Nitrous acid (HONO) plays a crucial role in atmospheric chemistry as a precursor for hydroxyl radicals, which control air quality and climate through oxidation of greenhouse gases and formation of ozone and aerosols. Recent research has identified soil emissions as a significant but poorly quantified source of atmospheric HONO (7.4–12.0 Tg-N y⁻¹ globally), with ammonia-oxidizing bacteria (AOB) identified as the primary biogenic source. Despite this breakthrough in understanding the mechanistic basis of soil HONO production, major knowledge gaps remain regarding temporal and spatial variability of these emissions. Current global estimates are based on limited datasets, primarily from short-term controlled studies, leaving substantial uncertainties about how environmental factors drive real-world emission patterns across different ecosystems and seasons.
This PhD project will address these critical gaps through systematic field measurements across representative UK ecosystems over complete annual cycles. The research will establish 6 long-term monitoring sites spanning grassland, cropland, deciduous forest, coniferous forest, urban green space, and wetland environments. Seasonal flux measurements using chamber-based systems will quantify HONO emissions alongside comprehensive environmental characterisation including soil temperature, moisture, pH, nitrogen availability, and ammonia-oxidiser community structure. The spatial component will involve high-resolution mapping along urban-rural gradients and detailed emission surveys across landscape mosaics to identify hotspots and develop emission factors for different land use types. This multi-scale approach will bridge the gap between mechanistic understanding and landscape-scale patterns needed for atmospheric modelling applications.
Statistical and machine learning approaches will be used to develop predictive models linking environmental variables to HONO emissions. These models will be validated against independent datasets and applied to estimate regional-scale emissions using existing soil and climate databases.
Expected outcomes include the most comprehensive dataset of soil HONO measurements to date, validated predictive tools for atmospheric chemistry models, and improved understanding of environmental controls on soil-atmosphere nitrogen exchange. The research will directly support enhanced air quality modelling, better quantification of soil-atmosphere feedbacks in Earth system models, and evidence-based land management strategies for atmospheric chemistry impacts.
This project is not suitable for CASE funding
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The project employs established field measurement techniques combined with systematic experimental design to characterise HONO emission patterns. Static chamber methods using 10L Teflon chambers with ICAD (Iterative Cavity Enhanced DOAS) detection will quantify fluxes at seasonal intervals across six ecosystem types over complete annual cycles. Spatial variability will be assessed through systematic transect measurements and high-resolution mapping using portable flux systems. Supporting measurements include soil chemical analysis (ion chromatography, pH, C/N), microbial quantification (qPCR for AOB/AOA genes), and comprehensive environmental monitoring (temperature, moisture, nitrogen availability). Controlled manipulation experiments will test responses to key environmental drivers including temperature, moisture, and nitrogen addition. Statistical modelling approaches including multiple regression, random forest, and machine learning techniques will develop predictive relationships between environmental variables and HONO emissions. Model validation will use independent datasets from literature and collaborative sites, with sensitivity analysis to identify key uncertainties. Regional extrapolation will apply validated models to existing soil and climate databases for landscape-scale emission estimates.
DRs will be awarded CENTA Training Credits (CTCs) for participation in CENTA-provided and ‘free choice’ external training. One CTC can be earned per 3 hours training, and DRs must accrue 100 CTCs across the three and a half years of their PhD.
The DR will develop expertise in trace gas measurement techniques, environmental analytical chemistry, and statistical modelling. Technical skills include chamber-based flux measurements, advanced gas detection systems (ICAD), soil chemical analysis, and molecular microbiology techniques (qPCR). Data analysis training encompasses R/Python programming, multivariate statistics, machine learning applications, and model validation approaches. Professional development includes project management of multi-site field campaigns, collaboration with atmospheric modelers and soil scientists, and science communication for policy applications. The research provides excellent preparation for careers in environmental consulting, air quality modelling, climate research, or academic positions in atmospheric or soil science.
The project will involve collaboration with the UK Centre for Ecology & Hydrology (UKCEH), a CENTA Research Centre partner. Dr. Niall McNamara from UKCEH will serve as Co-I, bringing expertise in landscape-scale biogeochemical processes and access to established monitoring networks. This collaboration will enable integration with existing CEH analytical capabilities and long-term field sites, enhancing spatial coverage and providing opportunities to leverage ongoing environmental monitoring programmes. The partnership strengthens the project’s capacity to scale findings from plot-level measurements to landscape applications, directly supporting the development of regional emission models for atmospheric chemistry research.
Year 1: Site establishment and method validation; begin seasonal monitoring campaign; establish quality control protocols; first conference presentation on preliminary findings
Year 2: Complete spatial mapping studies and process manipulation experiments; analyze first year’s seasonal data patterns; begin model development; submit first manuscript on seasonal emission patterns
Year 3: Model development and validation; regional extrapolation studies; complete dataset analysis; thesis writing and final manuscript submissions; present findings at international conferences
Mushinski, R.M., et al. (2019). Microbial mechanisms and ecosystem flux estimation for aerobic NOy emissions from deciduous forest soils. Proceedings of the National Academy of Sciences, 116(6), 2138-2145.
Oswald, R., et al. (2013). HONO emissions from soil bacteria as a major source of atmospheric reactive nitrogen. Science, 341(6151), 1233-1235.
VandenBoer, T.C., et al. (2013). Understanding the role of the ground surface in HONO vertical structure: High resolution vertical profiles during NACHTT-11. Journal of Geophysical Research: Atmospheres, 118, 10,155–10,171.
For any enquiries related to this project please contact Dr Ryan Mushinski, Ryan.M[email protected], Lab website: www.ryanmushinski.com.
To apply to this project:
Applications must be submitted by 23:59 GMT on Wednesday 7th January 2026.