Analysis of emissions-driven changes in the oxidation capacity of the atmosphere in Europe

• Published in: The Science of the total environment 2022-06, Vol.827, p.154126-154126, Article 154126
• Main Authors: Jung, Daeun, de la Paz, David, Notario, Alberto, Borge, Rafael
• Format: Article
• Language: English
• Subjects: Air quality modelling; CMAQ; Oxidation capacity; Radicals; Tropospheric oxidants
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.154126

Anthropogenic emissions in Europe have been gradually reduced thanks to a combination of factors, including restrictive regulation and policy implementation, fuel switching, technological developments, and improved energy efficiencies. Many measures have been specifically introduced to meet the annual and hourly limit value of NO2 for the protection of human health, mainly targeting traffic emissions. Due to NOX reduction policies in Europe, NO2 levels have generally declined, but O3 concentrations have been found to increase. This phenomenon would cause changes in the oxidant capacity of the atmosphere, altering the concentration of tropospheric oxidants in urban areas. The Community Multiscale Air Quality (CMAQ) modelling system has been used to study concentration changes of NO2, O3 and the main radicals in Europe between 2007 and 2015 for two months representatives of winter and summer conditions (January and July). In addition to describing the general situation in Europe, variations in pollutants along with NOX emission changes over 67 large European cities have been analysed by means of statistical methods. NOX emissions and NO2 concentrations decreased in both seasons during the period in all the selected cities. In most of them O3 concentrations increased in winter but decreased in summer. The concentration of the OH radical, the main oxidant during the daytime, shows an increase in winter. This is also the case for the main cities in summer although we found a general decrease in continent for this season. The NO3 radical, the main night-time oxidant, was found to increase in winter and decrease in summer. HNO3 shows a concentration decline in both seasons. The studied cities are classified in five groups by means of k-mean clustering procedure. We identified five groups with specific patterns, suggesting that the oxidant capacity of the European urban atmospheres has reacted differently to NOX emission abatement policies. [Display omitted] •Levels of tropospheric oxidants simulated by the CMAQ modelling system over Europe•NO2 ambient concentration reduced by 24% due to NOx 2007–2015 emission abatements•Contrasting O3 trends: general increase in winter and decrease in summer•Generalized significant reductions (over 30%) of HNO3 in both seasons•Differences across large European cities in seasonal trends of OH and NO3 radicals