<p>It is well known that the high population density of urban regions leads to significant degradation of the quality of the air because of the emissions of pollutants that are by-products of energy production, transportation, and industry. The composition and chemistry of urban air has been studied for many decades and these studies have led to detailed understanding of the factors controlling, for example, the formation of ozone, peroxyacetyl nitrate and other secondary species. In the last 20 to 30 years, significant progress has been made in reducing emissions of volatile organic compounds (VOCs) and oxides of nitrogen (NO<sub>x</sub>) in urban atmospheres. Substantial reductions in the abundance of secondary compounds, though, have been more elusive.</p><p>Research has continued to reveal more and more details of the complex processes involved in the atmospheric degradation of wide varieties of volatile organic compounds (VOCs) of anthropogenic and biospheric (BVOCs) origins. BVOCs include isoprene, monoterpenes and sesquiterpenes, and oxygenated VOCs (OVOCs, such as small alcohols). Emissions of BVOCs depend on several factors such as plant or tree species, temperature, and photosynthetically active radiation. They consist almost exclusively of unsaturated compounds with chemistry somewhat different from those of typical urban organic compound emissions. Oxidation of VOCs can lead to molecules of low volatility that are prone to uptake into the aerosol phase.</p><p>Recent studies conducted in megacities such as Paris, Mexico City, Los Angeles and those in China have led to significant advances in our understanding of the chemical evolution of urban plumes. However, important scientific questions remain on how mixing of anthropogenic and biogenic air masses modifies the composition of urban plumes and hence their impacts. Indeed, the proximity of cites to areas of strong biogenic emissions is not unusual. Many major cities at mid-latitudes are surrounded by forested areas.</p><p>ACROSS (Atmospheric ChemistRy Of the Suburban foreSt) is an integrative, innovative, multi-scale project awarded under the &#8220;Make Our Planet Great Again&#8221; (MOPGA) framework that seeks to definitively improve understanding of the impacts of mixing urban and biogenic air masses on the oxidation of atmospheric VOCs. The ACROSS working hypothesis is that this leads to changes in the production of oxygenated VOCs whose properties (e.g. vapor pressures) alter their importance in incorporation into SOA and their roles in production of ozone and other secondary species. Changes are also expected in the efficiency of radical recycling affecting the atmospheric oxidative capacity. Particularly important is NO<sub>x</sub> transport to suburban biogenic environments and the resulting modification of key chemical processes.</p><p>A key highlight of ACROSS is an intensive, multi-platform measurement campaign in the summer of 2022. It will use instruments staged on an airborne platform, a tower in the Rambouillet Forest near Paris, and other ground sites. The data collected from this campaign will be analyzed and studied to extract information about tropospheric oxidation chemistry generally, but also changes observed in the situation of mixed urban and biogenic air masses.</p><p>This presentation will summarize plans for the ACROSS campaign.</p>
OH and HO<sub>2</sub> radical chemistry during PROPHET 2008 and CABINEX 2009 – Part 1: Measurements and model comparison
