Simple proxies for estimating the concentrations of monoterpenes and their oxidation products at a boreal forest site

Abstract

Abstract. The oxidation products of monoterpenes likely have a crucial role in the formation and growth of aerosol particles in boreal forests. However, the continuous measurements of monoterpene concentrations are usually not available on decadal timescales, and the direct measurements of the concentrations of monoterpene oxidation product have so far been scarce. In this study we developed proxies for the concentrations of monoterpenes and their oxidation products at a boreal forest site in Hyytiälä, southern Finland. For deriving the proxies we used the monoterpene concentration measured with a proton transfer reaction mass spectrometer (PTR-MS) during 2006-2013. Our proxies for the monoterpene concentration take into account the temperature-controlled emissions from the forest ecosystem, the dilution caused by the mixing within the boundary layer and different oxidation processes. All the versions of our proxies captured the seasonal variation of the monoterpene concentration, the typical proxy-to-measurements ratios being between 0.8 and 1.3 in summer and between 0.6 and 2.6 in winter. In addition, the proxies were able to describe the diurnal variation of the monoterpene concentration rather well, especially in summer months. By utilizing one of the proxies, we calculated the concentration of oxidation products of monoterpenes by considering their production in the oxidation and their loss due to condensation on aerosol particles. The concentration of oxidation products was found to have a clear seasonal cycle, with a maximum in summer and a minimum in winter. The concentration of oxidation products was lowest in the morning or around noon and highest in the evening. In the future, our proxies for the monoterpene concentration and their oxidation products can be used, for example, in the analysis of new particle formation and growth in boreal environments.

Long-term analysis of clear-sky new particle formation events and nonevents in Hyytiälä

“…The largest difference in [OxOrg] between the NPF events and nonevents, in terms of its median value, was recorded for January and the least difference was recorded for May. It is to be noted that the proxy values represent the measured values less accurately during winter than during the other periods (Kontkanen et al, 2016b).…”

“…The scaling was made in order to fit the current data. The median value of [OxOrg] during the event days in April and May was found to be 1.6 × 10 7 cm −3 , whereas the revised median value of [OxOrg] by Kontkanen et al (2016b) is 1.3 × 10 8 cm −3 . The scaling factor is the ratio between new and original [OxOrg] (0.1194).…”

“…The coefficient k (m 2 W −1 s −1 ) is obtained from the comparison of the proxy concentration to the available measured H 2 SO 4 data and has a median value of 9.9 × 10 −7 m 2 W −1 s −1 . The concentration of monoterpene oxidation products, called oxidized organic compounds (OxOrg) here, is estimated using a proxy developed by Kontkanen et al (2016b). This proxy is calculated by using the concentrations of different oxidants (the measured ozone concentration [O 3 ] and parameterizations for the hydroxyl and nitrate radical concentration, [OH] and [NO 3 ], respectively) and their reaction rates, k i , with the monoterpenes.…”

“…This proxy is calculated by using the concentrations of different oxidants (the measured ozone concentration [O 3 ] and parameterizations for the hydroxyl and nitrate radical concentration, [OH] and [NO 3 ], respectively) and their reaction rates, k i , with the monoterpenes. The MT proxy (in this case MT proxy1,doy ) is calculated by taking into account the effect of temperature-driven emissions, the mixing of the boundary layer and the oxidation of monoterpenes (Kontkanen et al, 2016b).…”

Sesquiterpenes identified as key species for atmospheric chemistry in boreal forest by terpenoid and OVOC measurements

“…Proton transfer reaction mass spectrometers (PTR-MSs) are often used for measurements of fluxes or concentrations of MTs (Yuan et al 2017) and there are already long data sets on ambient air concentrations of MTs measured by PTR-MSs even in boreal forest (Lappalainen et al 2009, Kontkanen et al 2016. PTR-MS measurements of SQT concentrations are not common, 25 but there are some data available from the tropical forests (Kim et al 2009, Jardine et al 2011).…”