scholarly journals Underway seawater and atmospheric measurements of volatile organic compounds in the Southern Ocean

2020 ◽  
Vol 17 (9) ◽  
pp. 2593-2619 ◽  
Author(s):  
Charel Wohl ◽  
Ian Brown ◽  
Vassilis Kitidis ◽  
Anna E. Jones ◽  
William T. Sturges ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Southern Ocean ◽  
Organic Compounds ◽  
Dimethyl Sulfide ◽  
Ambient Air ◽  
Atmospheric Measurements ◽  
Mixing Ratios ◽  
Volatile Organic ◽  
Air Mixing ◽  
Net Flux

Abstract. Dimethyl sulfide and volatile organic compounds (VOCs) are important for atmospheric chemistry. The emissions of biogenically derived organic gases, including dimethyl sulfide and especially isoprene, are not well constrained in the Southern Ocean. Due to a paucity of measurements, the role of the ocean in the atmospheric budgets of atmospheric methanol, acetone, and acetaldehyde is even more poorly known. In order to quantify the air–sea fluxes of these gases, we measured their seawater concentrations and air mixing ratios in the Atlantic sector of the Southern Ocean, along a ∼ 11 000 km long transect at approximately 60∘ S in February–April 2019. Concentrations, oceanic saturations, and estimated fluxes of five simultaneously sampled gases (dimethyl sulfide, isoprene, methanol, acetone, and acetaldehyde) are presented here. Campaign mean (±1σ) surface water concentrations of dimethyl sulfide, isoprene, methanol, acetone, and acetaldehyde were 2.60 (±3.94), 0.0133 (±0.0063), 67 (±35), 5.5 (±2.5), and 2.6 (±2.7) nmol dm−3 respectively. In this dataset, seawater isoprene and methanol concentrations correlated positively. Furthermore, seawater acetone, methanol, and isoprene concentrations were found to correlate negatively with the fugacity of carbon dioxide, possibly due to a common biological origin. Campaign mean (±1σ) air mixing ratios of dimethyl sulfide, isoprene, methanol, acetone, and acetaldehyde were 0.17 (±0.09), 0.053 (±0.034), 0.17 (±0.08), 0.081 (±0.031), and 0.049 (±0.040) ppbv. We observed diel changes in averaged acetaldehyde concentrations in seawater and ambient air (and to a lesser degree also for acetone and isoprene), which suggest light-driven production. Campaign mean (±1σ) fluxes of 4.3 (±7.4) µmol m−2 d−1 DMS and 0.028 (±0.021) µmol m−2 d−1 isoprene are determined where a positive flux indicates from the ocean to the atmosphere. Methanol was largely undersaturated in the surface ocean with a mean (±1σ) net flux of −2.4 (±4.7) µmol m−2 d−1, but it also had a few occasional episodes of outgassing. This section of the Southern Ocean was found to be a source and a sink for acetone and acetaldehyde this time of the year, depending on location, resulting in a mean net flux of −0.55 (±1.14) µmol m−2 d−1 for acetone and −0.28 (±1.22) µmol m−2 d−1 for acetaldehyde. The data collected here will be important for constraining the air–sea exchange, cycling, and atmospheric impact of these gases, especially over the Southern Ocean.

scholarly journals Underway seawater and atmospheric measurements of volatile organic compounds in the Southern Ocean

2020 ◽  
Author(s):  
Charel Wohl ◽  
Ian Brown ◽  
Vassilis Kitidis ◽  
Anna E. Jones ◽  
William T. Sturges ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Southern Ocean ◽  
Organic Compounds ◽  
Dimethyl Sulfide ◽  
Ambient Air ◽  
Atmospheric Measurements ◽  
Biological Origin ◽  
Mixing Ratios ◽  
Volatile Organic ◽  
Air Mixing

Abstract. Dimethyl sulfide and volatile organic compounds and are important for atmospheric chemistry. The oceanic emissions of biogenically derived gases, including dimethyl sulfide and especially isoprene, are not well constrained. The role of the ocean in the global budgets of atmospheric methanol, acetone and acetaldehyde is even more poorly known. In order to quantify the air-sea fluxes of these gases we measured their seawater concentrations and air mixing ratios in the Atlantic sector of the Southern Ocean, along a ~ 11 000 km long transect at approximately 60° S in Feb–Apr 2019. Concentrations, oceanic saturations and estimated fluxes of several simultaneously sampled volatile organic compounds (methanol, acetone, acetaldehyde, dimethyl sulfide and isoprene) are presented here. Campaign mean (± 1σ) surface water concentrations of dimethyl sulfide, isoprene, methanol, acetone and acetaldehyde were 2.60 (± 3.94), 0.0133 (± 0.0063), 67 (± 35), 5.5 (± 2.5) and 2.6 (± 2.7) nmol dm−3 respectively. In this dataset, seawater isoprene and methanol concentrations correlated positively. Furthermore, seawater acetone, methanol and isoprene concentrations were found to correlate negatively with the fugacity of carbon dioxide, possibly due to a common biological origin. Campaign mean (± 1σ) air mixing ratios of methanol, acetone and acetaldehyde were relatively low at 0.17 (± 0.08), 0.081 (± 0.031) and 0.049 (± 0.040) ppbv. We observed diel changes in averaged acetaldehyde concentrations in seawater and ambient air (and to a lesser degree also for acetone and isoprene), which suggest light-driven productions. Campaign mean (± 1σ) fluxes of 4.3 (± 7.4) µmol m−2 d−1 DMS and 0.028 (± 0.021) µmol m−2 d−1 isoprene are determined where a positive flux indicates from the ocean to the atmosphere. Methanol was largely undersaturated in the surface ocean with a mean (± 1σ) net flux of −2.4 (± 4.7) µmol m−2 d−1, but also had a few occasional episodes of outgassing This section of the Southern Ocean was found to be both a source and a sink for acetone and acetaldehyde this time of the year, depending on location, resulting in a mean flux of −0.55 (± 1.15) µmol m−2 d−1 for acetone and −0.28 (± 1.22) µmol m−2 d−1 for acetaldehyde. The data collected here will be important for constraining the oceanic source/sink of these gases and potentially help to elucidate the presence of common sources/sinks for these compounds.

scholarly journals Diel and seasonal changes of biogenic volatile organic compounds within and above an Amazonian rainforest

2015 ◽  
Vol 15 (6) ◽  
pp. 3359-3378 ◽  
Author(s):  
A. M. Yáñez-Serrano ◽  
A. C. Nölscher ◽  
J. Williams ◽  
S. Wolff ◽  
E. Alves ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Ambient Air ◽  
Dry Season ◽  
Solar Irradiation ◽  
Biogenic Volatile Organic Compounds ◽  
Wet Season ◽  
Mixing Ratios ◽  
Volatile Organic ◽  
Amazonian Rainforest

Abstract. The Amazonian rainforest is a large tropical ecosystem, which is one of the last pristine continental terrains. This ecosystem is ideally located for the study of diel and seasonal behaviour of biogenic volatile organic compounds (BVOCs) in the absence of local human interference. In this study, we report the first atmospheric BVOC measurements at the Amazonian Tall Tower Observatory (ATTO) site, located in central Amazonia. A quadrupole proton-transfer-reaction mass spectrometer (PTR-MS), with seven ambient air inlets, positioned from near ground to about 80 m (0.05, 0.5, 4, 24, 38, 53 and 79 m above the forest floor), was deployed for BVOC monitoring. We report diel and seasonal (February–March 2013 as wet season and September 2013 as dry season) ambient mixing ratios for isoprene, monoterpenes, isoprene oxidation products, acetaldehyde, acetone, methyl ethyl ketone (MEK), methanol and acetonitrile. Clear diel and seasonal patterns were observed for all compounds. In general, lower mixing ratios were observed during night, while maximum mixing ratios were observed during the wet season (February–March 2013), with the peak in solar irradiation at 12:00 LT (local time) and during the dry season (September 2013) with the peak in temperature at 16:00 LT. Isoprene and monoterpene mixing ratios were the highest within the canopy with a median of 7.6 and 1 ppb, respectively (interquartile range (IQR) of 6.1 and 0.38 ppb) during the dry season (at 24 m, from 12:00 to 15:00 LT). The increased contribution of oxygenated volatile organic compounds (OVOCs) above the canopy indicated a transition from dominating forest emissions during the wet season (when mixing ratios were higher than within the canopy), to a blend of biogenic emission, photochemical production and advection during the dry season when mixing ratios were higher above the canopy. Our observations suggest strong seasonal interactions between environmental (insolation, temperature) and biological (phenology) drivers of leaf BVOC emissions and atmospheric chemistry. Considerable differences in the magnitude of BVOC mixing ratios, as compared to other reports of Amazonian BVOC, demonstrate the need for long-term observations at different sites and more standardized measurement procedures, in order to better characterize the natural exchange of BVOCs between the Amazonian rainforest and the atmosphere.

scholarly journals Quantifying the uncertainty in simulating global tropospheric composition due to the variability in global emission estimates of Biogenic Volatile Organic Compounds

2013 ◽  
Vol 13 (5) ◽  
pp. 2857-2891 ◽  
Author(s):  
J. E. Williams ◽  
P. F. J. van Velthoven ◽  
C. A. M. Brenninkmeijer
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Global Distribution ◽  
Chemical Mechanism ◽  
Biogenic Volatile Organic Compounds ◽  
Atmospheric Measurements ◽  
Large Variability ◽  
Mixing Ratios ◽  
Volatile Organic ◽  
Tropospheric O3

Abstract. The emission of organic compounds from biogenic processes acts as an important source of trace gases in remote regions away from urban conurbations, and is likely to become more important in future decades due to the further mitigation of anthropogenic emissions that affect air quality and climate forcing. In this study we examine the contribution of biogenic volatile organic compounds (BVOCs) towards global tropospheric composition using the global 3-D chemistry transport model TM5 and the recently developed modified CB05 chemical mechanism. By comparing regional BVOC emission estimates we show that biogenic processes act as dominant sources for many regions and exhibit a large variability in the annually and seasonally integrated emission fluxes. By performing sensitivity studies we find that the contribution of BVOC species containing between 1 to 3 carbon atoms has an impact on the resident mixing ratios of tropospheric O3 and CO, accounting for ~2.5% and ~10.8% of the simulated global distribution, respectively. This is approximately a third of the cumulative effect introduced by isoprene and the monoterpenes. By examining an ensemble of 3-D global chemistry transport simulations which adopt different global BVOC emission inventories we determine the associated uncertainty introduced towards simulating the composition of the troposphere for the year 2000. By comparing the model ensemble values against a composite of atmospheric measurements we show that the effects on tropospheric O3 are limited to the lower troposphere (with an uncertainty between −2% to 10%), whereas that for tropospheric CO extends up to the upper troposphere (with an uncertainty of between 10 to 45%). Comparing the mixing ratios for low molecular weight alkenes in TM5 against surface measurements taken in Europe implies that the cumulative emission estimates are too low, regardless of the chosen BVOC inventory. This variability in the global distribution of CO due to BVOC emissions introduces an associated uncertainty in the tropospheric CO burden of 11.4%, which impacts strongly on the oxidative capacity of the troposphere, introducing an uncertainty in the atmospheric lifetime of the greenhouse gas CH4 of ~3.3%. This study thus identifies the necessity of placing further constraints on non-CH4 global biogenic emission estimates in large-scale global atmospheric chemistry models.

scholarly journals Diel and seasonal changes of Biogenic Volatile Organic Compounds within and above an Amazonian rainforest site

2014 ◽  
Vol 14 (21) ◽  
pp. 29159-29208 ◽  
Author(s):  
A. M. Yañez-Serrano ◽  
A. C. Nölscher ◽  
J. Williams ◽  
S. Wolff ◽  
E. Alves ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Ambient Air ◽  
Dry Season ◽  
Solar Irradiation ◽  
Biogenic Volatile Organic Compounds ◽  
Wet Season ◽  
Mixing Ratios ◽  
Volatile Organic ◽  
Amazonian Rainforest

Abstract. The Amazonian rainforest is a large tropical ecosystem, and is one of the last pristine continental terrains. This ecosystem is ideally located for the study of diel and seasonal behaviour of Biogenic Volatile Organic Compounds (BVOC) in the absence of local human interference. In this study, we report the first atmospheric BVOC measurements at the Amazonian Tall Tower Observatory (ATTO) site, located in Central Amazonia. A quadrupole Proton Transfer Reaction Mass Spectrometer (PTR-MS) with 7 ambient air inlets, positioned from near the ground to about 80 m (0.05, 0.5, 4, 24, 38, 53 and 79 m above the forest floor), was deployed for BVOC monitoring. We report diel and seasonal (February/March 2013 and September 2013) ambient mixing ratios for isoprene, monoterpenes, methyl vinyl ketone (MVK) + methacrolein (MACR), acetaldehyde, acetone, methyl ethyl ketone (MEK), methanol and acetonitrile. Clear diel and seasonal patterns were observed for all compounds during the study. In general, lower mixing ratios were observed during night, while maximum mixing ratios were observed with the peak in solar irradiation at 12:00 LT during the wet season (February/March 2013), and with the peak in temperature at 16:00 LT during the dry season (September 2013). Isoprene mixing ratios were highest within the canopy with a median of 7.6 ppb and interquartile range (IQR) of 6.1 ppb (dry season at 24 m, from 12:00–15:00). Monoterpene mixing ratios were higher than previously reported for any Amazonian rainforest ecosystem (median 1 ppb, IQR 0.38 ppb during the dry season at 24 m from 15:00–18:00). Oxygenated Volatile Organic Compound (OVOC) patterns indicated a transition from dominating forest emissions during the wet season to a blend of biogenic emission, photochemical production, and advection during the dry season. This was inferred from the high mixing ratios found within the canopy, and those obtained above the canopy for the wet and dry season, respectively. Our observations reveal strong seasonal BVOC patterns and oxidation capacity, reflected in the different vertical profiles obtained between the dry and wet season, most likely driven by insolation, temperature and phenology. In addition, significant differences to other reports of Amazonian BVOC demonstrate the need for long-term observations and more standardized measurement procedures in order to better understand the natural exchange of BVOC between the Amazonian rainforest and the atmosphere.

scholarly journals Quantifying the uncertainty in simulating global tropospheric composition due to the variability in global emission estimates of Biogenic Volatile Organic Compounds

2012 ◽  
Vol 12 (11) ◽  
pp. 28765-28836
Author(s):  
J. E. Williams ◽  
P. F. J. van Velthoven ◽  
C. A. M. Brenninkmeijer
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Global Distribution ◽  
Chemical Mechanism ◽  
Biogenic Volatile Organic Compounds ◽  
Atmospheric Measurements ◽  
Large Variability ◽  
Mixing Ratios ◽  
Volatile Organic ◽  
Tropospheric O3

Abstract. The emission of organic compounds from biogenic processes acts as an important source of trace gases in remote regions away from urban conurbations, and is likely to become more important in future decades due to the further mitigation of anthropogenic emissions that affect air quality and climate forcing. In this study we examine the contribution of biogenic volatile organic compounds (BVOCs) towards global tropospheric composition using the global 3-D chemistry transport model TM5 and the recently developed modified CB05 chemical mechanism. By comparing regional BVOC emission estimates we show that biogenic processes act as dominant sources for many regions and exhibit a large variability in the annually and seasonally integrated emission fluxes. By performing sensitivity studies we find that the contribution of BVOC species containing between 1 to 3 carbon atoms has an impact on the resident mixing ratios of tropospheric O3 and CO, accounting for ~3% and ~11% of the simulated global distribution, respectively. This is approximately a third of the cumulative effect introduced by isoprene and the monoterpenes. By examining an ensemble of 3-D global chemistry-transport simulations which adopt different global BVOC emission inventories we determine the associated uncertainty introduced towards simulating the composition of the troposphere for the year 2000. By comparing the model ensemble values against a~composite of atmospheric measurements we show that the effects on tropospheric O3 are limited to the lower troposphere (with an uncertainty between −2% to 10%), whereas that for tropospheric CO extends up to the upper troposphere (with an uncertainty of between 10 to 45%). Comparing the mixing ratios for low molecular weight alkenes in TM5 against surface measurements taken in Europe implies that the cumulative emission estimates are too low, regardless of the chosen BVOC inventory. This variability in the global distribution of CO due to BVOC emissions introduces an associated uncertainty in the tropospheric CO burden of ~11%, which impacts strongly on the oxidative capacity of the troposphere, introducing an uncertainty in the atmospheric lifetime of the greenhouse gas CH4 of ~3%. This study thus identifies the necessity of placing further constraints on non-CH4 global biogenic emission estimates in large-scale global atmospheric chemistry models.

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