# Calibration and Validation of an Autonomous, Novel, Low-Cost, Dynamic Flux Chamber for Measuring Landfill Methane Emissions

## TL;DR

A low-cost methane flux chamber was developed and validated for measuring landfill emissions, offering a portable and affordable solution for continuous and spatially broad monitoring.

## Contribution

A novel, low-cost dynamic flux chamber with a calibration system for methane emissions was designed and validated for field use.

## Key findings

- The flux chamber successfully measured methane fluxes from 0 to 150 g/m²-day with good accuracy in laboratory and field tests.
- A piecewise calibration function using low-cost sensors achieved root mean squared errors of 3.1 ppm to 307 ppm across methane concentration ranges.
- The system demonstrated autonomous and continuous operation in a real-world landfill setting.

## Abstract

What are the main findings?

Low-cost air quality sensors can be leveraged in the development and optimization of an affordable and portable methane flux chamber.

A calibration system for low-cost sensors was developed to operate in a laboratory setting and achieve measurements capable of covering a wide dynamic range of methane emissions from landfills.

What is the implication of the main finding?

Low-cost flux chambers can be deployed in large numbers across a landfill to support simultaneous and continuous measurements achieving spatially and temporally broad information about emissions.

Low-cost sensors can be effectively calibrated across a very wide range of methane concentrations while mitigating the confounding influence of ambient temperature and humidity variations.

A low-cost, dynamic flux chamber optimized for landfill emissions measurement was designed, fabricated, calibrated, and validated for measurements of methane flux ranging from 0 to 150 g/m2-day. A centrifugal blower fan and a flow meter were plumbed in series to draw a bypass flow through the flux chamber. Both ambient and chamber methane concentrations were measured using the arrays of four low-cost metal oxide sensors. Leveraging the sensors’ overlapping sensitivity to changes in methane concentration, temperature, and humidity, multiple linear regressions were trained on laboratory data and combined into a piecewise methane calibration function. An algorithm was developed to select the most useful interaction terms among all sensor responses to optimize the predictors in each model. The piecewise regions for methane measurement were 0–100 ppm, 100–1500 ppm, and 1500–12,000 ppm. The root mean squared errors for each piecewise region were 3.1 ppm, 21 ppm, and 307 ppm, respectively. Controlled quantities of methane were delivered to the flux chamber in a laboratory setting for validation. Measurements yielded good agreement with an RMSE and MBE of 7.3 g m−2 d−1 and 2.2 g m−2 d−1, respectively. The flux chamber was tested at a closed landfill to validate its ability to autonomously and continuously operate in the field.