The link between atmospheric radicals and newly formed particles at a spruce forest site in Germany

Abstract

It has been claimed for more than a century that atmospheric new particle formation is primarily influenced by the presence of sulphuric acid. However, the activation process of sulphuric acid related clusters into detectable particles is still an unresolved topic. In this study we focus on the PARADE campaign measurements conducted during August/September 2011 at Mt. Kleiner Feldberg in central Germany. During this campaign a set of radicals, organic and inorganic compounds and oxidants and aerosol properties were measured or calculated. We compared a range of organic and inorganic nucleation theories, evaluating their ability to simulate measured particle formation rates at 3 nm in diameter (<i>J</i>₃) for a variety of different conditions. Nucleation mechanisms involving only sulphuric acid tentatively captured the observed noon-time daily maximum in <i>J</i>₃, but displayed an increasing difference to <i>J</i>₃ measurements during the rest of the diurnal cycle. Including large organic radicals, i.e. organic peroxy radicals (RO₂) deriving from monoterpenes and their oxidation products in the nucleation mechanism improved the correlation between observed and simulated <i>J</i>₃. This supports a recently proposed empirical relationship for new particle formation that has been used in global models. However, the best match between theory and measurements for the site of interest was found for an activation process based on large organic peroxy radicals and stabilized Criegee intermediates (sCI). This novel laboratory derived algorithm simulated the daily pattern and intensity of <i>J</i>₃ observed in the ambient data. In this algorithm organic derived radicals are involved in activation and growth and link the formation rate of smallest aerosol particles with OH during daytime and NO₃ during nighttime. Because of the RO₂s lifetime is controlled by HO₂ and NO we conclude that peroxy radicals and NO seem to play an important role for ambient radical chemistry not only with respect to oxidation capacity but also for the activation process of new particle formation. This is supposed to have significant impact of atmospheric radical species on aerosol chemistry and should to be taken into account when studying the impact of new particles in climate feedback cycles

Criegee intermediates and their impacts on the troposphere

“…The Criegee chemistry used in STOCHEM-CRI is different from that of Vereecken et al 93 Texas conurbation, which are very similar to the study 99 who predicted sCI levels up to ~5 × 10 4 cm -3 in Hyytiälä, Finland, and Hohenpeissenberg, Germany. Bonn et al 110 found sCI levels in the range of 2 × 10 4 cm -3 to 4 × 10 5 42,105 Detection of sCI in the atmosphere may soon become possible by direct measurement techniques such as near-UV cavity ringdown spectroscopy, 21 UV-Vis spectroscopy, 58,64 IR spectroscopy, 112 Proton transfer reaction time of flight mass spectrometry (PTR-TOF-MS), [113][114] or chemical ionisation mass spectrometry (CIMS). 70,115 However, it should be noted that direct measurements will represent a significant analytical challenge as a result of the low concentration of sCIs that are predicted in the atmosphere.…”

From emissions to ambient mixing ratios: online seasonal field measurements of volatile organic compounds over a Norway spruce-dominated forest in central Germany

“…The dominant spruce trees reach a maximum height of about 17 m, but the lowest living branches can also be found at 2 m height at the edge of the forest, where measurements took place. Further information on the forest characteristics can be found in Crowley et al (2010) and Bonn et al (2013 …”

What effect does VOC sampling time have on derived OH reactivity?

“…Measurements were taken between August and September 2011 at the Taunus observatory on the summit of Kleiner Feldberg (50°13´25" N, 8°26´56" E) under various meteorological conditions. A detailed description of the measurement site and measurements performed during PARADE can be found in Crowley et al (2010) and Bonn et al (2014).…”