About This Project

Affordable methane sensors capable of measuring concentrations around atmospheric level are a crucial tool needed to develop soil-based methane removal strategies. This project aims to develop a suite of printable, low cost sensors that accurately measure methane in the presence of potentially interfering gasses.

Ask the Scientists

Motivating Factor

Methane is responsible for about 30% of global warming to date. Future tipping point scenarios could result in large additional methane releases, for example from thawing permafrost.

Natural ecosystems can remove methane by oxidizing it. Soils naturally account for 11-49 Tg CH4/yr, or about 5% of global methane removals [1]. The size of this sink doubled in the 20th century and is projected to double again by the end of the 21st century [2], but current and future soil methane uptake rates have significant uncertainty.

Specific soil management practices may increase the amount of methane that soils oxidize, for example adding compost or crushed rock amendments, modifying rice paddy flooding schedules, or introducing methanotrophs to ecosystems, [3,4,5]. However, much remains unknown about these interventions: how much methane could they sink? Which practices are most effective? How do soil type and environmental conditions impact methane uptake rate for each management practice?

Specific Bottleneck

Ecologists and soil biogeochemists can modify soils at study sites and monitor methane dynamics to answer the questions above. These experiments need to gather data at high spatial and temporal resolution because emissions are highly variable [6] and must be replicated in various soil and environmental conditions. For this, affordable, easy-to-use sensors capable of measuring methane at near-atmospheric concentrations (~2 ppm) are needed.

Methane monitoring systems with sensitivity below 1 ppm are expensive ($90k-$220k) and can measure at most 16 locations in a field. Low-cost metal oxide sensors (~$30-50) have numerous limitations [7,8]:

• Sensors are calibrated between 300-10,000 ppm

• Poor accuracy below ~50 ppm

• Poor selectivity–they respond to temperature, humidity, and concentrations of other gasses

• Complicated calibration is needed to account for interference from other gasses

• High sensor-to-sensor variation requires individual calibration for each sensor

Actionable Goals

Ideally, inexpensive methane sensors with lower detection limit ~500 ppb which are insensitive to moisture, oxygen, temperature, or other factors should be developed, but there are other technical solutions that can bring high temporal and spatial resolution methane sensing closer to reality.

• Characterize different sensing materials’ response to methane and physical and chemical conditions that are found in methanotrophic and methanogenic soils.

• Design a system to monitor interfering conditions and calibrate their impacts out of methane measurements

This work should be informed by the soil methane flux research community to ensure that the sensors account for gasses at concentrations likely to be encountered in soils.