Atmospheric satellite-based and in situ surface observations on summertime trace gases (CO, CO2, CH4) over the metropolitan area of Bucharest
Authors: Corbu Marius-Paul , Calcan Andreea , Vizireanu Ioana , Moaca Denisa Elena , Chiritescu Robert-Valentin , Roeckmann Thomas , Maazallahi Hossein , Fernandez Julianne Mae , France James , Iorga Gabriela 
Published: March 2020

&lt;p&gt;Although anthropogenic emissions of trace gases have decreased over the last decades in Europe, strong additional reductions are required to reach the goals of the Paris climate agreements. In addition, air pollution is an issue of great concern for the inhabitants of the metropolitan area of Bucharest, as the local air quality is often poor. The rapid development of the city, increased traffic volume from a mixed vehicle fleet (different technologies and fuels), and other factors are strong contributors of emissions of greenhouse gases and air pollutants in Bucharest.&lt;/p&gt;&lt;p&gt;The goal of this research was the assessment of CO, CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; concentrations in Bucharest, identification of potential emissions hotspots and their causes (anthropogenic or natural/biogenic, local or distant) and determination of the background values.&lt;/p&gt;&lt;p&gt;Measurements were performed in summer 2019 in four districts of Bucharest covering about two thirds of the metropolitan area during the Romanian Methane Emissions from Oil&amp;gas (ROMEO) campaign with high resolution (1 sec). These data sets were complemented with satellite observations of CO and CH&lt;sub&gt;4&lt;/sub&gt; from Copernicus Sentinel-5P at a resolution of 7 km&lt;sup&gt;2&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;Hourly meteorological data, temperature, relative humidity, wind speed and direction, and atmospheric pressure were added to the air pollutant data set because synoptic conditions can strongly influence the levels of pollution. Air mass origins were investigated by computing backward air mass trajectories using the HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) model for 72 hours back.&lt;/p&gt;&lt;p&gt;Points of high concentrations of CO, CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; near the surface were identified which are, most likely, linked to local anthropogenic activities in the nearby surroundings. We identified a variation of concentrations of CO from 0.01 to 101 ppm, of CO&lt;sub&gt;2&lt;/sub&gt; from 388 to 6556 ppm, and of CH&lt;sub&gt;4&lt;/sub&gt; from 1.89 to 246 ppm, while background levels are as follows: 0.071&amp;#177;0.042 ppm CO, 392.68&amp;#177;3.01 ppm CO&lt;sub&gt;2&lt;/sub&gt;, and 1.93&amp;#177;0.016 ppm CH&lt;sub&gt;4&lt;/sub&gt;.&lt;/p&gt;&lt;p&gt;Results of our study provide an up to date quantitative image of CO, CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; hotspots in the Bucharest area, which is important for modeling air quality and may also help to improve the relationships between column integrated air pollution data with in situ ground observations.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Acknowledgement:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;This research is supported by ROMEO project, developed under UNEP&amp;#8217;s financial support PCA/CCAC/UU/DTIE19-EN652. Partial financial support from UB198/Int project is also acknowledged.&lt;/p&gt;&lt;p&gt;The authors acknowledge the free use of tropospheric CO and CH&lt;sub&gt;4&lt;/sub&gt; column data from TROPOMI (Sentinel-5P) sensor from https://s5phub.copernicus.eu and the NOAA Air Resources Laboratory for the provision of the HYSPLIT transport model available at READY website https://www.ready.noaa.gov&lt;/p&gt;&lt;p&gt;Special thanks to all INCAS technical staff for their support in performing the campaigns.&lt;/p&gt;