Local and regional enhancements of GHGs in Thessaloniki, inferred from ground-based FTIR measurements

Global warming and subsequent climate change are currently a major issue both in the scientific community and the society. Therefore it is highly important to consistently monitor the concentrations of greenhouse gases that affect the incoming-outgoing energy balance. To that end, a portable Bruker EM27/SUN FTIR spectrometer is operated in Thessaloniki, Greece since January 2019, performing measurements of total column-averaged dry air mole fractions of trace gases, denoted as X-gases. In this study, we demonstrate the utility of available measurements of greenhouse gases (GHGs) to identify the origin of enhanced concentrations. Copernicus Atmosphere Monitoring Service (CAMS) reanalysis data are used synergetically with FTIR measurements. XCO₂ shows an obvious annual increase (over 2.2 ppm per year) and a clear seasonal variation with high increased concentrations during cold season and decreased concentration during summer period due to photosynthesis activity. XCH₄ shows an annual increase and a positive trend. The continuous fire episodes in Athens and North Evia during July and August 2021 led to an unprecedented increase in the concentrations of CO of over 130 %, compared to the typical averaged mean values during August in Thessaloniki. In this paper we investigate the seasonal dependency between CO-CO₂ and CO-CH₄ enhancements with respect to the prevailing wind direction and we examine if meteorological parameters, such as wind direction and speed, could reveal the origin of enhanced X-gas variations. We applied two different approaching methods to detect long-term and short-term signals of the trace gases. In general, concerning the FTIR measurements, during summer and autumn XCO₂, XCO and XCH₄ enhancements are observed for low and medium speed winds. Winds mainly originating from SW directions have transported large amounts of CO₂, CO and CH₄ from the big fires near Athens and N. Evia in summer 2021 to Thessaloniki. The fire emissions generate higher variability of the columns of target gases (over 0.022 ppm in the S and SW wind direction).