The COVID-19 pandemic forced governments around the world to impose restrictions on daily life to prevent the spread of the virus. This resulted in unprecedented reductions in anthropogenic activity, and reduced emissions of certain air pollutants, namely oxides of nitrogen. The UK ‘lockdown’ was enforced on 23/03/2020, which led to restrictions on movement, social interaction, and ‘non-essential’ businesses and services. This study employed an ensemble of measurement and modelling techniques to investigate changes in air quality, atmospheric composition and boundary layer reactivity in the South East of the UK post-lockdown. The techniques employed included in-situ gas- and particle-phase monitoring within central and local authority air quality monitoring networks, remote sensing by long path Differential Optical Absorption Spectroscopy and Sentinel-5P's TROPOMI, and detailed 0-D chemical box modelling. Findings showed that de-trended NO 2 concentrations decreased by an average of 14–38% when compared to the mean of the same period over the preceding 5-years. We found that de-trended particulate matter concentrations had been influenced by interregional pollution episodes, and de-trended ozone concentrations had increased across most sites, by up to 15%, such that total O x levels were roughly preserved. 0-D chemical box model simulations showed the observed increases in ozone concentrations during lockdown under the hydrocarbon-limited ozone production regime, where total NO x decreased proportionally greater than total non-methane hydrocarbons, which led to an increase in total hydroxyl, peroxy and organic peroxy radicals. These findings suggest a more complex scenario in terms of changes in air quality owing to the COVID-19 lockdown than originally reported and provide a window into the future to illustrate potential outcomes of policy interventions seeking large-scale NO x emissions reductions without due consideration of other reactive trace species.

Background: Long Covid, characterised by symptoms after Covid-19 infection which persist for longer than 12 weeks, is becoming an important societal and economic problem. As Long Covid was novel in 2020, there has been debate regarding its aetiology and whether it is one, or multiple, syndromes. This study assessed risk factors associated with Long Covid and examined symptom clusters that might indicate sub-types. Methods: 4,040 participants reporting for >4 months in the Covid Symptom Study App were included. Multivariate logistic regression was undertaken to identify risk factors associated with Long Covid. Cluster analysis (K-modes and hierarchical agglomerative clustering) and factor analysis were undertaken to investigate symptom clusters. Results: Long Covid affected 13.6% of participants. Significant risk factors included being female (P < 0.01), pre-existing poor health (P < 0.01), and worse symptoms in the initial illness. A model incorporating sociodemographics, comorbidities, and health status predicted Long Covid with an accuracy (AUROC) of 76%. The three clustering approaches gave rise to different sets of clusters with no consistent pattern across methods. Conclusions: Our model of risk factors may help clinicians predict patients at higher risk of Long Covid, so these patients can rest more, receive treatments, or enter clinical trials; reducing the burden of this long-term and debilitating condition. No consistent subtypes were identified.

&lt;p&gt;COVID-19 required governments across the globe put into place a range of measures which resulted in many industries suspending operations and most citizens (i.e., non &amp;#8216;key-workers&amp;#8217;) staying in their homes. As such, anthropogenic activity around the globe decreased rapidly, to such an extent that emissions of air pollutants began to decline dramatically, with this period now being referred to as an &amp;#8216;anthropause&amp;#8217;. In the early stages of the pandemic, remote sensing data from satellites indicated that nitrogen dioxide (NO&amp;#8322;) concentrations had fallen by as much as 30% across China and by as much as 50% across areas of central Europe. Early work using in-situ measurements confirmed these findings, with studies from China, Korea, India, the USA and Europe all reporting decreases in ambient NOx concentrations. The UK government advised that the general population should avoid &amp;#8216;non-essential&amp;#8217; travel and social contact, on 16th March 2020. &amp;#160;Subsequently, on 23rd March 2020, the government announced a UK-wide partial &amp;#8216;lockdown&amp;#8217;, to contain the spread of the virus.&amp;#160;&lt;/p&gt;&lt;p&gt;In this work, we combine findings from the University of Brighton&amp;#8217;s Brighton Atmospheric Observatory and the ESA's Sentinel-5P satellite, to investigate changes in tropospheric Nitrogen Dioxide concentrations in the South East of the UK during the COVID-19 pandemic. BAO comprises a climate controlled, clean laboratory and analytical instruments for making detailed, real-time measurements of tropospheric composition, and is situated in a suburban background environment, roughly 5 km from Brighton city centre.&amp;#160;&lt;/p&gt;&lt;p&gt;Maps showing regional daily average NO&amp;#8322; concentrations as recorded by TROPOMI were created over (a) the period 25/03/2019&amp;#8211;22/04/2019 (i.e. the pre-pandemic baseline) and (b) 23/03/2020&amp;#8211;20/04/2020 (i.e. post-implementation of lockdown restrictions). TROPOMI measurements were compared to measurements made on the ground using a long-path DOAS (total path length 300m) for the same time periods. The data confirms findings from analysis of in-situ monitor observations made by the Sussex-Air Network and DEFRA Automatic Urban and Rural Network (AURN), extending the reach of the data capture to the entire South East of the UK on a 7 &amp;#215; 7 km resolution scale. In-line with the in-situ monitors, TROPOMI measured a decrease in the concentrations of NO2 across the entire region during the lockdown, with the regional average value falling by 33%, from 4.9 &amp;#215; 10^16 to 3.3 &amp;#215; 10^16 molec m^-2. The largest changes in NO2 were observed in the centre of the region, in the areas surrounding London and at certain coastal locations. &amp;#160;&lt;/p&gt;&lt;p&gt;TROPOMI measured NO2 values across Brighton and Hove during the 2020 lockdown period to be 59% of those measured over roughly the same time period the previous year (with mean values falling from 4.4 &amp;#215; 10^16 to 2.9 &amp;#215; 10^16 molecule m^-2), comparing favourably with DOAS, which recorded NO&amp;#8322; values that were ~64% of those measured during the previous two years over roughly the same time period. &amp;#160;&lt;/p&gt;&lt;p&gt;The methodology is also extended to London, Birmingham and Manchester, the 1st, 2nd and 6th largest cities within the UK.&amp;#160;&lt;/p&gt;