Characterization of Total OH Reactivity in a Rapeseed Field: Results from the COV3ER Experiment in April 2017

Abstract

Croplands remain poorly studied ecosystems in terms of total hydroxyl radical (OH) reactivity, especially when compared to forests. As part of the COV3ER project, total OH reactivity (ROH), defined as the total loss rate of OH due to its reaction with reactive species in the atmosphere, was characterized in a rapeseed field (Grignon, France) during the blooming season in April 2017. Measurements were performed in a dynamic chamber as well as in ambient air using the Comparative Reactivity Method (CRM). Complementary measurements of organic (including a proton transfer reaction quadrupole ion–time of flight mass spectrometry, PTRQi-ToFMS) and inorganic compounds were also performed in order to calculate the expected OH reactivity and evaluate the missing fraction. Measured ROH varied diurnally in the dynamic chamber (mROHchamber) with maxima around 20 to 30 s−1 at midday and minima during dark hours, following the variability of the enclosed branch VOCsrapeseed, which is light- and temperature-dependent. Oxygenated VOCs were the major compounds emitted by the rapeseed crop. However, in terms of contribution to OH reactivity, isoprene accounted for 40% during the daytime, followed by acetaldehyde (21%) and monoterpenes (18%). The comparison between mROHchamber and calculated ROH (cROHchamber) exhibited little or no difference during dark hours, whereas a maximum difference appeared around midday, highlighting a significant missing fraction (46% on average during daytime) mainly related to biogenic temperature- and/or light-dependent emissions.

Modeling Intra‐ and Interannual Variability of BVOC Emissions From Maize, Oil‐Seed Rape, and Ryegrass

“…Finally, the conversion of BVOC emissions into reactivity has shown that not only the emission strength of individual compounds but also the emission pattern and the individual (or group) reactivity of the compounds need to be considered. This has recently also been postulated for a short-term experiment at an oil-seed rape field in France (Bsaibes et al, 2020). In particular compounds with very high OH-reactivities can determine air chemistry in specific periods.…”

“…In contrast to maize, our findings for oil‐seed rape are rather at the upper range of previous field observations regarding methanol (Acton et al., 2018; Gonzaga Gomez et al., 2019) as well as GLV emissions (König et al., 1995). Notably, considerable net emissions of other oxygenated hydrocarbons such as of acetone, acetaldehyde, and ethanol were found that were only seldom reported before (Bsaibes et al., 2020; Gonzaga Gomez et al., 2019; McEwan & MacFarlane Smith, 1998). Terpenoid emissions in oil‐seed rape were either higher (Bsaibes et al., 2020; Himanen et al., 2009; McEwan & MacFarlane Smith, 1998) or lower (König et al., 1995; Müller et al., 2002) than indicated by our observations, with one investigation that could not find any monoterpene emission at all (Morrison et al., 2016).…”

“…Notably, considerable net emissions of other oxygenated hydrocarbons such as of acetone, acetaldehyde, and ethanol were found that were only seldom reported before (Bsaibes et al., 2020; Gonzaga Gomez et al., 2019; McEwan & MacFarlane Smith, 1998). Terpenoid emissions in oil‐seed rape were either higher (Bsaibes et al., 2020; Himanen et al., 2009; McEwan & MacFarlane Smith, 1998) or lower (König et al., 1995; Müller et al., 2002) than indicated by our observations, with one investigation that could not find any monoterpene emission at all (Morrison et al., 2016). Regarding ryegrass, we present the first comprehensive estimate of the BVOC emission spectrum that has been derived from field measurements.…”

Total OH Reactivity Measurements in a Suburban Site of Shanghai

“…There is a good exponential correlation (R missing OH = 0.0024 × exp(0.255 × T), R = 0.74) between the missing OH reactivity (s −1 ) and temperature (°C) from 7:00–19:00 LT from 21 to 28 August, 2020 (Figure 11a), which is similar to observations in previous studies in which emissions of unmeasured primary biogenic VOCs driven by temperature are potential candidates for the daytime missing OH reactivity. (Bsaibes et al., 2020; Di Carlo et al., 2004). On the other hand, such an exponential correlation ( R = 0.14, Figure 11a) is not quite valid for the entire campaign.…”

Investigation of Anthropogenic Monoterpenes in Canadian Cities

“…Total OH reactivity is a method of characterizing the overall loss of the hydroxyl radical OH, representing the total reaction frequencies of OH with all chemicals. This was calculated to examine the overall change of photochemical reactivity in Canadian atmosphere over time Equation is used to calculate the total OH reactivity ( k ) of all chemical species (X i ) monitored under the NAPS program .…”