1. The First Global Evaluation of Dissolved Organic Carbon
Sarah Safieddine and Colette Heald
05/01/2017

2. Emissions [TgCyr-1] Deposition [TgCyr-1]
The Reactive Organic Carbon (ROC) is Essential for Tropospheric Chemistry
Safieddine, Heald, and Henderson, 2017
CH4
oxidation
Emissions [TgCyr-1]
Biogenic
Anthropogenic/biofuel
Biomass
Oceans(net)
NMVOC: 15 TgC
OA : 1 TgC
Deposition [TgCyr-1] CO
905 TgCyr-1
Emissions
[TgCyr-1]
400
ROC
515 TgCyr-1
415 TgCyr-1
370 TgCyr-1
CO2
1275 TgCyr-1
935 TgCyr-1
460 TgCyr-1
Improving the understanding of the composition and evolution of dissolved organic carbon (DOC) will therefore provide constraints on atmospheric reactive organic carbon (ROC) lifecycle
Wet: 272
Dry: 188
ROC is simulated by expanding the GEOS-Chem standard simulation, including:
new emissions and chemistry, expanding the wet and dry deposition scheme, and ensuring carbon closure.

3. Seasonal Dissolved Organic Carbon (DOC)
DJF
JJA
Rain
[mm/day]
Atmospheric Reactive Organic Carbon (ROC) Column Concentration [µgC/m2]
Dissolved Organic
Carbon (DOC)
concentration
[mgC/L]
The global DOC is calculated from the wet deposition flux of atmospheric reactive carbon divided by the global precipitation.

4. DOC Simulated vs Observed: Surprisingly Good Agreement!
Iavorivska et al., 2016
Comparison of the 2010 simulated DOC with a 30-year record of available DOC measurements over different environments and regions, shows a good correlation
(r= 0.67) with simulated DOC values underestimating the observation by 34%.

5. Average Carbon Oxidation State: Derived by GEOS-Chem, Measured by AMS
The average carbon oxidation state is metric for the degree of oxidation of atmospheric organic species, a quantity that necessarily increases upon oxidation
Kroll et al., 2011
Explain x and y axis here Higher organics carbon number are lumped
Mass spectrometry techniques provide key information on the chemical composition of organics, such as the average carbon oxidation state, which can be derived from GEOS-Chem.
Mass Spectrometry techniques provide key

6. First Average Carbon Oxidation State (OSc) Derived From a Model
we lump thing so less species than in the kroll diagram.
In the dissolved form, DOC OSc is generally higher than ROC OSc due to increase of solubility upon oxidation

7. The First Simulated Spatial Average Carbon Oxidation State
Safieddine and Heald, in prep
In the atmosphere, ROC OSc is governed by alkanes with lower photochemistry (oxidation) leading to a lower OSc in winter of the Northern Hemisphere
In the dissolved form, DOC OSc is more uniform and generally higher than ROC OSc due to increase of solubility upon oxidation

8. Conclusions and Future Work
Wet deposition is the largest physical sink of reactive organic carbon
Improving the understanding of the composition and evolution of dissolved organic carbon (DOC) will therefore provide constraints on atmospheric reactive organic carbon (ROC) lifecycle
DOC depends on local sources and chemical processing of reactive organic carbon, as well as precipitation
Precipitation
Dissolved Organic
Carbon
ROC is dominated by chemically reduced hydrocarbons and acetone and DOC is dominated globally by semi-volatiles, formaldehyde, and POA.
𝑂𝑆 𝑐 is negative for most of ROC and DOC compounds and is higher in dissolved form due to increase of solubility upon oxidation.
Focus on the US: analysis of NADP data will provide DOC values and information on the sample chemical composition for model evaluation.