diurnal variations, showing the highest values in the early afternoon (15:00–16:00) and the minimum in 07:00–08:00, specifically, peroxyacetyl nitrate (PAN) showed similar variations to O₃ but PAN peak usually occurred 1 h earlier than that of O₃ due to PAN photolysis. A generalized additive model indicated that the key factors to O₃ formation were NO₂, PAN, and temperature. It was found that a certain temperature rise promoted O₃ formation, whereas temperatures above 27 °C inhibited O₃ formation. An observation-based model showed O₃ formation was VOCs-limited in spring and winter, was NO_x-limited in summer, and even controlled by both VOCs and NO_x in autumn. Thus, prevention and control strategies for O₃ in the YRD are strongly recommended to be variable for each season based on various formation mechanisms.

Currently, traffic-related sources are considered to be one of the major contributors to air pollutants in urban areas. As the number of motor vehicles increases, the impact of traffic-related air pollutants (TRAPs) on human health has also increased in recent years. People are easily exposed to TRAPs in their daily lives. However, long-term exposure to TRAPs can have adverse health effects. Mobile monitoring is more flexible compared to traditional urban monitoring stations and can effectively obtain the spatial variation characteristics of air pollutants. We mounted a sensor package on an electric bicycle and conducted mobile measurements of CO, NO₂ and SO₂ on a circular road in the center of Shaoxing, a city in the center of the Yangtze Delta, China. The CO, NO₂ and SO₂ concentrations were observed to be higher in the morning and evening rush hours, and the three pollutants show different seasonal and spatial variation characteristics. CO concentration was higher in urban arterial and crossroads. NO₂ concentration was variable, alternating between high and low concentrations. SO₂ concentration was relatively stable and aggregated. This study provides important information on the spatial and temporal variations of TRAPs, which helps commuters understand how to effectively reduce pollutant exposure during personal travel.

Fine chemical industrial park (FCIP) is a major source of atmospheric pollutants in China. A long-term high spatial resolution monitoring campaign on air pollutants had been firstly conducted in a major FCIP in Yangtze River Delta (YRD) from December 2019 to November 2020. The grid-based monitoring platform consisting of 30 miniature air quality monitoring stations (AQMSs) provided comprehensive coverage of a FCIP, and long-term monitoring studies solved the problem of lack of clarity about pollution sources in industrial parks. Overall, NO₂ pollution was particularly high in the pharmaceutical industry, while TVOCs and O₃ pollution were most serious in the textile dyeing industry, with PM pollution much higher in the metal smelting industry than in other industries, and in the leather industry, O₃ pollution was relatively severe. The spatial and temporal variations of air pollutants showed that higher PM, CO and NO₂ concentrations were revealed in winter while lower in summer due to better meteorological diffusion conditions. TVOCs concentrations were higher with an average of 1954 ppb in summer possibly due to their increased volatilization from their sources at higher ambient temperatures. O₃ concentrations were at their peaks in spring (88.8 μg m⁻³) and early fall (78.5 μg m⁻³). The daily trends of O₃ precursors (TVOCs and NO₂) were clearly negatively correlated with O₃, and they showed bimodal peaks due to anthropogenic activities, plant emissions, lowering of the mixed boundary layer, etc. The O₃ formed in FCIP was judged to be NO₂-limited during the monitoring period based on the ratios of NO₂ to TVOCs. Therefore, the effective strategy to reduce O₃ formation in FCIP is to decrease the ambient NO₂ concentration. Based on Pearson correlation coefficients, it appeared that WS promoted O₃ formation through long-term transport and that high air temperatures also contributed to O₃ formation in the environment. It was also stated in the study that the closer the residential area is to the industrial sources, the more significant the correlation. Thus, the results of this study will also be helpful for policymakers to design pollutant control strategies for different industries to mitigate the impact of pollutants on human health.