Modelling studies of HOMs and their contributions to new particle formation and growth: comparison of boreal forest in Finland and a polluted environment in China

Abstract

Abstract. Highly oxygenated multifunctional compounds (HOMs) play a key role in new particle formation (NPF), but their quantitative roles in different environments of the globe have not been well studied yet. Frequent NPF events were observed at two "flagship" stations under different environmental conditions, i.e. a remote boreal forest site (SMEAR II) in Finland and a suburban site (SORPES) in polluted eastern China. The averaged formation rate of 6 nm particles and the growth rate of 6-30 nm particles were 0.3 cm −3 s −1 and 4.5 nm h −1 at SMEAR II compared to 2.3 cm −3 s −1 and 8.7 nm h −1 at SORPES, respectively. To explore the differences of NPF at the two stations, the HOM concentrations and NPF events at two sites were simulated with the MALTE-BOX model, and their roles in NPF and particle growth in the two distinctly different environments are discussed. The model provides an acceptable agreement between the simulated and measured concentrations of sulfuric acid and HOMs at SMEAR II. The sulfuric acid and HOM organonitrate concentrations are significantly higher but other HOM monomers and dimers from monoterpene oxidation are lower at SORPES compared to SMEAR II. The model simulates the NPF events at SMEAR II with a good agreement but underestimates the growth of new particles at SORPES, indicating a dominant role of anthropogenic processes in the polluted environment. HOMs from monoterpene oxidation dominate the growth of ultrafine particles at SMEAR II while sulfuric acid and HOMs from aromatics oxidation play a more important role in particle growth. This study highlights the distinct roles of sulfuric acid and HOMs in NPF and particle growth in different environmental conditions and suggests the need for molecular-scale measurements in improving the understanding of NPF mechanisms in polluted areas like eastern China.

Observations of highly oxidized molecules and particle nucleation in the atmosphere of Beijing

“…The OS c observed in Beijing is also higher than that seen in the boreal forest environment of Hyytiälä, despite extremely low NO x concentrations, likely due to low temperature conditions dominating in those conditions (Schobesberger et al, 2013). These degrees of oxidation relatively similar to those seen in other, cleaner environments are likely due to an interplay between the higher temperatures facilitating rapid hydrogen abstractions (Crounse et al, 2013;Quéléver et al, 2019) and the higher concentrations of NO x , HO q 2 , and other RO q 2 molecules terminating the autoxidation sequence more efficiently (Praske et al, 2018;Rissanen, 2018;Garmash et al, 2019).…”

“…ation are much lower. HOM formation is largely dependent upon VOC concentration, oxidant concentration (which will be lower if solar radiation is lower, especially in the case of OH q , the main oxidant of aromatic species especially), and temperature (as H shifts are highly temperature-dependent) (Quéléver et al, 2019), as well as losses by RO q 2 termination before a molecule can become HOM and losses to condensational sink. The low HOM concentration is likely due to these lower temperatures and weaker solar radiation not facilitating HOM formation.…”

“…Although globally biogenic volatile organic compound (BVOC) concentrations far exceed anthropogenic volatile organic compound (AVOC) concentrations, in the urban environment the anthropogenic fraction is far more significant. Formation of HOMs from aromatic compounds has been demonstrated in laboratory studies and these have been hypothesized to be large drivers of NPF in urban environments (Wang et al, 2017;Molteni et al, 2018;Qi et al, 2018). The formation of HOMs through autoxidation processes begins with the reaction of VOCs with OH q , O 3 , or NO q 3 ; formation of a peroxy radical (RO q 2 ) is followed by rapid O 2 additions and intramolecular hydrogen abstractions (Jokinen et al, 2014;Rissanen et al, 2014;.…”

Aerosol mass yields of selected biogenic volatile organic compounds – a theoretical study with nearly explicit gas-phase chemistry

“…The activation energies vary for autoxidation of different RO 2 from α-pinene ozonolysis between 22 and 29 kcal mol −1 (Rissanen et al, 2015), leading to varying autoxidation rates at different temperatures (Roldin et al, 2019). It should be noted that the temperature dependence in PRAM is the first of its kind but needs further evaluation using recent measurements of HOM formation at different temperatures (e.g., Quéléver et al, 2019).…”

“…These results are in good agreement with observations made by Kristensen et al (2017), who observed an increasing contribution of SVOCs at subzero temperatures of 258.15 K, which decrease the fraction of SOA formed from ELVOCs. Again, it should be noted that the temperature dependence of peroxy radical autoxidation product formation still needs further validation based on recent experiments (e.g., Quéléver et al, 2019).…”