Reactive uptake of NO2 on volcanic particles: A possible source of HONO in the atmosphere

The heterogeneous degradation of nitrogen dioxide(NO2) on five samples of natural Icelandic volcanic particles has been investigated.Laboratory experiments were carried out under simulated atmospheric conditions using a coated wall flow tube(CWFT).The CWFT reactor was coupled to a blue light nitrogen oxides analyzer(NOx analyzer),and a long path absorption photometer(LOPAP) to monitor in real time the concentrations of NO2,NO and HONO,respectively.Under dark and ambient relative humidity conditions,the steady state uptake coefficients of NO2 varied significantly between the volcanic samples probably due to differences in magma composition and morphological variation related with the density of surface OH groups.The irradiation of the surface with simulated sunlight enhanced the uptake coefficients by a factor of three indicating that photo-induced processes on the surface of the dust occur.Furthermore,the product yields of NO and HONO were determined under both dark and simulated sunlight conditions.The relative humidity was found to influence the distribution of gaseous products,promoting the formation of gaseous HONO.A detailed reaction mechanism is proposed that supports our experimental observations.Regarding the atmospheric implications,our results suggest that the NO2 degradation on volcanic particles and the corresponding formation of HONO is expected to be significant during volcanic dust storms or after a volcanic eruption.

Development and validation of a thermally regulated atmospheric simulation chamber(THALAMOS): A versatile tool to simulate atmospheric processes

Atmospheric simulation chambers,are unique tools for investigating atmospheric processes in the gas and heterogeneous phases.They can provide a controlled yet realistic environment that simulates atmospheric conditions.In the current study,a Teflon atmospheric simulation chamber of 600 L,named THALAMOS(thermally regulated atmospheric simulation chamber) has been developed and cross-validated.THALAMOS can be operated over the temperature range 233 to 373 K under both static and flow conditions.It is equipped with state of the art instrumentation(selective ion flow tube mass spectrometry(SIFT-MS),long path Fourier transform infrared spectroscopy(FTIR),gas chromatography-mass spectrometry(GC-MS),various analyzers) for the in-line monitoring of both reactants and products.THALAMOS was validated by measuring the rate coefficients of well documented reactions,i.e.the reaction of ethanol with OH radicals and the reaction of dichloromethane with Cl atoms,in a wide temperature range.Two different detection techniques were used in parallel,FTIR and SIFT-MS,to internally cross-validate the obtained results.The measured rate coefficients are in excellent agreement,both between each other and with the literature recommended values.Furthermore,the gas phase oxidation of toluene by Cl atoms(kinetics and product yields) was studied in the temperature range of 253 to 333 K.To the best of our knowledge,THALAMOS is a unique facility on national level and among a few smog chambers internationally that can be operated in such a wide temperature range providing the scientific community with a versatile tool to simulate both outdoor and indoor physicochemical processes.