Feature Scoping Study: On Track of NH3

Cross-validation of satellite and ground-level measurements

Each month we highlight one of our Scoping Studies, each funded through our Collaboration Building Workshops. This month we welcome a blog post from Dr Anna Font (Imperial College London), who is working with STFC colleagues in RAL Space and the Hartree Centre to improve our understanding of ammonia concentrations through satellite and ground-level measurements.

Ammonia (NH3) is mostly emitted to the atmosphere from agricultural and farming activities including the use of fertilizers, manure, cattle and dairy farming, among others. NH3 is an important precursor of fine particles due to its reaction with available acids (i.e. nitric and sulfuric acid) to form ammonium nitrate and ammonium sulphate. Airborne fine particles are a significant human health thread and are associated with cardiovascular and respiratory diseases. Further, gaseous ammonia and ammonium compounds are deposited into the ecosystems damaging sensitive habitats. In the UK, agricultural activities represent more than 80% of the atmospheric ammonium emissions and there are no regulations in place to limit these emissions. The Clean Air Strategy published in 2018 aims to reduce NH3 emissions in the UK making available a code of good agricultural practice (COGAP).

Hotspots of ammonia have been identified by means of satellite measurements from both CrIS and the IASI instruments onboard the Suomi NPP and MetOp satellites, respectively. In Europe these include areas in the UK and neighbouring countries such as France, Belgium and The Netherlands. NH3 emissions from agricultural fields in north-west Europe have been associated with particle episodes which accumulate on a regional scale especially during springtime in south-east England. In the UK, hotspots of NH3 are observed in the intense agricultural regions in southern England. 

In the UK, a network of 85 sites distributed in the country have been measuring ammonia at the surface level since mid-1990s. Despite the network provides a good coverage of the UK land, there is a large heterogeneity of concentrations related to the large variation in emission sources at ground level as it can be seen in Figure 1. Concentrations are reported as monthly means. Recently, on-line concentrations of NH3 are available at two rural locations in the country comprising one agricultural site in Scotland and one in south-east England; and also in urban areas comprising London, Manchester and Birmingham. On-line techniques report high time resolve data of NH3 concentrations, usually at hourly basis.

Figure 1. Monthly concentrations of NH3 gas as measured by the Defra UKEAP National Ammonia Monitoring Network in 2019. Only active samplers (delta) are shown in this graph. Data from UK-air website.

Satellite observations are column-integrated and have larger footprints compared to the ground-level measurements. Little is known if satellite retrievals of NH3 concentrations are representative of ground-level measurements in the UK and how they are related. Despite the mistime and misdistance errors which are introduced by comparing measurements of a very reactive species such as NH3 that are not perfectly collocated in time and space, such comparison of column-integrated and ground-level measurements is still important to validate satellite products.

The SAQN workshop on last autumn 2020 was the perfect platform to establish collaboration links between scientists working with satellite data, in-situ observations and big data specialists. The project is establishing links between STFC RAL space, STFC Hartree Centre and Imperial College London. With this project we are aiming to evaluate the ability of satellite observations of NH3 to reproduce temporal variability of surface air concentrations across the UK to before estimate long-term changes in air pollution to assess the efficacy of air quality policies in recent years. The integration of satellite data and ground-level measurements will help us identify hot-spots of NH3 in the UK and monitor possible changes over time.

Featured Scoping Study: AIREFUNITS

Our guest blog this month details the AIREFUNITS project, a collaboration between Coventry University, University of Cambridge and STFC’s RAL Space.

Attention is increasingly being paid globally to the air quality state in regions where continuous air quality monitoring devices hardly exist. This lack of infrastructure is mainly because the resources to acquire such monitoring equipment are lacking, especially in regions such as sub-Saharan Africa, where over 1.1 billion people are affected.

The data acquired so far from these regions indicate the presence of poor air quality levels and the need to devise intervention measures to improve the air quality and reduce the resultant health and socio-economic consequences. However, due to their paucity of resources, these regions largely lack robust reference air quality monitoring units that are used to underpin the data collected from diverse low- and medium-cost monitoring units that many use in these areas. These reference units are essential as we need confidence in the air quality data collected from these monitoring units to formulate the appropriate intervention policies.

This issue was addressed at the recent SAQN collaboration building workshop, and researchers from Coventry University, the University of Cambridge and STFC RAL Space were funded to investigate the development of a portable reference/calibrating unit for air quality sensor networks.

The AIREFUNITS project will utilise the STFC RAL Space Spectroscopy Group’s capability for developing cost-effective, highly sensitive, reliable, portable laser-based gas sensors.

This study will advance the development of a robust portable reference air quality unit that can be used to calibrate the various monitoring units in these low-resource regions, thus enabling the construction of effective intervention measures to mitigate the impacts of poor air quality.

THE AIREFUNITS TEAM:

Dr Nwabueze Emekwuru, Coventry University. Dr Lekan Popoola, University of Cambridge. Dr Thomas Wall, STFC RAL Space.

Featured Scoping Study: Emulating the Chemical mechanism through Machine Learning to speed up the real time Air Quality Prediction (ECheMLAQ)

This month we welcome a guest blog from a team using STFC expertise in Machine Learning to improve Air Quality Forecasting Systems. The scoping study is led by Dr Pushp Raj Tiwari.

Air Quality Forecasting Systems (AQFS) have an integrated chemistry module and simulations through them are computationally very expensive. Here we demonstrate the concept of replacing one module from CTMs with a novel Machine Learning (ML) framework to achieve orders of magnitude speed up in chemistry simulations, which mostly through traditional methods are slow and tend to suffer from numerical instability.

The recent SAQN workshop provided a unique opportunity to collaborate and address this problem. The three experts* from different organisations will be developing and investigating the potential for Machine Learning to reproduce the behaviour of a chemical mechanism, yet with reduced computational expense by working closely with each other.

In the period of January to June 2021, this pilot study aims to:

  • Develop the ML algorithm and test it against the model generated result
  • Replace the chemical mechanism with ML and perform simulations

The ML technique developed and results from this initial study will be used as proof of concept to allow this group to continue developing the next generation Air Quality Forecasting Systems (AQFS). Once the ML based system is sufficiently developed, it will enable scientists and prediction centres to implement it in their AQFS and achieve orders of magnitude speed up in prediction with reduced computational time and cost.

* Dr. Pushp Raj Tiwari, Centre for Atmospheric and Climate Physics Research, University of Hertfordshire; Dr. Vera He, UK Centre for Ecology and Hydrology, Dr. Barry Latter, STFC.

Guest blog: Modular Relaxed Eddy Covariance sensor for Air Quality – MOREC-AQ

Our featured Scoping Study this month is from the team led by Dr Lekan Popoola, examining the relationship between ammonia (NH3) and particulate matter (PM).

The Clean Air Strategy (Defra, 2019) sets out an ambitious, stringent target to cut emission of major air pollutants by 2020 and 2030. A significant air pollution challenge is the shift in the relative importance from a relatively small number of major emission sources to many minor sources (such as intensive agriculture, wood burning from homes and smaller industrial sites). The impact of COVID-19 restrictions and various lockdowns have created changes in mobility behaviour, with increasing importance of residential emissions as many of us work from home. Evaluation of the impact of these emission sources requires evidence-based scientific methods and data.

During the recent SAQN collaboration building workshop, research scientists from STFC-RAL Space (Thomas Wall), Cranfield University (Zaheer Nasar), and the University of Cambridge (Lekan Popoola) were successful in getting funding from SAQN to develop a proof-of-concept for a cost-effective Modular Relaxed Eddy Covariance (MOREC-AQ) measurement approach to fluxes/source characterisation and a miniaturised cost-effective NH3 instrument to incorporate into MOREC-AQ (see schematics below).

The specific objectives include: (1) feasibility studies for a portable high-resolution NH3 sensor; (2) design and characterisation of a prototype MOREC-AQ unit; (3) explore additional funding opportunities to further develop and optimise the prototype MOREC-AQ unit.

Monitoring and quantifying atmospheric emissions and their drivers is important to investigate the interplay between gaseous pollutants and PM, informing and evaluating the impacts of air quality interventions. This proof of concept study will allow scoping out the development of cost-effective, reliable emission monitoring solutions for air quality management, particularly in the context of the NH3/PM relationship.

System schematics for the MOREC-AQ

If you have comments or questions about this project, you can share them on our discussion board.

Guest Blog – Sources, behaviour and mitigation strategies influencing indoor air quality: A pilot study

Each month, we welcome a guest blog post from one of our current Scoping Studies, funded through our recent Collaboration Building Workshop. This month we’re pleased to hear from a team examining different influences on indoor air quality.

The average person in the UK spends more than 90% of their time indoors, and indoor air quality (IAQ) related emissions can contribute significantly to total air pollution exposure. Despite this, relatively few studies focus on IAQ compared to outdoor air quality. 

A recent SAQN workshop brought together experts on building design and ventilation, indoor air quality measurement, occupant behaviour, and computational fluid dynamics (CFD). The 9 experts* from academia and industry will be utilising the domestic energy systems and technologies incubator based at The University of Chester (designed to represent a kitchen space), to characterise IAQ related events using equipment donated by the participating organisations.

In the period of January to June 2021, this pilot study aims to:

  • Define occupant behaviours (e.g., cooking, cleaning, etc) based on the UK Time Use Survey.
  • Carry out physical behaviours in different ventilation conditions, e.g. cooking & cleaning.
  • Measure air quality factors (including particulates and microbes) and relevant environmental factors (e.g., temperature and air movement) before and after the activities occur.
  • Develop a CFD simulation and utilise STFC high performance computing facilities to improve its relationship to actual data. 

The data from this initial study will be used as proof of concept to allow this group to continue developing and validating the CFD simulation against physical results, as well as to facilitate future deployments into real-world indoor environments. Once the CFD simulation is sufficiently developed, it will enable faster exploration of many behavioural activities and environmental settings.

If you have comments or questions about this project, you can share them on our discussion board.

* Dr Vicki Stevenson, Cardiff University; Dr Archit Mehra, University of Chester; Dr Zaheer Nasar, Cranfield University; Dr Stefano Rolfo, STFC; Dr Stephanie Gauthier, University of Southampton; Dr Alejandro Moreno Rangel, Lancaster University; Dr Jo Zhong, Nottingham Trent University; Dr Rob Ferguson, University of Essex; Dr Douglas Booker, NAQTS