scholarly journals On the sources and sinks of atmospheric VOCs: an integrated analysis of recent aircraft campaigns over North America

2019 ◽  
Vol 19 (14) ◽  
pp. 9097-9123 ◽  
Author(s):  
Xin Chen ◽  
Dylan B. Millet ◽  
Hanwant B. Singh ◽  
Armin Wisthaler ◽  
Eric C. Apel ◽  
...  
Keyword(s):  
North America ◽  
North American ◽  
Transport Model ◽  
Large Fraction ◽  
Oxidation Products ◽  
Biogenic Emissions ◽  
Integrated Analysis ◽  
Anthropogenic Emissions ◽  
Southeastern Us ◽  
Methyl Hydroperoxide

Abstract. We apply a high-resolution chemical transport model (GEOS-Chem CTM) with updated treatment of volatile organic compounds (VOCs) and a comprehensive suite of airborne datasets over North America to (i) characterize the VOC budget and (ii) test the ability of current models to capture the distribution and reactivity of atmospheric VOCs over this region. Biogenic emissions dominate the North American VOC budget in the model, accounting for 70 % and 95 % of annually emitted VOC carbon and reactivity, respectively. Based on current inventories anthropogenic emissions have declined to the point where biogenic emissions are the dominant summertime source of VOC reactivity even in most major North American cities. Methane oxidation is a 2× larger source of nonmethane VOCs (via production of formaldehyde and methyl hydroperoxide) over North America in the model than are anthropogenic emissions. However, anthropogenic VOCs account for over half of the ambient VOC loading over the majority of the region owing to their longer aggregate lifetime. Fires can be a significant VOC source episodically but are small on average. In the planetary boundary layer (PBL), the model exhibits skill in capturing observed variability in total VOC abundance (R2=0.36) and reactivity (R2=0.54). The same is not true in the free troposphere (FT), where skill is low and there is a persistent low model bias (∼ 60 %), with most (27 of 34) model VOCs underestimated by more than a factor of 2. A comparison of PBL : FT concentration ratios over the southeastern US points to a misrepresentation of PBL ventilation as a contributor to these model FT biases. We also find that a relatively small number of VOCs (acetone, methanol, ethane, acetaldehyde, formaldehyde, isoprene + oxidation products, methyl hydroperoxide) drive a large fraction of total ambient VOC reactivity and associated model biases; research to improve understanding of their budgets is thus warranted. A source tracer analysis suggests a current overestimate of biogenic sources for hydroxyacetone, methyl ethyl ketone and glyoxal, an underestimate of biogenic formic acid sources, and an underestimate of peroxyacetic acid production across biogenic and anthropogenic precursors. Future work to improve model representations of vertical transport and to address the VOC biases discussed are needed to advance predictions of ozone and SOA formation.

scholarly journals On the sources and sinks of atmospheric VOCs: An integrated analysis of recent aircraft campaigns over North America

2019 ◽  
Author(s):  
Xin Chen ◽  
Dylan B. Millet ◽  
Hanwant B. Singh ◽  
Armin Wisthaler ◽  
Eric C. Apel ◽  
...  
Keyword(s):  
North America ◽  
North American ◽  
Transport Model ◽  
Large Fraction ◽  
Oxidation Products ◽  
Biogenic Emissions ◽  
Integrated Analysis ◽  
Anthropogenic Emissions ◽  
Southeastern Us ◽  
Methyl Hydroperoxide

Abstract. We apply a high-resolution chemical transport model (GEOS-Chem CTM) with updated treatment of volatile organic compounds (VOCs) and a comprehensive suite of airborne datasets over North America to i) characterize the VOC budget, and ii) test the ability of current models to capture the distribution and reactivity of atmospheric VOCs, over this region. Biogenic emissions dominate the North American VOC budget in the model, accounting for 70 % and 95 % of annually emitted VOC-carbon and reactivity, respectively. Based on current inventories anthropogenic emissions have declined to the point where biogenic emissions are the dominant summertime source of VOC reactivity even in most major North American cities. Methane oxidation is a 2× larger source of non-methane VOCs (via production of formaldehyde and methyl hydroperoxide) over North America in the model than are anthropogenic emissions. However, anthropogenic VOCs account for over half the ambient VOC loading over the majority of the region owing to their longer aggregate lifetime. Fires can be a significant VOC source episodically but are small on average. In the planetary boundary layer (PBL), the model exhibits skill in capturing observed variability in total VOC-abundance (R2 = 0.36) and reactivity (R2 = 0.54). The same is not true in the free troposphere (FT), where skill is low and there is a persistent low model bias (~ 60 %), with most (27 of 34) model VOCs underestimated by more than a factor of 2. A comparison of PBL : FT concentration ratios over the southeastern US points to a misrepresentation of PBL ventilation as a contributor to these model FT biases. We also find that a relatively small number of VOCs (acetone, methanol, ethane, acetaldehyde, formaldehyde, isoprene + oxidation products, methyl hydroperoxide) drive a large fraction of total ambient VOC reactivity and associated model biases; research to improve understanding of their budgets is thus warranted. A source tracer analysis suggests a current overestimate of biogenic sources for hydroxyacetone, methyl ethyl ketone and glyoxal, an underestimate of biogenic formic acid sources, and an underestimate of peroxyacetic acid production across biogenic and anthropogenic precursors. Future work to improve model representations of vertical transport and to address the VOC biases discussed are needed to advance predictions of ozone and SOA formation.

scholarly journals Temperature-dependence of aerosol optical depth over the southeastern US

2016 ◽  
Author(s):  
Tero Mielonen ◽  
Anca Hienola ◽  
Thomas Kühn ◽  
Joonas Merikanto ◽  
Antti Lipponen ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Land Surface ◽  
Radiative Forcing ◽  
Climate Model ◽  
Biogenic Emissions ◽  
Anthropogenic Emissions ◽  
Model Estimate ◽  
Model Simulations ◽  
Southeastern Us ◽  
Biogenic Aerosols

Abstract. Previous studies have indicated that summer-time aerosol optical depths (AOD) over the southeastern US are dependent on temperature but the reason for this dependence and its radiative effects have so far been unclear. To quantify these effects we utilized AOD and land surface temperature (LST) products from the Advanced Along-Track Scanning Radiometer (AATSR) with observations of tropospheric nitrogen dioxide (NO2) column densities from the Ozone Monitoring Instrument (OMI). Furthermore, simulations of the global aerosol-climate model ECHAM-HAMMOZ have been used to identify the possible processes affecting aerosol loads and their dependence on temperature over the studied region. Our results showed that the level of AOD in the southeastern US is mainly governed by anthropogenic emissions but the observed temperature dependent behaviour is most likely originating from non-anthropogenic emissions. Model simulations indicated that biogenic emissions of volatile organic compounds (BVOC) can explain the observed temperature dependence of AOD. According to the remote sensing data sets, the non-anthropogenic contribution increases AOD by approximately 0.009 ± 0.018 K−1 while the modelled BVOC emissions increase AOD by 0.022 ± 0.002 K−1. Consequently, the regional direct radiative effect (DRE) of the non-anthropogenic AOD is −0.43 ± 0.88 W/m2/K and −0.17 ± 0.35 W/m2/K for clear- and all-sky conditions, respectively. The model estimate of the regional clear-sky DRE for biogenic aerosols is also in the same range: −0.86 ± 0.06 W/m2/K. These DRE values indicate significantly larger cooling than the values reported for other forested regions. Furthermore, the model simulations showed that biogenic emissions increased the number of biogenic aerosols with radius larger than 100 nm (N100, proxy for cloud condensation nuclei) by 28 % per one degree temperature increase. For the total N100, the corresponding increase was 4 % which implies that biogenic emissions could also have a small effect on indirect radiative forcing in this region.

scholarly journals Source attribution of Arctic black carbon constrained by aircraft and surface measurements

2017 ◽  
Vol 17 (19) ◽  
pp. 11971-11989 ◽  
Author(s):  
Jun-Wei Xu ◽  
Randall V. Martin ◽  
Andrew Morrow ◽  
Sangeeta Sharma ◽  
Lin Huang ◽  
...  
Keyword(s):  
North America ◽  
Biomass Burning ◽  
Western Siberia ◽  
Transport Model ◽  
Chemical Transport ◽  
The Arctic ◽  
Anthropogenic Emissions ◽  
Chemical Transport Model ◽  
Northern Asia ◽  
Airborne Measurements

Abstract. Black carbon (BC) contributes to Arctic warming, yet sources of Arctic BC and their geographic contributions remain uncertain. We interpret a series of recent airborne (NETCARE 2015; PAMARCMiP 2009 and 2011 campaigns) and ground-based measurements (at Alert, Barrow and Ny-Ålesund) from multiple methods (thermal, laser incandescence and light absorption) with the GEOS-Chem global chemical transport model and its adjoint to attribute the sources of Arctic BC. This is the first comparison with a chemical transport model of refractory BC (rBC) measurements at Alert. The springtime airborne measurements performed by the NETCARE campaign in 2015 and the PAMARCMiP campaigns in 2009 and 2011 offer BC vertical profiles extending to above 6 km across the Arctic and include profiles above Arctic ground monitoring stations. Our simulations with the addition of seasonally varying domestic heating and of gas flaring emissions are consistent with ground-based measurements of BC concentrations at Alert and Barrow in winter and spring (rRMSE  < 13 %) and with airborne measurements of the BC vertical profile across the Arctic (rRMSE  = 17 %) except for an underestimation in the middle troposphere (500–700 hPa).Sensitivity simulations suggest that anthropogenic emissions in eastern and southern Asia have the largest effect on the Arctic BC column burden both in spring (56 %) and annually (37 %), with the largest contribution in the middle troposphere (400–700 hPa). Anthropogenic emissions from northern Asia contribute considerable BC (27 % in spring and 43 % annually) to the lower troposphere (below 900 hPa). Biomass burning contributes 20 % to the Arctic BC column annually.At the Arctic surface, anthropogenic emissions from northern Asia (40–45 %) and eastern and southern Asia (20–40 %) are the largest BC contributors in winter and spring, followed by Europe (16–36 %). Biomass burning from North America is the most important contributor to all stations in summer, especially at Barrow.Our adjoint simulations indicate pronounced spatial heterogeneity in the contribution of emissions to the Arctic BC column concentrations, with noteworthy contributions from emissions in eastern China (15 %) and western Siberia (6.5 %). Although uncertain, gas flaring emissions from oilfields in western Siberia could have a striking impact (13 %) on Arctic BC loadings in January, comparable to the total influence of continental Europe and North America (6.5 % each in January). Emissions from as far as the Indo-Gangetic Plain could have a substantial influence (6.3 % annually) on Arctic BC as well.

scholarly journals Interpreting the variability of CO<sub>2</sub> columns over North America using a chemistry transport model: application to SCIAMACHY data

2008 ◽  
Vol 8 (2) ◽  
pp. 7339-7371 ◽  
Author(s):  
P. I. Palmer ◽  
M. P. Barkley ◽  
P. S. Monks
Keyword(s):  
North America ◽  
North American ◽  
Significant Contribution ◽  
Transport Model ◽  
Model Bias ◽  
Chemistry Transport Model ◽  
Mixing Ratios ◽  
Non Local ◽  
Flux Estimation ◽  
Kernel Model

Abstract. We use the GEOS-Chem chemistry transport model to interpret variability of CO2 columns and associated column-averaged volume mixing ratios (CVMRs) observed by the SCIAMACHY satellite instrument during the 2003 North American growing season, accounting for the instrument averaging kernel. Model and observed columns, largely determined by surface topography, averaged on a 2°×2.5° grid, are in excellent agreement (model bias=3%, r>0.9), as expected. Model and observed CVMRs, determined by scaling column CO2 by surface pressure data, are on average within 3% but are only weakly correlated, reflecting a large positive model bias (10–15 ppmv) at 50–70° N during midsummer at the peak of biospheric uptake. GEOS-Chem generally reproduces the magnitude and seasonal cycle of observed CO2 surface VMRs across North America. During midsummer we find that model CVMRs and surface VMRs converge, reflecting the instrument vertical sensitivity and the strong influence of the land biosphere on lower tropospheric CO2 columns. We use model tagged tracers to show that local fluxes largely determine CVMR variability over North America, with the largest individual CVMR contributions (1.1%) from the land biosphere. Fuel sources are relatively constant while biomass burning make a significant contribution only during midsummer. We also show that non-local sources contribute significantly to total CVMRs over North America, with the boreal Asian land biosphere contributing close to 1% in midsummer at high latitudes. We used the monthly-mean Jacobian matrix for North America to illustrate that: 1) North American CVMRs represent a superposition of many weak flux signatures, but differences in flux distributions should permit independent flux estimation; and 2) the atmospheric e-folding lifetimes for many of these flux signatures are 3–4 months, beyond which time they are too well-mixed to interpret.

scholarly journals Current estimates of biogenic emissions from Eucalypts uncertain for Southeast Australia

2016 ◽  
Author(s):  
K. M. Emmerson ◽  
I. E. Galbally ◽  
A. B. Guenther ◽  
C. Paton-Walsh ◽  
E.-A. Guerette ◽  
...  
Keyword(s):  
Transport Model ◽  
Chemical Species ◽  
Field Measurements ◽  
Oxidation Products ◽  
Biogenic Emissions ◽  
Emission Rates ◽  
Chemical Transport Model ◽  
Southeast Australia ◽  
Unusual Position ◽  
Adult Trees

Abstract. The biogenic emissions of isoprene and monoterpenes are one of the main drivers of atmospheric photochemistry, including oxidant and secondary organic aerosol production. In this paper, the emission rates of isoprene and monoterpenes from Australian vegetation are investigated for the first time using the Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGANv2.1), the CSIRO chemical transport model, and atmospheric observations of isoprene, monoterpenes and isoprene oxidation products (methacrolein and methyl-vinyl-ketone). Observations from four field campaigns during three different seasons are used, covering urban, coastal suburban and inland forest areas. The observed concentrations of isoprene and monoterpenes were of a broadly similar magnitude, which may indicate that southeast Australia holds an unusual position where neither chemical species dominates. The model results overestimate the observed atmospheric concentrations of isoprene (up to a factor of 6) and underestimate the monoterpene concentrations (up to a factor of 4). This may occur because the emission rates currently used in MEGANv2.1 for Australia are drawn mainly from young Eucalypt trees (< 7 years), which may emit more isoprene than adult trees. There is no single increase/decrease factor for the emissions which suits all seasons and conditions studied. There is a need for further field measurements of in-situ isoprene and monoterpene emission fluxes in Australia.

scholarly journals Interpreting the variability of space-borne CO<sub>2</sub> column-averaged volume mixing ratios over North America using a chemistry transport model

2008 ◽  
Vol 8 (19) ◽  
pp. 5855-5868 ◽  
Author(s):  
P. I. Palmer ◽  
M. P. Barkley ◽  
P. S. Monks
Keyword(s):  
North America ◽  
North American ◽  
Significant Contribution ◽  
Transport Model ◽  
Co2 Flux ◽  
Chemistry Transport Model ◽  
Sources And Sinks ◽  
Mixing Ratios ◽  
Non Local ◽  
Flux Estimation

Abstract. We use the GEOS-Chem chemistry transport model to interpret the sources and sinks of CO2 that determine variability of column-averaged volume mixing ratios (CVMRs), as observed by the SCIAMACHY satellite instrument, during the 2003 North American growing season. GEOS-Chem generally reproduces the magnitude and seasonal cycle of observed CO2 surface VMRs across North America and is quantitatively consistent with column VMRs in later years. However, it cannot reproduce the magnitude or variability of FSI-WFM-DOAS SCIAMACHY CVMRs. We use model tagged tracers to show that local fluxes largely determine CVMR variability over North America, with the largest individual CVMR contributions (1.1%) from the land biosphere. Fuel sources are relatively constant while biomass burning makes a significant contribution only during midsummer. We also show that non-local sources contribute significantly to total CVMRs over North America, with the boreal Asian land biosphere contributing close to 1% in midsummer at high latitudes. We used the monthly-mean Jacobian matrix for North America to illustrate that:~1) North American CVMRs represent a superposition of many weak flux signatures, but differences in flux distributions should permit independent flux estimation; and 2) the atmospheric e-folding lifetimes for many of these flux signatures are 3–4 months, beyond which time they are too well-mixed to interpret. These long lifetimes will improve the efficacy of observed CVMRs as surface CO2 flux constraints.

scholarly journals Nested-grid simulation of mercury over North America

2012 ◽  
Vol 12 (14) ◽  
pp. 6095-6111 ◽  
Author(s):  
Y. Zhang ◽  
L. Jaeglé ◽  
A. van Donkelaar ◽  
R. V. Martin ◽  
C. D. Holmes ◽  
...  
Keyword(s):  
North America ◽  
North American ◽  
Wet Deposition ◽  
Atmospheric Mercury ◽  
Point Sources ◽  
Anthropogenic Emissions ◽  
Spatial And Temporal Variability ◽  
Nested Model ◽  
The Us ◽  
Nested Grid

Abstract. We have developed a new nested-grid mercury (Hg) simulation over North America with a 1/2° latitude by 2/3° longitude horizontal resolution employing the GEOS-Chem global chemical transport model. Emissions, chemistry, deposition, and meteorology are self-consistent between the global and nested domains. Compared to the global model (4° latitude by 5° longitude), the nested model shows improved skill at capturing the high spatial and temporal variability of Hg wet deposition over North America observed by the Mercury Deposition Network (MDN) in 2008–2009. The nested simulation resolves features such as higher deposition due to orographic precipitation, land/ocean contrast and and predicts more efficient convective rain scavenging of Hg over the southeast United States. However, the nested model overestimates Hg wet deposition over the Ohio River Valley region (ORV) by 27%. We modify anthropogenic emission speciation profiles in the US EPA National Emission Inventory (NEI) to account for the rapid in-plume reduction of reactive to elemental Hg (IPR simulation). This leads to a decrease in the model bias to −2.3% over the ORV region. Over the contiguous US, the correlation coefficient (r) between MDN observations and our IPR simulation increases from 0.60 to 0.78. The IPR nested simulation generally reproduces the seasonal cycle in surface concentrations of speciated Hg from the Atmospheric Mercury Network (AMNet) and Canadian Atmospheric Mercury Network (CAMNet). In the IPR simulation, annual mean gaseous and particulate-bound Hg(II) are within 140% and 11% of observations, respectively. In contrast, the simulation with unmodified anthropogenic Hg speciation profiles overestimates these observations by factors of 4 and 2 for gaseous and particulate-bound Hg(II), respectively. The nested model shows improved skill at capturing the horizontal variability of Hg observed over California during the ARCTAS aircraft campaign. The nested model suggests that North American anthropogenic emissions account for 10–22% of Hg wet deposition flux over the US, depending on the anthropogenic emissions speciation profile assumed. The modeled percent contribution can be as high as 60% near large point sources in ORV. Our results indicate that the North American anthropogenic contribution to dry deposition is 13–20%.

scholarly journals Observations of oxidation products above a forest imply biogenic emissions of very reactive compounds

2005 ◽  
Vol 5 (1) ◽  
pp. 67-75 ◽  
Author(s):  
R. Holzinger ◽  
A. Lee ◽  
K. T. Paw ◽  
U. A. H. Goldstein
Keyword(s):  
Ponderosa Pine ◽  
Forest Canopy ◽  
Large Fraction ◽  
Oxidation Products ◽  
Biogenic Emissions ◽  
Central California ◽  
Mixing Ratios ◽  
Volatile Organic ◽  
Current Emission ◽  
Ponderosa Pine Forest

Abstract. Vertical gradients of mixing ratios of volatile organic compounds have been measured in a Ponderosa pine forest in Central California (38.90° N, 120.63° W, 1315m). These measurements reveal large quantities of previously unreported oxidation products of short lived biogenic precursors. The emission of biogenic precursors must be in the range of 13-66µmol m-2h-1 to produce the observed oxidation products. That is 6-30 times the emissions of total monoterpenes observed above the forest canopy on a molar basis. These reactive precursors constitute a large fraction of biogenic emissions at this site, and are not included in current emission inventories. When oxidized by ozone they should efficiently produce secondary aerosol and hydroxyl radicals.

scholarly journals GNAQPMS-Hg v1.0, a global nested atmospheric mercury transport model: model description, evaluation and application to trans-boundary transport of Chinese anthropogenic emissions

2015 ◽  
Vol 8 (9) ◽  
pp. 2857-2876 ◽  
Author(s):  
H. S. Chen ◽  
Z. F. Wang ◽  
J. Li ◽  
X. Tang ◽  
B. Z. Ge ◽  
...  
Keyword(s):  
North America ◽  
East Asia ◽  
Aqueous Phase ◽  
Wet Deposition ◽  
Transport Model ◽  
Atmospheric Mercury ◽  
Model Description ◽  
Anthropogenic Emissions ◽  
Comparison Results ◽  
Western Asia

Abstract. Atmospheric mercury (Hg) is a toxic pollutant and can be transported over the whole globe due to its long lifetime in the atmosphere. For the purpose of assessing Hg hemispheric transport and better characterizing regional Hg pollution, a global nested atmospheric Hg transport model (GNAQPMS-Hg – Global Nested Air Quality Prediction Modeling System for Hg) has been developed. In GNAQPMS-Hg, the gas- and aqueous-phase Hg chemistry representing the transformation among three forms of Hg: elemental mercury (Hg(0)), divalent mercury (Hg(II)), and primary particulate mercury (Hg(P)) are calculated. A detailed description of the model, including mercury emissions, gas- and aqueous-phase chemistry, and dry and wet deposition is given in this study. Worldwide observations including extensive data in China have been collected for model evaluation. Comparison results show that the model reasonably simulates the global mercury budget and the spatiotemporal variation of surface mercury concentrations and deposition. Overall, model predictions of annual total gaseous mercury (TGM) and wet deposition agree with observations within a factor of 2, and within a factor of 5 for oxidized mercury and dry deposition. The model performs significantly better in North America and Europe than in East Asia. This can probably be attributed to the large uncertainties in emission inventories, coarse model resolution and to the inconsistency between the simulation and observation periods in East Asia. Compared to the global simulation, the nested simulation shows improved skill at capturing the high spatial variability of surface Hg concentrations and deposition over East Asia. In particular, the root mean square error (RMSE) of simulated Hg wet deposition over East Asia is reduced by 24 % in the nested simulation. Model sensitivity studies indicate that Chinese primary anthropogenic emissions account for 30 and 62 % of surface mercury concentrations and deposition over China, respectively. Along the rim of the western Pacific, the contributions from Chinese sources are 11 and 15.2 % over the Korean Peninsula, 10.4 and 8.2 % over Southeast Asia, and 5.7 and 5.9 % over Japan. But for North America, Europe and western Asia, the contributions from China are all below 5 %.

scholarly journals Current estimates of biogenic emissions from eucalypts uncertain for southeast Australia

2016 ◽  
Vol 16 (11) ◽  
pp. 6997-7011 ◽  
Author(s):  
Kathryn M. Emmerson ◽  
Ian E. Galbally ◽  
Alex B. Guenther ◽  
Clare Paton-Walsh ◽  
Elise-Andree Guerette ◽  
...  
Keyword(s):  
Transport Model ◽  
Chemical Species ◽  
Field Measurements ◽  
Oxidation Products ◽  
Biogenic Emissions ◽  
Emission Rates ◽  
Chemical Transport Model ◽  
Southeast Australia ◽  
Unusual Position ◽  
Adult Trees

Abstract. The biogenic emissions of isoprene and monoterpenes are one of the main drivers of atmospheric photochemistry, including oxidant and secondary organic aerosol production. In this paper, the emission rates of isoprene and monoterpenes from Australian vegetation are investigated for the first time using the Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGANv2.1); the CSIRO chemical transport model; and atmospheric observations of isoprene, monoterpenes and isoprene oxidation products (methacrolein and methyl vinyl ketone). Observations from four field campaigns during three different seasons are used, covering urban, coastal suburban and inland forest areas. The observed concentrations of isoprene and monoterpenes were of a broadly similar magnitude, which may indicate that southeast Australia holds an unusual position where neither chemical species dominates. The model results overestimate the observed atmospheric concentrations of isoprene (up to a factor of 6) and underestimate the monoterpene concentrations (up to a factor of 4). This may occur because the emission rates currently used in MEGANv2.1 for Australia are drawn mainly from young eucalypt trees (< 7 years), which may emit more isoprene than adult trees. There is no single increase/decrease factor for the emissions which suits all seasons and conditions studied. There is a need for further field measurements of in situ isoprene and monoterpene emission fluxes in Australia.

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