Exploiting satellite measurements to reduce uncertainties in UK bottom-up NO<sub>x</sub> emission estimates

Abstract

Abstract. Nitrogen oxides (NOx, NO+NO2) are potent air pollutants which directly impact on human health and which aid the formation of other hazardous pollutants such as ozone (O3) and particulate matter. In this study, we use satellite tropospheric column nitrogen dioxide (TCNO2) data to evaluate the spatiotemporal variability and magnitude of the United Kingdom (UK) bottom-up National Atmospheric Emissions Inventory (NAEI) NOx emissions. Although emissions and TCNO2 represent different quantities, for UK city sources we find a spatial correlation of ~0.5 between the NAEI NOx emissions and TCNO2 from the high-spatial-resolution TROPOspheric Monitoring Instrument (TROPOMI), suggesting a good spatial distribution of emission sources in the inventory. Between 2005 and 2015, the NAEI total UK NOx emissions and long-term TCNO2 record from the Ozone Monitoring Instrument (OMI), averaged over England, show decreasing trends of 4.4 % and 2.2 %, respectively. Top-down NOx emissions were derived in this study by applying a simple mass balance approach to TROPOMI observed downwind NO2 plumes from city sources. Overall, these top-down estimates were consistent with the NAEI, but for larger cities such as London and Manchester the inventory is significantly (> 25 %) less than the top-down emissions. This NAEI NOx emission underestimate is supported by comparing simulations from the GEOS-Chem atmospheric chemistry model, driven by the NAEI emissions, with satellite and surface NO2 observations over the UK. This yields substantial model negative biases, providing further evidence to demonstrate that the NAEI may be underestimating NOx emissions in London and Manchester.

Satellite Data Applications for Site-Specific Air Quality Regulation in the UK: Pilot Study and Prospects

“…Few studies have focused on UK industrial point sources, and typically only large power stations such as Drax, the UK's largest NO 2 point source, are identified [38]. The majority of UK studies focus on combined source emissions over a large area, such as from large cities [22,25], or they investigate regional/national-scale changes [23,26]. In other countries with more favourable conditions, point source analysis has matured over the last 10 years.…”

“…Studies for government, such as the "Innovative technology to improve AQ monitoring" report for the Department for Environment, Food, and Rural Affairs (Defra) [18], the Highways England's "Strategy to improve air quality" [19] and the Scottish Government's "Clean air for Scotland strategy" [20], have identified satellite data products as a technology worthy of further investigation or implementation [21]. Defra are funding a project titled "Applying Earth Observation (EO) to Reduce Uncertainties in Emission Inventories", which has produced outputs demonstrating the potential of current satellites to validate UK National Atmospheric Emission Inventory (NAEI) for NO 2 and NH 3 [22,23]. The Scottish ClimateXchange Centre of expertise conducted a study, on behalf of the Scottish government, where satellite data was used to investigate urban and regional Scottish emission changes over time [24].…”

Identifying and accounting for the Coriolis Effect in satellite NO2 observations and emission estimates

“…New high-resolution instruments, such as the TROPOspheric Monitoring Instrument (TROPOMI), can resolve emission plumes from large industrial activities such as power generation, fabrication and refining processes (Anema, 2021;Goldberg et al, 2019;Ialongo et al, 2021;Wang et al, 2022). A suite of methods have been developed to derive emission estimates from both daily and time aggregated observations of these large sources (Beirle et al, 2011(Beirle et al, , 2019de Foy et al, 2015;Fioletov et al, 2015;Hakkarainen et al, 2021), providing a potential avenue for these instruments to assist with regulation and to constrain bottom up emission estimates (Marais et al, 2021;Pope et al, 2021;Potts et al, 2021). Emissions from these sources are often distinct, thermally buoyant and can extend over 0 -20 km vertically and 10 -200 km horizontally, where large scale atmospheric effects may progressively influence the dispersion and trajectory of the plume as it travels downwind.…”

Estimations of NOxemissions, NO2lifetime and their temporal variation over three British urbanised regions in 2019 using TROPOMI NO2observations

“…The work has focused on three large British cities: London, Manchester and Birmingham. While Pope et al (2022) [17] adapted the technique of Beirle et al (2011) [5] to estimate the NO x emissions in some UK cities, this work combines the EMG with a wind rotation technique (e.g. [18], [19]) to calculate NO x emissions with a similar method used by Fioletov et al (2015) [20] for SO 2 .…”

“…The rotation technique, where each pixel is rotated around the point source according to the wind direction so that all pixels appear to have the same wind direction, accumulates a statistically significant data set. The method presented in this study provides a unique emission estimate irrespective of the wind direction over the selected source regions unlike the estimates of Beirle et al (2011) [5] or those for the UK by Pope et al (2022) [17]. It also allows the use of a distinct calendar year of observation while Pope et al (2022) [17] needed to gather the observations during a longer period (Feb 2018-Jan 2020) to compare to a distinct National Atmospheric Emission Inventory (NAEI) reported year.…”