The Importance of Capturing Local Measurement-Driven Adjustment of Modelled

Hannah L. Walker, Mathew Heal, Christine Braban, Sarah R. Leeson, Ivan Simmons, Matthew R. Jones, Richard Kift, Nicholas Marsden, Marsailidh M. Twigg

Research output: Contribution to journalArticlepeer-review


Accurate photolysis rate constants are essential for simulation of local air quality but their values can vary substantially with changes in local meteorological and surface conditions. This study demonstrates the use of local radiometer measurements for capturing via hourly measurement-driven adjustment factors (MDAF) the temporal resolution needed to adjust clear-sky or cloud-free model
estimates of j(NO2). Measurements simultaneously at two sites in the UK (Auchencorth Moss and Manchester) showed that TUV (v5.3) model estimates of j(NO2)# in cloud-free conditions (used as an example of modelled j-values) were, on average, approximately 45% larger than measured j(NO2)#, which would lead to substantial model bias in the absence of local adjustment. At Auchencorth Moss, MDAF values based on 4π and 2π radiometer inlets generally agreed very well with each other (<6% average difference). However, under conditions of particularly high surface albedo (such as snow cover), increased upwelling local diffuse radiation yielded an MDAF derived using total radiation (sum of # and " components) ~40% larger than the MDAF derived using only # radiation. The study has demonstrated: (1) the magnitude of potential impact of local conditions—principally and cloud cover, but also changes in surface albedo—on assumed j-values; (2) that whilst annual mean MDAF values are similar at Auchencorth Moss and Manchester, there is no contemporaneous correlation between them at hourly resolution; hence MDAF values derived at one site cannot readily be applied at another site. These data illustrate the need to routinely deploy long-term radiometer measurements alongside compositional measurements to support atmospheric chemistry modelling.
Original languageEnglish
Article number1065
Number of pages15
Issue number7
Publication statusPublished - 5 Jul 2022


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