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

[摘要] Sesquiterpenes (C₁₅H₂₄) are semi-volatile organic compoundsemitted by vegetation and are of interest in atmospheric research becausethey influence the oxidative capacity of the atmosphere and contribute tothe formation of secondary organic aerosols. However, little is known abouttheir emission pattern and no established parameterisation is available forglobal emission models. The aim of this study is to investigate a CentralEuropean spruce forest and its emission response to meteorological andenvironmental parameters, looking for a parameterisation that incorporatesheat and oxidative stress as the main driving forces of the inducedemissions. Therefore, a healthy ca. 80 yr old Norway spruce (Picea abies)tree was selected and a dynamical vegetation enclosure technique was appliedfrom April to November 2011. The emissions clearly responded to temperaturechanges 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 valuesrevealed a vast amount of variability in temperature dependencies((0.02 ± 0.002) < β < (0.27 ± 0.04)) with nodistinct seasonality.

By separating the complete dataset in 10 different ozone regimes, we foundthat in moderately or less polluted atmospheric conditions the main drivingforce of sesquiterpene emissions is the temperature, but when ambient ozonemixing ratios exceed a critical threshold of (36.6 ± 3.9) ppb_v,the emissions become primarily correlated with ozone. Considering thecomplete dataset, cross correlation analysis resulted in highest correlationwith ambient ozone mixing ratios (CC_O3 = 0.63 ± 0.01;CC_T = 0.47 ± 0.02 at t = 0 h for temperature) with a time shift2–4 h prior to the emissions. An only temperature dependent algorithm wasfound to substantially underestimate the induced emissions (20% of themeasured; R² = 0.31). However, the addition of an ozone dependent termimproved substantially the fitting between measured and modelled emissions(81% of the modelled emissions could be explained by the measurements;R² = 0.63), providing confidence about the reliability of the suggestedparameterisation for the spruce forest site investigated.

[学科分类] 地球化学与岩石