Gunnar W. Schade

Fluxes of oxygenated volatile organic compounds from a ponderosa pine plantation

We present the first canopy-scale, continuous, long-term flux measurements of a suite of oxygenated volatile organic compounds (OVOCs). Fluxes were measured above a ponderosa pine plantation, adjacent to the Blodgett Forest Research Station (38°53′42.9″N, 120°37′57.9″W, 1315 m elevation), with a fully automated relaxed eddy accumulation (REA) system coupled to a dual GC-FID system. Quantified OVOCs included 2-methyl-3-buten-2-ol (MBO), methanol, ethanol, acetaldehyde, and acetone. These compounds were the most abundant nonmethane VOCs at this site and were highly correlated with each other, especially during daytime. Fluxes were dominated by MBO and methanol with daytime average emissions of ∼1.3 mg C m−2 h−1. Ethanol, acetaldehyde, and acetone fluxes were approximately a factor of 5 lower. All fluxes showed diurnal cycles with maxima around noon and minima at night. Temperature and light were the main drivers for MBO emission, and the canopy level flux responses were virtually identical with previously measured leaf level fluxes from ponderosa pine trees at the same site. Ambient temperature appeared to be the most important driver of the other OVOC fluxes, but moisture also played a role, particularly for ethanol and acetone emissions, shown for the first time under field conditions. Soil and litter emissions, measured using a Pyrex glass chamber, contributed significantly to the canopy level fluxes of methanol, acetaldehyde, and acetone, and had a much smaller contribution to the canopy fluxes of ethanol. If the magnitude of these OVOC fluxes is similar in other ecosystems, they will have to be considered a major volatile organic compound emission to the atmosphere and a potentially significant carbon loss from the biosphere.

Are monoterpene emissions influenced by humidity

Monoterpene mixing ratios and fluxes were measured above a ponderosa pine plantation in the Sierra Nevada mountains from July to October 1998. Data were obtained during a variety of weather regimes including periods of extreme heat and dryness as well as during rain. Monoterpene emissions were highly elevated during and after the rain events, and the expected exponential increase of emissions with temperature did not occur during extremely hot and dry conditions, suggesting an influence of ambient humidity levels on monoterpene emissions. Therefore, we propose a modified emission algorithm based on responses to both temperature and humidity.

Observational constraints on the contribution of isoprene oxidation to ozone production on the western slope of the Sierra Nevada, California

[1] Observations of isoprene and its oxidation products methacrolein (MACR) and methyl vinyl ketone (MVK) are used to quantify the impact of isoprene oxidation on ozone production along the western slope of the Sierra Nevada mountains. Regular daytime up-slope wind flow patterns transport anthropogenic volatile organic compounds (VOC) and NOx emissions from the Central Valley toward the Sierra Nevada. A north– south band of oak forests stretching along the foothills and located approximately halfway between Sacramento and our measurement site (Blodgett Forest Research Station; elevation 1315 m) injects isoprene into this mixture. Subsequently, high ozone levels are encountered in these air masses. At Blodgett, daytime mixing ratios of isoprene’s oxidation products and ozone were highly correlated. The observed daytime MVK/MACR ratio was used to estimate a mean [OH] of 9 (±4) � 10 6 molec. cm � 3 between the measurement site and the Sierra foothills. The slope of the correlation between ozone and MVK was analyzed and compared to theoretical yield ratios for the photooxidation of isoprene to estimate the fraction of total ozone production due to isoprene oxidation. On average, over 40% of the observed midday ozone formation in this region was attributable to isoprene oxidation. On ozone episode days (maximum [O3] > 90 ppb), the mean isoprene contribution was over 70%. The calculated isoprene contribution to ozone production was variable from day to day but tended to increase exponentially with both isoprene input and air temperature. NOx conditions in the up-slope air masses were very important in determining the ozone formation potential of isoprene, and the general dominance of isoprene as an ozone precursor suggests that summertime ozone abatement strategies for the region must focus on anthropogenic NOx rather than VOC reductions. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry

Observational insights into aerosol formation from isoprene.

Atmospheric photooxidation of isoprene is an important source of secondary organic aerosol (SOA) and there is increasing evidence that anthropogenic oxidant emissions can enhance this SOA formation. In this work, we use ambient observations of organosulfates formed from isoprene epoxydiols (IEPOX) and methacrylic acid epoxide (MAE) and a broad suite of chemical measurements to investigate the relative importance of nitrogen oxide (NO/NO2) and hydroperoxyl (HO2) SOA formation pathways from isoprene at a forested site in California. In contrast to IEPOX, the calculated production rate of MAE was observed to be independent of temperature. This is the result of the very fast thermolysis of MPAN at high temperatures that affects the distribution of the MPAN reservoir (MPAN / MPA radical) reducing the fraction that can react with OH to form MAE and subsequently SOA (F(MAE formation)). The strong temperature dependence of F(MAE formation) helps to explain our observations of similar concentrations of IEPOX-derived organosulfates (IEPOX-OS; ~1 ng m(-3)) and MAE-derived organosulfates (MAE-OS; ~1 ng m(-3)) under cooler conditions (lower isoprene concentrations) and much higher IEPOX-OS (~20 ng m(-3)) relative to MAE-OS (<0.0005 ng m(-3)) at higher temperatures (higher isoprene concentrations). A kinetic model of IEPOX and MAE loss showed that MAE forms 10-100 times more ring-opening products than IEPOX and that both are strongly dependent on aerosol water content when aerosol pH is constant. However, the higher fraction of MAE ring opening products does not compensate for the lower MAE production under warmer conditions (higher isoprene concentrations) resulting in lower formation of MAE-derived products relative to IEPOX at the surface. In regions of high NOx, high isoprene emissions and strong vertical mixing the slower MPAN thermolysis rate aloft could increase the fraction of MPAN that forms MAE resulting in a vertically varying isoprene SOA source.

Organosulfates as Tracers for Secondary Organic Aerosol (SOA) Formation from 2-Methyl-3-Buten-2-ol (MBO) in the Atmosphere

2-Methyl-3-buten-2-ol (MBO) is an important biogenic volatile organic compound (BVOC) emitted by pine trees and a potential precursor of atmospheric secondary organic aerosol (SOA) in forested regions. In the present study, hydroxyl radical (OH)-initiated oxidation of MBO was examined in smog chambers under varied initial nitric oxide (NO) and aerosol acidity levels. Results indicate measurable SOA from MBO under low-NO conditions. Moreover, increasing aerosol acidity was found to enhance MBO SOA. Chemical characterization of laboratory-generated MBO SOA reveals that an organosulfate species (C5H12O6S, MW 200) formed and was substantially enhanced with elevated aerosol acidity. Ambient fine aerosol (PM2.5) samples collected from the BEARPEX campaign during 2007 and 2009, as well as from the BEACHON-RoMBAS campaign during 2011, were also analyzed. The MBO-derived organosulfate characterized from laboratory-generated aerosol was observed in PM2.5 collected from these campaigns, demonstrating that it is a molecular tracer for MBO-initiated SOA in the atmosphere. Furthermore, mass concentrations of the MBO-derived organosulfate are well correlated with MBO mixing ratio, temperature, and acidity in the field campaigns. Importantly, this compound accounted for an average of 0.25% and as high as 1% of the total organic aerosol mass during BEARPEX 2009. An epoxide intermediate generated under low-NO conditions is tentatively proposed to produce MBO SOA.

Plant physiological influences on the fluxes of oxygenated volatile organic compounds from ponderosa pine trees

elevation), with a fully automated relaxed eddy accumulation system coupled to a dual gas chromatograph-flame ionization detector (GC-FID) system. These measurements were initially reported by Schade and Goldstein [2001]. Here we further analyze these data to explore the physiological controls on emissions of 2-methyl-3-buten-2-ol (MBO), ethanol, and acetaldehyde. Measured MBO fluxes were compared to fluxes predicted by a detailed leaf-level emission model. Although the match was very good in general, the model failed to predict a declined emission potential on cooler days following a very cold night. It also consistently overpredicted fluxes in the morning, while underpredicting fluxes in the afternoon, particularly on warm days. We conclude that the ponderosa pine MBO emission potential changes in response to recent environmental temperatures on diurnal and daily timescales, similar to changes reported for isoprene emissions. Though ambient temperature appeared to be the most important driver of ethanol and acetaldehyde fluxes, vapor pressure deficit strongly influenced ethanol emissions from ponderosa pine, suggesting that stomatal opening impacts emissions. Ethanol emissions were also found to increase after high ozone deposition fluxes, which supports the theory that ozone-induced stress may trigger fermentation processes in the leaves. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0365 Atmospheric Composition and Structure: Troposphere— composition and chemistry; KEYWORDS: VOC emissions, methylbutenol, ethanol, ponderosa pine, physiology

Real-time monitoring of emissions from monoethanolamine-based industrial scale carbon capture facilities.

We demonstrate the capabilities and properties of using Proton Transfer Reaction time-of-flight mass spectrometry (PTR-ToF-MS) to real-time monitor gaseous emissions from industrial scale amine-based carbon capture processes. The benchmark monoethanolamine (MEA) was used as an example of amines needing to be monitored from carbon capture facilities, and to describe how the measurements may be influenced by potentially interfering species in CO2 absorber stack discharges. On the basis of known or expected emission compositions, we investigated the PTR-ToF-MS MEA response as a function of sample flow humidity, ammonia, and CO2 abundances, and show that all can exhibit interferences, thus making accurate amine measurements difficult. This warrants a proper sample pretreatment, and we show an example using a dilution with bottled zero air of 1:20 to 1:10 to monitor stack gas concentrations at the CO2 Technology Center Mongstad (TCM), Norway. Observed emissions included many expected chemical species, dominantly ammonia and acetaldehyde, but also two new species previously not reported but emitted in significant quantities. With respect to concerns regarding amine emissions, we show that accurate amine quantifications in the presence of water vapor, ammonia, and CO2 become feasible after proper sample dilution, thus making PTR-ToF-MS a viable technique to monitor future carbon capture facility emissions, without conventional laborious sample pretreatment.

VOC Concentrations in an Indoor Workplace Environment of a University Building

An indoor air quality survey was conducted at selected indoor environments in the Department of Physics and Electrical Engineering of the University of Bremen, Germany, during August 2005. The mean indoor/ outdoor (I/O) ratios of pollutants appeared to be higher than 1.0 for most volatile organic compounds (VOCs). Apart from direct emissions from indoor materials and infiltration of outdoor air, environmental tobacco smoke (ETS) was a dominant factor in indoor pollution. Pollutants which were commonly associated with cleaning products and materials, including monoterpenes, aldehydes and acetone exhibited general trends of higher concentrations indoors compared to outdoor levels. Indoor concentrations of many VOCs were found to be 2—10 times higher during weekdays as compared to the weekend, exhibiting a strong correlation with human activities. A comparison with previous studies on the health risks due to selected VOCs indicates that long-term exposure to the peak values reported in this study has potential to develop adverse health effects to the occupants whereby reducing the efficiency in the workplace.

Methanol and acetaldehyde fluxes over ryegrass

Oxygenated volatile organic compounds (OVOCs) play an active role in tropospheric chemistry but our knowledge concerning their release and ultimate fate is limited. However, the recent introduction of Proton Transfer Reaction Mass Spectrometry (PTRMS) has improved our capability to make direct field observations of OVOC mixing ratios and fluxes. We used PTRMS in an eddy covariance setup to measure selected OVOC exchange rates above a well-characterized agricultural plot in Northern Germany. In fall 2003, mixing ratios of methanol and acetaldehyde 2m above the field ranged from 1 to 10 and 0.4 to 2.1 ppb, respectively, well correlated with one another. Fluxes of both gases were followed for growing Italian ryegrass (Lolium multiflorum) over a significant portion of its life cycle. Diurnally fluctuating emissions of methanol and very small acetaldehyde fluxes were observed up to the cutting and removal of the grass. Methanol emissions were exponentially related to ambient temperatures and appeared to be higher during the grass’ rapid leaf area expansion and after a rain event. Acetaldehyde exchanges averaged over the whole period indicated very slow deposition. Our measurements confirm previous, similar results, as well as presumptions that grasses are comparatively low methanol emitters compared to non-grass species.

An ecosystem-scale perspective of the net land methanol flux: synthesis of micrometeorological flux measurements

Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of living plants as the major source and the reaction with OH as the major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates reflecting uncertainties in the approaches used to model, and the empirical data used to separately constrain these terms. Here we compiled micrometeorological methanol flux data from eight different study sites and reviewed the corresponding literature in order to provide a first cross-site synthesis of the terrestrial ecosystem-scale methanol exchange and present an independent data-driven view of the land–atmosphere methanol exchange. Our study shows that the controls of plant growth on the production, and thus the methanol emission magnitude, and stomatal conductance on the hourly methanol emission variability, established at the leaf level, hold across sites at the ecosystem-level. Unequivocal evidence for bi-directional methanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the formation of surface wetness. Methanol may adsorb to or dissolve in this surface water and eventually be chemically or biologically removed from it. Management activities in agriculture and forestry are shown to increase local methanol emission by orders of magnitude; they are however neglected at present in global budgets. While contemporary net land methanol budgets are overall consistent with the grand mean of the micrometeorological methanol flux measurements, we caution that the present approach of simulating methanol emission and deposition separately is prone to opposing systematic errors and does not allow taking full advantage of the rich information content of micrometeorological flux measurements.