Some of the key types of sensors used in urban air quality monitoring include: Particulate Matter (PM) Sensors: These sensors measure concentrations of particulate matter Nitrogen Dioxide (NO2) Sensors: NO2 is a common urban pollutant, often produced by vehicle exhaust and industrial processes. Sulfur Dioxide (SO2) Sensors: Commonly produced by industrial processes, SO2 levels are often monitored using ultraviolet fluorescence or electrochemical sensors. Ozone (O3) Sensors: Ozone at ground level is a harmful pollutant, and its concentration is typically monitored using ultraviolet (UV) photometry or electrochemical cells. Carbon Monoxide (CO) Sensors: CO is a colorless, odorless gas resulting from incomplete combustion. It's usually monitored in urban environments using electrochemical sensors. Volatile Organic Compounds (VOCs) Sensors: VOCs are emitted from a variety of sources, including vehicle exhaust, industrial processes, and consumer products. Meteorological Sensors: These sensors measure environmental conditions like temperature, humidity, wind speed, and wind direction, which are important for understanding and interpreting air quality data.^[1]

Monitoring emissions from factories in real-time involves a variety of sensors and instruments designed to measure different types of pollutants. These sensors are often networked together and connected to a central monitoring system that collects, analyzes, and reports data in real time. This enables factory operators and regulatory agencies to track emissions continuously and ensure compliance with environmental regulations, as well as to make informed decisions about emission control and reduction strategies. Gas Analyzers: These sensors are used to detect and quantify specific gases in the air, such as carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen oxides (NOx), and volatile organic compounds (VOCs). Particulate Matter (PM) Sensors: These sensors measure the concentration of particulate matter in the air. Opacity Monitors: These are used to measure the opacity of emissions from smokestacks, which is an indicator of particulate matter concentrations. Flame Ionization Detectors (FID): FIDs are used to measure total hydrocarbon levels in emissions. FTIR (Fourier Transform Infrared Spectroscopy) Analyzers: These analyzers can detect a wide range of gases and are particularly useful for identifying complex mixtures of pollutants. UV Spectrometers: Ultraviolet spectrometry can be used to measure specific gases like ozone (O3) and sulfur dioxide (SO2) based on their absorption characteristics in the UV range. Chemical Sensors and Biosensors: These are used to detect and measure specific chemical compounds in emissions. Temperature, Pressure, and Flow Sensors: These sensors provide additional data on the emission conditions, such as the temperature and pressure of the emitted gases and the flow rate of emissions."^[2]