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Accurate and Precise Atmospheric Ammonia Measurement: From Emission Sources, Analytical Methods to Mitigation Strategies

Written By

Hongming Yi

Submitted: 06 October 2025 Reviewed: 30 October 2025 Published: 07 January 2026

DOI: 10.5772/intechopen.1013785

Air Pollution IntechOpen
Air Pollution Emerging Contaminants and Control Strategies Edited by Hugo Albeiro Saldarriaga Noreña and Jose Gustavo Ronderos-Lara

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Air Pollution - Emerging Contaminants and Control Strategies

Hugo Albeiro Saldarriaga Noreña and Jose Gustavo Ronderos-Lara

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Abstract

Ammonia (NH₃) is a key reactive nitrogen species with critical roles in local, regional, and global nitrogen cycling, and it is increasingly recognized for its impact on environmental pollution and climate change. As a major precursor of secondary particulate matter, NH₃ contributes to fine aerosol formation, which adversely affects air quality and human health, particularly through respiratory and cardiovascular diseases. Accurate and precise measurement of atmospheric NH₃ is therefore essential to quantify its concentrations, elucidate sources and sinks, and understand deposition processes. This review systematically introduces and evaluates the current methodologies and instrumentation for NH₃ measurement, including chemical, electrochemical, optical, and remote-sensing approaches. The advantages, limitations, and comparative performance of these techniques are analyzed to provide guidance for selecting appropriate measurement strategies. Special emphasis is placed on open-path laser-based instruments, which enable high-sensitivity, high-temporal-resolution measurements in field campaigns, facilitating improved characterization of spatial and temporal NH₃ distributions, particularly in undermonitored regions. Finally, the review synthesizes current mitigation and control strategies for NH₃ emissions, highlighting approaches applicable to agricultural and industrial sectors. Policy implications and practical recommendations are discussed to support evidence-based decision-making for emission reduction. By integrating advances in measurement techniques with emission control strategies, this work aims to provide a comprehensive framework for understanding and managing atmospheric NH₃, ultimately contributing to improved air quality, ecosystem protection, and human health.

Keywords

  • ammonia measurement
  • accuracy and precision
  • methodology
  • open-path instruments
  • emission and mitigation

1. Introduction

The atmospheric nitrogen cycle moves nitrogen among the air, land, and oceans through processes such as fixation, nitrification, assimilation, and denitrification. It is vital for all life because it helps produce proteins, DNA, and other essential molecules. This cycle supports plant growth, maintains soil fertility, and sustains healthy ecosystems across the biosphere. Ammonia (NH₃) is a key component of the atmospheric nitrogen cycle, playing a critical role in atmospheric chemistry and aerosol formation [1]. As a major precursor of secondary particulate matter, NH₃ strongly influences air quality [2, 3], climate, and human health. The pathways of atmospheric processing are illustrated in Figure 1a to facilitate understanding [4]. As the most abundant alkaline gas in the atmosphere, NH₃ readily neutralizes acidic components, modifying cloud pH and regulating overall atmospheric acidity. Beyond its neutralizing capacity, NH₃ contributes to new particle formation, increasing the number of airborne particles. For example, NH₃ reacts with acidic gases such as sulfuric acid (H₂SO₄) and nitric acid (HNO₃) to form ammonium salts (e.g., ammonium sulfate, ammonium nitrate), which are major constituents of fine particulate matter (PM₂.₅) [5–8], as depicted in Figure 1b [8]. Furthermore, key chemical reactions underlying these processes are summarized in Table 1 [5]. NH₃-driven PM₂.₅ formation degrades air quality, reduces visibility, and disrupts ecosystems [9]. Additionally, ammonia-mediated particulate matter can alter Earth’s radiative balance, influencing climate systems. Elevated PM₂.₅ concentrations are strongly associated with adverse health outcomes, particularly.

Figure 1.

(a) Conceptual diagram of the nitrogen cycle highlighting the transformations, fate, and impacts of ammonia (NH₃) and ammonium (NH₄⁺). The schematic aligns with key sections of this manuscript, including human health and visibility, climate forcing, ecosystem impacts, atmospheric emissions, transport and fate, and ammonia management [4]. (b) Major transformations within the nitrogen cycle and the associated chemical reactions [8].

# Reaction Rate constant Rate estimate at 298 K (with uncertainty factors)
R1 NH3 + OH→NH2 + H2O k1 = 1.7 * 10−12 * e −710/T 1.6 (1.2) * 10−13 cm3 molecule−1s−1
R2 NH2 + O3→NH2O + O2 k2 = 4.3 * 10−12 * e−930/T 1.9 (3.0) * 10−13 cm3 molecule−1s−1
R3a NH2 + NO2→NH2O + NO k3a = 2.0 * 10−11 * (T/298)−1.3 * (0.75) 1.5 (1.6) * 10−11 cm3 molecule−1s−1
R3b NH2 + NO2→N=N=O + H2O k3b = 2.0 * 10−11 * (T/298)−1.3 * (0.25) 0.5 (1.6) * 10−11 cm3 molecule−1s−1
R4 NH2 + NO→N≡N + H2O k4 = 4.0 * 10−12 * e450/T 1.8 (1.3) * 10−11 cm3 molecule−1s−1
R5a NH2 + HO2→NH3 + O2 k5a = 3.4 * 10−11 * (0.85) 2.9 (2.0) * 10−11 cm3 molecule−1s−1
R5b NH2 + HO2→HNO + H2O k5b = 3.4 * 10−11 * (0.01) 3.4 (2.0) * 10−11 cm3 molecule−1s−1
R5c NH2 + HO2→NH2O + OH k5c = 3.4 * 10−11 * (0.14) 4.8 (2.0) * 10−12 cm3 molecule−1s−1
R6 NH2O + O3→NH2 + 2O2 k6 = 2.0 * 10−14 2.0 (± 1.5) * 10−14 cm3 molecule−1s−1
R7 NH2O + OH → HNO + H2O k7 = 1.8 * 10−10 1.8 (10) * 10−10 cm3 molecule−1s−1
R8 HNO + O2 → NO + HO2 k8 = 3.65 * 10−14 * e−4600/T 7.2 (2) * 10−21 cm3 molecule−1s−1

Table 1.

Rate constants (cm3 molecule−1 s−1) for representative chemical reactions involved in the ammonia oxidation process during atmospheric nitrogen cycling [5].

Note [5]: Reaction R8 is assumed to occur rapidly and is thus not explicitly simulated. Rate estimates are provided for each reaction at 298 K, with the uncertainty factor represented in red within parentheses in all cases, except for reaction R6, where it represents an absolute error estimated by the study for the measurement at 296 K.


Respiratory and cardiovascular diseases [10–12]: In the United States and Europe [13–15], NH₃ contributes approximately 30% and 50% of PM₂.₅, respectively. Ammonia runoff into water bodies promotes eutrophication, affecting aquatic life and drinking water quality, while deposition onto soils can increase acidity, reducing biodiversity and nutrient availability for plants. Consequently, it is essential to accurately and precisely measure NH3 in the atmosphere to thoroughly understand NH₃ sources, deposition processes, and atmospheric behavior.

The ongoing rise in atmospheric NH₃ emissions poses substantial risks to environmental quality, public health, and climate. Over the past two decades, research at global, regional, and local scales has increasingly focused on these issues. Agricultural activities remain the dominant NH₃ source, primarily through fertilizer application and livestock emissions [3, 5, 14]. Additional contributions arise from industrial processes, vehicular exhaust, and natural sources such as soils and oceans. Globally, agriculture accounts for approximately 80–95% of total NH₃ emissions, though fossil fuel combustion and vehicle emissions can be significant in certain regions [15].

The deposition of atmospheric ammonia (NH₃) has far-reaching ecological consequences [5, 14]. Excess nitrogen deposition can drive eutrophication and acidification in sensitive ecosystems – including forests, wetlands, and aquatic environments – resulting in biodiversity loss and ecosystem imbalance [15–17]. When NH₃ is deposited onto soils, it can cause direct foliar damage to vegetation and indirectly disrupt the nitrogen cycle by acidifying soils, thereby reducing soil quality, fertility, and long-term productivity. These effects underscore the dual role of NH₃ as both a pollutant and a driver of broader biogeochemical changes [18].

Despite its environmental significance, accurately measuring atmospheric NH₃ remains a major scientific challenge [16, 17]. As a highly reactive and “sticky” gas, NH₃ readily adsorbs to and desorbs from instrument surfaces, complicating its quantification due to the artificial loss mechanism. Meanwhile, its typically low and highly variable atmospheric concentrations – often in the parts-per-billion by volume (ppbv) range – further hinder detection. These challenges affect the accuracy, precision, comparability, and reliability of both ground-based and satellite observations [19–21]. Addressing these issues requires careful calibration, the development of robust measurement techniques, and the integration of complementary approaches, including in-situ monitoring, satellite remote sensing [22], and atmospheric modeling.

Advancing scientific understanding of NH₃ emissions and their impacts is critical for informing effective policy decisions. Identifying major emission sources, elucidating ammonia’s role in secondary particulate matter formation, and developing mitigation strategies are essential to reducing the environmental, climatic, and public health burdens associated with reactive nitrogen. This review, therefore, synthesizes current knowledge and outlines future research priorities through an integrated assessment of in-situ measurements, remote sensing datasets, modeling studies, and policy frameworks.

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2. Ammonia emission sources and estimation

2.1 Ammonia (NH3) emission sources

Ammonia emissions come from both human-related (anthropogenic) activities and natural processes-related sources. Agriculture is the dominant anthropogenic source of atmospheric NH₃, primarily from livestock waste and synthetic fertilizer application, along with industrial processes such as fertilizer production and waste treatment. Other anthropogenic sources include biomass burning, mobile sources (e.g., vehicles), and power generation, as well as other unidentified or minor contributors. Natural sources, including soil and oceanic decomposition, also contribute to NH₃ emissions. Table 2 summarizes these major emission sources. For illustration, Figure 2 [4] presents the relative contributions of anthropogenic sources in the United States, providing insight into the characteristics and distribution of NH₃ emissions.

Ammonia sources Detailed breakdown Notes
Agriculture Livestock waste Urea in manure and urine converted to ammonia by enzymes in feces and soil. Ammonia volatilizes from manure, slurries, and storage.
Fertilizer use NH3 from the application of urea-based fertilizers and other nitrogen-rich fertilizers to fields, lawns, and crops.
Industrial processes and fertilizer production NH3 generated in the manufacturing of synthetic fertilizers, particularly in the fertilizer industry and through the Haber–Bosch process.
Food and pharmaceutical production NH3 from the processes involving the breakdown of organic matter or nitrogenous wastes.
Waste treatment NH3 emissions from the treatment of industrial and domestic sewage.
Natural and some anthropogenic sources Decomposition Natural degradation of proteins and urea by microorganisms in soil and other organic matter.
Oceans A significant natural source of ammonia.
Biomass burning Wildfires Release of ammonia during burning.
Burning plant matter
Mobile sources Vehicles A minor but present anthropogenic source.
Fossil fuel combustion Burning: power plants and other applications A smaller contribution.
Others Unknown and unidentified Contribution amount < 1%.

Table 2.

The main NH3 emission sources summarized from recent publications [3, 4, 12, 14, 15].

Figure 2.

The percentage contribution of NH3 emission from anthropogenic sources in the United States in 2020, based on the analysis of U.S. EPA's 4.97 million tonnes of anthropogenic sources [4].

Agriculture, as the largest global source of ammonia (NH₃), contributes approximately 80–95% of emissions in developed countries [3, 4]. The global average NH3 emission from agriculture is about 81%, based on bottom-up and top-down estimation methods [3, 4, 18]. Global NH₃ emissions have nearly tripled between 1960 and 2022, with the vast majority of this increase originating from agricultural activities [18]. The 1960s marked the onset of the Green Revolution, particularly in Asia and Latin America, characterized by the widespread adoption of high-yield crop varieties and fertilizer-intensive production practices, often supported by government and international subsidies [15, 18]. During this period, the Haber–Bosch process for synthetic nitrogen fertilizer production matured and expanded globally. As a result, nitrogen fertilizer application to soils increased from 19 million metric tonnes in 1961 to 109 million metric tonnes in 2022, driving the substantial rise in agricultural NH₃ emissions [9, 15, 18].

Ammonia (NH₃) emissions are continuing to increase in many low- and middle-income countries (LMICs) [15, 18], including Nigeria, Indonesia, Pakistan, and India [18]. Several factors contribute to this trend. Rapid agricultural expansion driven by population growth has intensified cropping systems, particularly for nitrogen-demanding crops such as rice and wheat. Concurrently, livestock populations are growing to meet rising demand for meat, dairy, and eggs, leading to increased manure production [15, 16, 18, 23, 24]. In many LMICs, manure management remains rudimentary, resulting in substantial NH₃ emissions. Regulatory frameworks for controlling ammonia emissions are generally weak or absent, and environmental enforcement is limited. Similar challenges are observed in wastewater treatment systems, further exacerbating NH₃ emissions.

2.2 Underestimations of the ammonia emission rate

Although the main sources of atmospheric ammonia (NH₃) have been identified and their contributions quantified, NH₃ emission rates are frequently underestimated due to limitations in emission inventories, measurement techniques, and modeling approaches [16–22].

Firstly, the underestimation of NH₃ emissions can largely be attributed to incomplete emission inventories and missing sources. Satellite observations indicate that global NH₃ emissions are substantially higher than those reported in bottom-up inventories. Some studies [16, 22] used remote sensing to quantify county-level annual NH₃ emissions and found that known anthropogenic sources are approximately 80% higher than inventory data suggest. When additional anthropogenic and natural sources are included, total emissions are up to four times greater than previously estimated. Newly recognized emissions, though small, are detectable over extensive regions, such as the Russian taiga, which had been assumed to have negligible NH₃ emissions. Observed emissions align more closely with reported values in countries with regulatory frameworks, such as those in the European Union. Despite differences in magnitude, satellite-based analyses reproduce familiar global hot spots, including central United States, northwestern Europe, the Po Valley, the Nile Delta, the Indo-Gangetic Plain, and eastern China [13, 17, 18, 20]. Firstly, emission inventories often fail to account for all sources. Mobile emissions from on-road and off-road vehicles are frequently underestimated by factors of 2–5 in older inventories [21]. While many mitigation strategies focus on reducing nitrogen oxide (NOx), some control systems, such as selective catalytic reduction, can lead to unintended increases in NH₃ emissions [17–21]. Industrial emission estimates often neglect indirect sources, including flue gas treatment by-products; in China, a 2025 study reported that industrial NH₃ emissions were 3–10 times higher than previous bottom-up estimates [22]. Agricultural NH₃ emissions are also highly uncertain, as limited data on practices such as fertilizer application timing and method can lead to skewed estimates, particularly at high spatial and temporal resolution. In addition, in many regions, contributions from sources such as vehicles and industrial processes have been overlooked or inaccurately quantified, resulting in underestimates [16, 17]. Improving these estimates is critical for understanding NH₃’s role in particulate matter formation and its broader ecological impacts.

Secondly, measurement challenges persist. The physical and chemical properties of NH₃ complicate accurate field measurement. Its high polarity causes molecules to adhere to sampling surfaces, leading to “stickiness” that underestimates true concentrations [25, 26]. Sampling design is critical [27, 28]; incomplete mixing in emissions from livestock facilities can produce estimates ranging from 50% to 200% of actual values. Instrument interference further complicates measurements [29]: Infrared-based sensors are sensitive to water vapor, while chemiluminescence methods can be affected by NOx. Meteorological factors, such as low wind or temperature variations, can introduce significant errors in field methods such as energy balance measurements. Monitoring networks are limited; for instance, the U.S. Ambient Ammonia Monitoring Network (AMoN) [22] is sparse, heavily biased toward rural areas, and lacks the temporal resolution needed to capture urban emissions.

Thirdly, modeling and data limitations contribute to underestimation [16, 18, 22]. Atmospheric models contain inherent uncertainties due to simplified chemical mechanisms, deposition schemes, and coarse spatial resolution. Using uniform emission factors fails to capture local and seasonal variability – for example, NH₃ emissions from fertilizer applications differ according to crop schedules. Satellite observations, while valuable for spatial coverage, have limitations, including coarse resolution and uncertainties under low-temperature conditions, and their validation is constrained by sparse ground-based measurements. Inaccurate meteorological inputs, such as overestimated wind speeds, further bias model simulations, contributing to underestimates of NH₃ concentrations.

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3. Ammonia measurement methods

Based on the analysis of the systematic underestimation of NH₃ emission rates, it is essential to develop improved methodologies for accurate and precise ammonia measurement. These methods should encompass a range of observational approaches, including satellite-based remote sensing, atmospheric modeling [16, 22], and advanced in-situ monitoring techniques. Given that atmospheric NH₃ typically exists at very low concentrations – often from sub-ppbv to a few ppbv levels [27, 28, 30] – high-sensitivity in-situ measurement techniques are critically required to ensure reliable detection and quantification.

3.1 Satellites, remote sensing, and atmospheric model

Satellite-based infrared remote sensing provides a powerful approach for monitoring atmospheric ammonia (NH₃) by detecting its characteristic absorption features [31]. These observations enable global and regional assessments of NH₃ distribution, identification of emission hot spots, and analysis of long-term atmospheric trends. Satellite data are further integrated into atmospheric models to enhance simulations of NH₃ transport, chemical transformation, and interactions with aerosols and clouds, thereby improving the understanding of emission–concentration relationships.

Satellite remote sensing of NH₃ primarily relies on thermal infrared absorption spectroscopy. Because NH₃ absorbs radiation at specific infrared wavelengths, its presence and concentration can be retrieved from satellite measurements. Key instruments include the infrared atmospheric sounding interferometer (IASI) and the hyperspectral infrared atmospheric sounder (HIRAS). IASI has provided more than a decade of global NH₃ records, revealing significant spatial and temporal trends, while HIRAS produces global NH₃ distribution maps consistent with IASI observations [22, 31]. Both instruments retrieve total column NH₃ concentrations, representing the integrated abundance of ammonia from the surface to the top of the atmosphere. Satellite-based remote sensing thus offers consistent, large-scale monitoring, enabling global mapping of NH₃ emissions, long-term trend analyses, and hot spot identification – particularly in regions such as East Asia, India, and West Africa.

Atmospheric models [16, 31] play a complementary role by assimilating satellite-derived NH₃ data along with ground-based and meteorological observations to simulate transport processes, chemical transformations, and emission dynamics. These models provide an integrated framework to interpret satellite observations and assess the impacts of NH₃ on atmospheric chemistry and climate. Model validation is crucial for ensuring simulation accuracy, requiring high-quality observational datasets from both satellite and in-situ measurements [32].

Consequently, the continued development of precise and reliable in-situ NH₃ instrumentation remains essential for quantifying hot spots identified by satellite remote sensing and for advancing model performance and improving our understanding of the global nitrogen cycle.

3.2 In-situ measurement methods

In-situ monitoring of atmospheric NH₃ involves deploying sensors directly in the environment to obtain real-time, high-resolution concentration data. These techniques are essential for characterizing the complex spatiotemporal variability of NH₃ and for providing reliable datasets to support and validate atmospheric models discussed in Section 3.1. A variety of detection methods are available depending on sample type, required sensitivity, and specific application. Broadly, these methods can be categorized into chemical, electrochemical, semiconductor, and optical techniques [29, 33–35], as summarized in Table 3.

Method Sample type Advantages Disadvantages Typical application
Chemical and colorimetric Gas and liquid Low-cost, simple, visual indication, portable options. Qualitative or semi-quantitative, affected by interferences. Leak detection, water quality testing, laboratory screenings.
Electrochemical Gas, liquid High selectivity, accurate for low-range measurement, low power consumption, portable. Limited lifetime, can be degraded by high concentrations, and sensitive to temperature/humidity. Industrial and personal safety monitoring.
Semiconductor Gas Simple, low-cost, high sensitivity at high temperatures, durable. Low selectivity, requires a high operating temperature, and is affected by humidity. Industrial leak and process monitoring.
Optical method Gas, liquid Very high selectivity and sensitivity, wide dynamic range, long lifespan. High cost, complex instruments, may require specialized calibration. Trace analysis, environmental, and breath monitoring

Table 3.

The commonly used real-time NH3 measurement methods.

Chemical and colorimetric methods rely on reactions that produce a measurable color change, such as those used in test papers, sulfur sticks, Nessler’s reagent, the indophenol blue method, and colorimetric film sensors. These approaches are typically simple, low-cost, and suitable for rapid screening or qualitative detection of high NH₃ concentrations, such as the AMoN mentioned above in Section 2.2.

Electrochemical sensors determine NH₃ concentrations by converting electrochemical reactions into electrical signals. Ammonia diffuses into the sensor and undergoes oxidation or reduction, generating a current proportional to its concentration. These sensors are compact, energy-efficient, and relatively inexpensive, offering good linearity and specificity to NH₃, although they may exhibit cross-sensitivity to other gases. Electrochemical (EC) sensors are widely used in portable and stationary gas detectors for real-time air-quality and occupational safety monitoring.

Semiconductor, or metal-oxide-semiconductor (MOS), sensors measure changes in electrical resistance caused by the adsorption of gas molecules on a metal oxide surface. MOS sensors are simple, durable, and low-cost, making them widely used in industrial applications. However, they typically exhibit lower selectivity and sensitivity (parts per million by volume (ppmv) level or higher) compared with other methods and often require elevated operating temperatures.

Among all approaches, optical techniques [33–35] are the most sensitive and reliable for NH₃ detection. These advanced methods use light absorption or scattering to quantify ammonia with high sensitivity and selectivity. A detailed description and inter-comparison of optical instruments are presented in Section 3.3.

Among the four main categories of NH₃ monitoring technologies, chemical and optical instruments offer the highest sensitivity, capable of detecting atmospheric ammonia at sub-pptv (parts-per-trillion by volume) levels with response times ranging from milliseconds to minutes [33–35]. To date, numerous instruments have been developed for pptv–ppmv NH₃ detection across various temporal resolutions. These include wet-chemical analyzers such as the annular rotating batch denuder (RBD), annular denuder sampling with online analysis (AMANDA), and AiRRmonia (an advancement of the AMANDA system); laser-based techniques such as quantum cascade laser absorption spectroscopy (QCLAS), including its dual-channel (DUAL-QCLAS) and compact (c-QCLAS) configurations; photoacoustic spectroscopy (PAS) [36–38], including microphone-based PAS [36, 37] and quartz-enhanced PAS (QEPAS) [38]; and other advanced optical and mass spectrometric methods, including cavity ring-down spectroscopy (CRDS) [33–35, 39], cavity-enhanced absorption spectroscopy (CEAS) [40], chemical ionization mass spectrometry (CIMS) [27, 28], ion mobility spectrometry (IMS) [33], mini differential optical absorption spectroscopy (MiniDOAS) [35, 41], gas chromatography (GC) [42], and open-path Fourier transform infrared spectroscopy (OP-FTIRS) [43].

Because NH₃ is highly adhesive and reactive, instead of closed-path QCLAS [44], open-path configurations are often employed in QCLAS, CRDS, DOAS, and FT–IR systems to minimize sampling losses and enhance measurement accuracy. The performance characteristics of these NH₃ measurement techniques are summarized in Table 4. Based on specific monitoring objectives, the most suitable instruments can be selected for individual applications. Table 5 presents representative NH₃ concentrations observed worldwide using these instruments across various environmental conditions and national monitoring standards.

Instrument Manufacturer Air flow rate [lmin-1] Time resolution/time average [s] Precision [ppbv] Range [ppbv] Accuracy [%] [References]
RBD Energy Research Foundation of the Netherlands (ECN) 27 2400/3600 0.02 Not specified Not specified [33]
AMANDA 28 450/450 0.02 0.02–500 Not specified [33]
AiRRmonia R&R Mechatronics 1 600/60 0.05 0.04–500 ±31 [33]
DUAL-QCLAS Aerodyne Research, Inc. (ARI) 15 0.2/60 0.018 Not specified ±52 [33]
c-QCLAS 8.9 1/60 0.05 Not specified ±101 [33]
PAS:WaSul-Flux Hilase Ltd. 4 300–1800/300–1800 0.25 0.25–1,000,000 Not specified [33]
PAS:Nitrolux-100 Pranalytica Inc. 1.2–1.6 3/300 0.1 0.1–200 ±43 [33]
CRDS, EnviroSense 1000 Analyzer Picarro Inc., USA 1 3/300 0.07 0.07–25 ±73 [33]
CRDS, Tiger-i 2000 Tiger optics, USA 0.48 1 0.83 0–20,000 ±4 [35]
CIMS Georgia Institute of Technology CIMS Team 19.5 1/60 0.94 Not specified ±44 [33]
IMS Bruker Daltonik 0.4 4/60 Not specified Variable Not specified [33]
CEAS: AP2E AP2E, France 1.0 60 10 0–10,000 n/a [35]
PAS: LSE LSE monitors, NL 0.1 60 n/a 0–40,000 n/a [35]
PAS: TGA300 series Omnisens S.A., Switzerland ≤5 3 0.1 0.1–3,000 0.25 or 1% [36]
QEPAS Shanxi University 0.26 0.3/52 2.2/0.09 0–10,000 n/a [37]
CEAS: LGR Los Gatos Research (LGR) Inc., USA 0.25 1 < 1.5 at 1 s 0.5–10,000 n/a [35]
GC TU Delft 0.0014 <300 150 100–25,000 n/a [42]
OP-FTIRS MIDAC Corp. n/a 8/120 Not specified Not specified Not specified [33]
OP-miniDOAS RIVM, NL/NTB, Buchs, CH n/a 60 0.36 0.36–430 2 [35]
OP-CRDS Colorado State University n/a 3 0.6 0–500 n/a [45]
Open-path NH3 Analyzer Healthy Photon Co., China n/a 0.1 <0.3 0–2000 n/a [46]
OP-QCLAS Princeton University n/a 0.1 0.2 0–10,000 ±20% [47]

Table 4.

Summary of the characteristics of the instruments.

Notes: RBD: annular rotating batch denuder, AMANDA: annular denuder sampling with online analysis, AiRRmonia: an advancement of the AMANDA system; QCLAS: laser-based techniques such as quantum cascade laser absorption spectroscopy, DUAL-QCLAS: dual-channel QCLAS, c-QCLAS: compact QCLAS, PAS: photoacoustic spectroscopy, QEPAS: quartz-enhanced PAS, CRDS: cavity ring-down spectroscopy, CIMS: chemical ionization mass spectrometry, IMS: ion mobility spectrometry, CEAS: cavity-enhanced absorption spectroscopy, MiniDOAS: mini differential optical absorption spectroscopy, GC: gas chromatography, OP: open-path, FTIRS: Fourier transform infrared spectroscopy.


Locations Type Period NH3 (ppb) Methodology
Shanghai Urban 2013.7–2014.9 6.2 ± 4.6 DOAS
China Rural 2013.7–12, 2014.3–6 12.4 ± 9.1 MARGA
Industrial 2014.1–6 17.6 ± 9 DOAS
Beijing Urban 2007.1.23–2.14 7.21 ± 4.94 Aunular denuder
China 2007.8.2–31 33.46 ± 9.11
Beijing Urban 2008.2–2010.7 22.8 ± 16.3 Passive sampler
China Rural 2007.1–2010.7 10.2 ± 10.8
North Plain, China Rural sites, suburban 2008.8–2009.9 20.6 Passive sampler
Kanpur Urban 2007.4.8–6.30 23.7 ± 5.1 Online NOx–NH3
India 2007.12.1–2008.1.31 21.5 ± 6.6 Analyzer
Seoul Urban/GJ 2010.9.1–2011.8.23 10.9 ± 4.25 WS-CRDS
Korea Urban/GS 12.3 ± 4.23
Lahore, Pakistan Urban 2005.12–2006.2 30.3–116.9 Aunular denuder
Taiwan Industrial 2003.9–2004.12 100.2 (Neipu)72.8 (Pingtung)84.9 (Pingtan) Passive sampler
USA Urban/Atlanta 2007.7–12 1.35 ± 1.19 Citric acid denuder
Rural/Georgia 3.32 ± 2.37 Difference technique
Houston, TX Urban 2010.2.12–3.1 2.42 ± 1.16 EC-QCL-based
USA 2010.8.5–9.25 3.07 ± 2.87 sensor
Wisconsin Urban 2009.1.1–3.31 2.3 iCAMs
USA Rural 2.4
USA Forest/Brent 2013.6.1–7.15 1–2 CIMS
Urban/Kent 2013.8.31–9.20 Up to 6
Ontario, Canada Rural 2010.3.30–2011.3.29 4.71 Passive sampler
Vredeped, Netherlands Rural 2009.12.16–2010.2.18 Up to 197.6 DOAS
Barcelona Urban BC 2011.5.6–9.7 2.9 ± 1.3 Online instrument
Spain Urban CC 2011.5.13–6.28 7.5 ± 2.8

Table 5.

Typical atmospheric NH3 concentration observed by various instruments at different global locations in different countries [2].

WS-CRDS: wavelength-scanned cavity ring-down spectroscopy; EC-QCL: external-cavity quantum cascade laser; iCAMS: inorganic continuous aerosol measurement system; CIMS: chemical ionization mass spectrometer.


In summary, satellite data provide broad and repeatable coverage for observing large-scale patterns, identifying hot spots, and tracking long-term trends. When combined with atmospheric transport models, it can generate top-down estimates of NH₃ emissions, which can help validate or improve bottom-up emissions inventories. In contrast, in-situ measurements provide highly accurate, real-time data at specific locations, offering high precision, fine temporal resolution, direct surface-level measurement, and the ability to validate remote sensing data and model outputs. Among the various in-situ measurement methods – chemical, electrochemical, semiconductor, and optical techniques – chemical and optical methods offer the best sensitivity and selectivity. However, for closed-cell configuration instruments of both chemical and optical methods, their precision and accuracy can be affected by adsorption/desorption and artificial losses, instrument interference, calibration challenges, and signal attenuation in eddy covariance systems. Open-path laser spectroscopy sensors provide the most reliable option for real-time, precise, and robust NH₃ measurements, especially for eddy covariance flux measurement.

3.3 Open-path optical spectrometers for eddy covariance flux measurement

Among the various instruments summarized above, open-path quantum cascade laser absorption spectroscopy (OP-QCLAS) offers distinct advantages for atmospheric in-situ measurements by eliminating sampling biases and time delays inherent to closed-path systems [48, 49]. This technique measures gas concentrations directly in the open air along the optical path, making it well-suited for deployment on aircraft [47, 50], unmanned aerial vehicles, and mobile laboratory platforms for accurate NH₃ monitoring [50–53]. Compared with open-path MiniDOAS and FTIR systems, OP-QCLAS provides true “point-source” detection capability, achieving sub-pptv precision and temporal resolution better than 0.1 s [54–56].

These characteristics of the open-path laser spectroscopy sensor make it an ideal instrument for high-resolution spatiotemporal NH₃ measurements, particularly in eddy covariance applications. Recent advancements in NH₃ flux measurements using the eddy covariance method – including instrumentation, time resolution, and detection limits – are summarized in Table 6.

Era [references]Instrumental techniquePathKey advancementsTime resolutionDetection limit
Early studies (Pre-2010s) [57] Tunable diode laser absorption spectrometers (TDLAS) Closed path Use heated or inert-coated inlets to reduce adsorption effects. ~10 Hz, but often with an attenuated signal due to inlet losses. ~5 ng m⁻2 s⁻1 flux.
2010s[58, 59] Quantum cascade laser (QCL) spectrometers Closed path Better sensitivity and precision incorporated hydrophobic coatings and heated cells to further minimize NH3 Adsorption. ~10 Hz, but still required corrections for high-frequency signal loss. Low ppbv concentration limits, leading to improved flux detection limits.
2010s, 2020s [28, 59, 60] Chemical ionization mass spectrometry (CIMS) Closed path Used electron transfer reaction ionization to measure NH3 Fluxes. ~1 second effective time resolution. Sub-ppbv for concentration; ~5 ng m⁻2 s⁻1 for flux.
Mid-2010s [55, 61] Open-path QCL spectrometers Open path Elimination of inlet-based adsorption issues by measuring NH3 directly in open air. 10 Hz. Concentration:0.30 ppbv;Flux: 1.3 ± 0.5ng m⁻2 s⁻1(for 30-minute intervals).
Recent advances(2020s)[49, 50, 52–56] Portable, low-power open-path QCLs;open-path MiniDOAS Open path Further reduction in size, power consumption, and weight. 10 Hz. Concentration:~0.30 ppbvFlux: 7.1 ± 1.1g N m⁻2 h⁻1(for 30-minute intervals).
Future development[62] Next-generation open-path spectrometers Open path Real-time spectroscopic effect correction and more robust optical components. Potential for simultaneous measurement of multiple trace gases. 10 Hz. Concentration:0.2 ppbv for NH3Flux:<1 ng m⁻2 s⁻1.

Table 6.

Summary of instrumental progress for ammonia eddy covariance flux measurements.

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4. Strategies and policies for ammonia mitigation

Because of the critical implications of atmospheric NH₃ for human health and environmental resilience, effective mitigation strategies and regulatory policies are essential [62–65]. Various efforts must primarily target the dominant emission sources – agriculture and industry. Agricultural mitigation focuses on best management practices, optimized fertilizer application, and dietary adjustments for livestock, whereas industrial mitigation emphasizes advanced emission capture technologies and the transition to cleaner energy systems [66, 67]. At both international and national levels, policies establish emission reduction targets and encourage the adoption of innovative technologies. Several effective strategies and initiatives have been implemented to reduce NH₃ emissions from agricultural and industrial sectors. A summary of these mitigation approaches, technologies, and policy frameworks is provided in Tables 7, 8, and 9.

Strategy type Description Specific actions
Feed management Balancing animal diets to reduce excess nitrogen excretion, which is a key source of ammonia. Reduce crude protein levels in livestock diets to better match an animal’s needs.
Manure handling and storage Managing manure to minimize the decomposition and volatilization of nitrogen into ammonia. Use covers for solid manure and slurry storage to reduce air contact.Separate urine and feces using specific barn flooring designs.Acidify slurry to lower its pH and inhibit ammonia release.Add chemical amendments such as alum or biochar to manure to bind nitrogen.
Manure and fertilizer application Optimizing the application of manure and fertilizers to increase nutrient uptake by crops and decrease emissions. Incorporate manure into the soil quickly after spreading. Use low-emission slurry spreading equipment, such as trailing hoses or injection systems, instead of splash plates.Use nitrogen inhibitors with urea-based fertilizers to slow nitrogen loss.Use soil analysis and management plans to avoid over-fertilization.
Air treatment Capturing and treating ammonia in the exhaust air from animal housing facilities. Install air scrubbers or biofilters in buildings to remove ammonia from exhaust air.

Table 7.

Strategies focus on reducing ammonia emissions throughout the farming cycle, from livestock diets to manure application [67–70].

Technology Description Advantages and applications
Ammonia stripping Forcing air or steam through wastewater at a high pH to convert ammonium to ammonia gas, which is then captured. Cost-effective and relatively simple for treating high-ammonia wastewater streams.
Adsorption Using porous materials such as zeolite or activated carbon to bind and remove ammonia molecules from wastewater. Can be highly effective and reversible, though stability and efficiency are influenced by the operating conditions.
Membrane filtration Employing semi-permeable membranes to filter and concentrate ammonia in wastewater, this process can be paired with other systems for recovery. Can achieve high removal rates with low energy consumption and without chemicals, though membrane fouling can be an issue.
Biological systems Using biological processes such as nitrification, denitrification, or anaerobic digestion to convert ammonia into less harmful nitrogen compounds. An environmentally friendly, cost-effective option for wastewater treatment.

Table 8.

Innovative techniques are available for treating wastewater and industrial gas streams to remove or recover ammonia [66, 73–75].

Policy or regulation Area Key provisions
Gothenburg Protocol (UNECE) International (Parties to the Convention on Long-Range Transboundary Air Pollution) Sets NECs for various air pollutants, including ammonia, with reduction commitments for signatory countries. Requires countries to establish national codes of good agricultural practice to control ammonia emissions.
NECs Directive (EU) European Union (EU) Sets legally binding emission reduction commitments for EU member states for ammonia and other air pollutants, with targets for 2020 and 2030.
Common Agricultural Policy (EU) European Union (EU) Influences farm-level practices that can impact ammonia emissions by linking farm payments to environmental regulations.
Clean Air Act (CAA) (USA) United States (federal level) Provides federal authority to regulate emissions. While ammonia reporting exists, a comprehensive regulatory approach to agricultural emissions is still evolving.
Risk Management Plan (RMP) (EPA) United States (EPA) Requires facilities handling more than a threshold quantity of certain toxic substances to implement a chemical accident program and submit a plan to the EPA. However, agricultural nutrients are often excluded.

Table 9.

Governments and international bodies have implemented policies to reduce ammonia emissions, often focusing on the agriculture sector [67, 75, 77, 78].

As an example, for the strategy of manure handling and storage, the synthesized literature results [71] show that NBPT + NPPT reduced NH₃ loss by 75% (95% CI: 58–82%, n = 32), 2-NPT by 70% (95% CI: 63–76%, n = 19), and NBPT by 61% (95% CI: 57–64%, n = 165), giving an average reduction of 69% across these three urease inhibitors. In contrast, MIP slightly increased NH₃ loss by 0.3% on average (95% CI: − 8–9%, n = 40). These findings broaden our understanding of urease inhibitor efficacy under field conditions and highlight that not all products perform equally in reducing NH₃ emissions in practice.

Another study [72] showed that acidification is an effective and promising abatement technique to significantly reduce NH₃ emissions. By retaining more nitrogen in the manure, manure acidification increases the amount of plant-available nitrogen during land application. Ammonia emissions decreased by 77 ± 11% in housing, 63 ± 30% during storage, and 43 ± 18% after field application of acidified slurry. On average, NH₃ emissions were reduced by 60 ± 28% across all manure management stages.

Compared with traditional methods, these newer technologies [66, 73–75] offer several advantages, including lower energy consumption, reduced chemical use, and lower operating costs, along with the potential to recover valuable by-products such as fertilizers or renewable fuels. However, there are also potential challenges and considerations, including economic viability, technical maturity and validation, market suitability of the products, operational complexity, and the need for adaptation and adoption.

Governments and international organizations have introduced a range of policies to mitigate ammonia emissions, primarily targeting the agricultural sector (see Table 9). A review of these efforts reveals both meaningful progress and ongoing challenges. Successful outcomes are generally linked to well-designed, science-based interventions that integrate technical innovation with practical implementation. However, persistent difficulties arise from competing environmental and economic priorities, the financial burden placed on farmers, and the structural and behavioral complexity of agricultural systems. These findings underscore the need for more coherent, incentive-driven policy frameworks that balance environmental goals with agricultural productivity and socio-economic sustainability.

The European Union (EU) [76–80] has established legally binding commitments to reduce ammonia (NH₃) emissions, requiring a 19% reduction by 2030 relative to 2005 levels. While these obligations are implemented through national legislation, the specific reduction targets vary among member states depending on country-specific conditions and policy frameworks. The principal regulatory instrument governing NH₃ emissions is the National Emission Ceilings (NEC) Directive (2016/2284/EU), which outlines two phases of binding reduction commitments based on 2005 baseline levels.

During the 2020–2029 period, the Directive [76–80] mandates an EU-wide average reduction of 6%. A 2024 progress report indicated that overall EU emissions had already declined by 17% between 2005 and 2023, thereby surpassing the collective target, although several member states did not achieve their individual ceilings. From 2030 onward, the Directive stipulates a more ambitious 19% average reduction requirement, reflecting the EU’s long-term strategy for mitigating agricultural air pollution and promoting sustainable nitrogen management.

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5. Conclusions and outlooks

Atmospheric ammonia (NH3) poses significant risks to air quality, ecosystems, and human health, primarily through its contribution to the formation of fine particulate matter (PM2.5). The predominance of agricultural emissions underscores the complexity of managing NH3 within both environmental and socio-economic systems. This review highlights recent advances in identifying emission sources, improving measurement precision, and developing mitigation strategies. Despite substantial progress in in-situ, remote-sensing, and sensor-based monitoring technologies, accurately quantifying NH₃ remains challenging due to its high reactivity, low ambient concentrations (pptv to ppbv), and pronounced spatiotemporal variability.

The outlook for NH3 emission research, measurement, and policy reflects growing global concern over its environmental and health impacts. Key drivers include the expansion of agricultural production, increasing urban vehicle emissions, and the emergence of green ammonia as a potential clean fuel. These developments highlight the urgent need for precise measurement techniques and robust, internationally coordinated mitigation frameworks. Current research priorities focus on urban emission dynamics, declining acid gas concentrations, climate change feedbacks, and integrated modeling approaches.

Future research should prioritize the enhancement of in-situ and satellite-based observation systems to enable continuous, high-resolution monitoring, thereby refining emission inventories – particularly in regions with limited measurement capacity. Continued innovation in low-cost, durable sensors will be essential for long-term agricultural monitoring. Advances such as expanded ground-based networks, next-generation emission models, and high-resolution urban studies will further strengthen understanding and policy evaluation. Moreover, integrated atmospheric models that couple meteorological factors, climate drivers, and co-pollutant interactions are crucial for improving predictive capacity.

Effective NH3 mitigation will rely on the coordinated application of advanced technologies, sustainable agricultural practices, and enforceable policy instruments. Key strategies include reducing agricultural emissions, leveraging trade and supply networks, transitioning toward clean ammonia production, and adopting holistic approaches that incorporate carbon accounting and life-cycle assessment. As emissions continue to rise globally – particularly in developing regions – international collaboration will be critical to implementing cost-effective and context-appropriate solutions. Strengthening the scientific understanding of the links between agricultural NH3, secondary aerosol formation, and human health impacts will further underscore the urgency of comprehensive global regulation and concerted action.

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Acknowledgments

We gratefully acknowledge the invitation from IntechOpen and other supporters for this book chapter.

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Written By

Hongming Yi

Submitted: 06 October 2025 Reviewed: 30 October 2025 Published: 07 January 2026

© 2026 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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