Drones Enhance Air Quality Monitoring in Delhi, Revealing Hidden Pollution Levels
New Delhi, India – A recent study conducted in the Delhi metropolitan region has demonstrated the effectiveness of using drones equipped with low-cost sensors to investigate air pollution in the lower atmosphere. The research, coordinated by Assistant Professor Ajit Ahlawat from the Leibniz Institute for Tropospheric Research (TROPOS) and TU Delft, reveals that particulate matter (PM) concentrations can vary significantly with altitude, challenging current air quality models.
The Challenge of Vertical Air Pollution Data
The metropolitan area of New Delhi, home to over 30 million people, faces some of the highest air pollution levels globally, particularly during winter smog. Traditionally, air quality monitoring has relied on ground-based measurements and satellite observations. However, data from the lowest layers of the atmosphere – crucial for understanding pollutant concentrations – has been limited. Understanding the vertical distribution of pollutants is vital, as it directly impacts the overall concentration of pollutants in the air.
Drone Technology and Low-Cost Sensors
Researchers addressed this gap by deploying drones fitted with affordable PM sensors, including the AE-51 micro-aethalometer, alongside meteorological sensors. A key innovation was the design of a custom-made vertical aerosol sampling inlet, positioned approximately 30 centimeters above the drone’s rotor blades. This design minimized air turbulence caused by the rotors, ensuring more accurate measurements. A silica gel dehumidifier was too incorporated to address challenges posed by high humidity, which can interfere with air sampling, and analysis.
Key Findings: Altitude and Pollution Concentration
The study found that PM2.5 concentrations can be substantially higher at altitude. For example, on March 18th, 2021, PM2.5 concentrations at 100 meters were up to 60 percent higher than at ground level, reaching approximately 160 µg/m3 compared to 100 µg/m3 on the ground. This suggests that current air quality models underestimate PM2.5 concentrations, especially during morning smog events, as published in Nature npj Clean Air.
Understanding Smog Formation in Delhi
The research also shed light on the chemical composition of pollutants at different times of day. Organic substances were dominant during the day, although inorganic substances like nitrate and chloride increased at night, likely due to biomass and waste burning, as well as industrial emissions. Nitrate and ammonium concentrations peaked in the early morning, coinciding with humid and cold conditions. NOx levels peaked around 9 pm, attributed to vehicle and industrial emissions trapped under a stable boundary layer. PM2.5 levels steadily increased from 6 pm to 8 am, highlighting the role of both primary emissions and secondary aerosol formation in smog development.
Implications for Air Quality Management
The findings underscore the importance of targeting emission control measures at nocturnal sources and addressing humidity-driven secondary aerosol processes. The study also indicates that current air quality models, such as the WRF-Chem model, may have a “dry bias” that limits their ability to accurately simulate aerosol hygroscopic growth in high humidity conditions. Researchers believe that integrating cost-effective PM sensors into existing air monitoring systems is a crucial step towards improving air quality management and closing observation gaps in the lower boundary layer.
International Collaboration
This research involved an international team of scientists from India, the Netherlands, Germany, China, Greece, Great Britain, Thailand, Czechia, and Cyprus.
Sources: Envirotec Magazine, EurekAlert!, MyScience