# Are Ammonia Sensors Ready for Outdoor Use?

## TL;DR

This study evaluates ammonia sensors for outdoor use and finds they are not yet reliable enough for routine monitoring.

## Contribution

The paper provides a field evaluation of six ammonia sensors against a reference instrument in an agricultural setting.

## Key findings

- Only three sensors (TB600B, AM1 LC, AM2 HC) showed positive correlation with the reference analyzer.
- All tested sensors face significant challenges in accuracy, precision, and data capture.
- Outdoor ammonia sensors are not yet suitable for routine deployment.

## Abstract

Ammonia (NH3) gas is primarily an agriculture
atmospheric
pollutant, and measuring near-emission sources is essential for understanding
NH3 emission plumes. Sensors in theory are attractive alternative
monitoring methods due to their high-time data resolution, size, and
lower costs; however, there are metrological and technical challenges.
NH3 sensors operating in the subppm range (typical of near-emission
source concentrations) are relatively new to the market, and while
promising, there are metrological and technical challenges, especially
in outdoor environments. Six NH3 sensors were evaluated
under field conditions at a poultry house emission simulation site,
Whim Bog, Scotland (3.4 g of NH3 min–1). Five electrochemical (TB600B, PS1, ECtox, duplicated
AM1 low concentration (LC), and AM2 high concentration (HC)) and one
chemiresistive-polymer (MELBA) sensors were tested and compared to
a cavity ring-down instrument (Picarro G2103 NH3 analyzer)
as a reference method. Only the TB600B (R
2 = 0.59–0.84), AM1 LC (R
2 = 0.7–0.9),
and AM2 HC (R
2 = 0.71–0.9) demonstrated
a positive correlation to the reference analyzer, being potentially
capable of delivering indicative NH3 concentrations, with
the caveat that the AM sensors had very low data capture and their
performance may improve once the sensors operate for longer. All sensors
tested have major technical challenges including accuracy, precision,
response time, manufacturer deployment guidelines, sensor lifecycle
metrics, software engineering, and data traceability. This study highlights
the need for improvement in the NH3 sensor industry and
among suppliers, and concludes that outdoor ammonia sensor measurements
are not yet ready for routine use.