Ozone stress as a driving force of sesquiterpene emissions: a suggested parameterisation

Abstract

Abstract. Sesquiterpenes (C 15 H 24 ) are semi-volatile organic compounds emitted by vegetation and are of interest in atmospheric research because they influence the oxidative capacity of the atmosphere and contribute to the formation of secondary organic aerosols. However, little is known about their emission pattern and no established parameterisation is available for global emission models. The aim of this study is to investigate a Central European spruce forest and its emission response to meteorological and environmental parameters, looking for a parameterisation that incorporates heat and oxidative stress as the main driving forces of the induced emissions. Therefore, a healthy ca. 80 yr old Norway spruce (Picea abies) tree was selected and a dynamical vegetation enclosure technique was applied from April to November 2011. The emissions clearly responded to temperature changes with small variations in the β-factor along the year (β spring = 0.09 ± 0.01, β summer = 0.12± 0.02, β autumn = 0.11 ± 0.02). However, daily calculated values revealed a vast amount of variability in temperature dependencies ((0.02 ± 0.002) < β < (0.27 ± 0.04)) with no distinct seasonality.By separating the complete dataset in 10 different ozone regimes, we found that in moderately or less polluted atmospheric conditions the main driving force of sesquiterpene emissions is the temperature, but when ambient ozone mixing ratios exceed a critical threshold of (36.6 ± 3.9) ppb v , the emissions become primarily correlated with ozone. Considering the complete dataset, cross correlation analysis resulted in highest correlation with ambient ozone mixing ratios (CC O 3 = 0.63 ± 0.01; CC T = 0.47 ± 0.02 at t = 0 h for temperature) with a time shift 2-4 h prior to the emissions. An only temperature dependent algorithm was found to substantially underestimate the induced emissions (20 % of the measured; R 2 = 0.31). However, the addition of an ozone dependent term improved substantially the fitting between measured and modelled emissions (81 % of the modelled emissions could be explained by the measurements; R 2 = 0.63), providing confidence about the reliability of the suggested parameterisation for the spruce forest site investigated.

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

“…It is generally believed that isoprenoids can protect the plant against oxidative stress during photosynthesis (Loreto at al., 2001Vickers et al, 2009;Jardine et al, 2012). Within this context, in previously reported work, Norway spruce has been found to regulate its sesquiterpene emission rates according to ambient ozone concentrations (Bourtsoukidis et al 2012), and Karlsson et al (2006) provided statistical evidence of the negative effect of ozone on the stem diameter of mature trees. There is also some evidence to suggest that ozone causes even more damage to vegetation than drought-induced limitation of photosynthesis (Karnosky et al, 2003;Matyssek et al, 2006).…”

“…General information about the analytical technique can be found in the literature (Lindinger et al, 1998;Blacke et al, 2009, and references therein), while more specific information about the settings of this study can be found in Bourtsoukidis et al (2012). Briefly, the PTR-MS was operated under standard conditions with a drift tube voltage of 600 V and drift tube pressure of 2.3 mbar.…”

“…The loss due to reactions with ambient ozone is not important for the oxygenated species but it does affect the highly reactive SQT emission rates, as discussed in Bourtsoukidis et al (2012). Hereafter, biogenic emissions were quantified in ng g(dw) −1 h −1 .…”

“…80 years old) Norway spruce tree from 8 April to 11 November 2011, as described in Bourtsoukidis et al (2012). Briefly, the 15 L cylindrical-shaped glass cuvette remained open for most of the time in order to keep the environmental parameters close to ambient levels and minimize stress to the plant (Ortega and Helmig, 2008).…”

“…Stronger differences were observed in a similar intercomparison with photosynthetic active radiation (PAR) during September. Two PAR sensors (LI-190SZ, LI-190SL; Li-Cor Inc., Lincoln, NB, USA) were placed inside and outside of the chamber and revealed differences from 25 to 45 %, depending on the solar zenith angle (Bourtsoukidis et al, 2012). For the duration of the closing period, during the complete measuring period, the temperature rose on average by 0.91 ± 0.82 • C, while relative humidity and ozone dropped by 3.5 ± 3.5 % and 2.9 ± 2.5 ppbv respectively.…”