Sulfur cycle and oxidation chemistry of marine DMS at kCGBAPS
Abitha, Alanah, Caleb, Simon, Sive and Robyn
Some background - DMS chemistry
Understanding DMS chemistry - radiation biases present in current models.
DMS oxidation products namely MSA, SA their origin (coastal/marine), concentrations as a function of air mass history (HYSPLIT back trajectories, radon measurements), concentration of ozone (radicals that aid oxidation), box models to present the whole story.
The questions we want to ask
In order to understand DMS chemistry better, we want to look at:
1. Diurnal variability: Day/night, amount of radiation
2. Temperature, maybe(?) relative humidity
3. Air mass history
4. Oxidation chemistry pathways and photolysis
Data used
PTR-ToF-MS (gas)
-> Dimethyl sulfide (DMS)
HR-ToF-AMS (aerosol)
-> Methanesulfonic acid (MSA)
NO3-ToF-CIMS (gas)
-> Methanesulfonic acid (MSA)
-> Sulfuric acid (SA)
MODIS retrievals aboard the NASA Aqua and Terra satellite
We discovered interesting events in Nov 2024…
SA (g)
MSA (g)
DMS (g)
MSA (p)
HYSPLIT Back-trajectory (23rd, 24th Nov, 2024 10m-AGL- Meter Above the Ground Level- UTC)
We discovered interesting events in Nov 2024…
Event 1
Event 2
EVENT 1
South coastal influence
24 Nov 2024
The wind direction shifted from easterly to south-westerly
Local time (AEST)
In baseline sector, but not necessarily baseline
Local time (AEST)
We observed 1 ppb DMS, coinciding with increases in MSA (gas + aerosol)
DMS (g)
MSA (g)
MSA (p)
DMS vs MSA (AMS)
CIMS
AMS
PTR
DMS correlated reasonably well with MSA (gas-phase)
DMS vs MSA (CIMS)
This occurred when winds switched to SE/SW coastal
23rd
24th
AMS
PTR DMS
High DMS + MSA associated with lower wind speeds in SW
i.e. within the baseline sector but likely had previous coastal influence
CIMS
High DMS + MSA associated with lower wind speeds in SW
Air Mass Back Trajectory on 2024/11/23 - 2024/11/24
Biological activity along the coastline - a potential source of DMS
When we saw a peak in DMS!
EVENT 2
North coastal influence
28 Nov 2024
The wind direction shifted from NW to NE
This coincided with ~2 ppb DMS + high MSA/SA
PTR DMS
CIMS SA
AMS MSA
CIMS MSA
This time it was cleaner, but not baseline
High DMS + MSA with lower wind speed from NW
PTR DMS
CIMS (ions/s)
HYSPLIT Back-trajectory (27th, 28th, Nov, 2024 10m-AGL- Meter Above the Ground Level- UTC)
18 UTC 27th
00 UTC 28th
06 UTC 28th
Insert Chl-a map
Biological activity, this time influenced by Robbins Island?
Event 02: 2024/11/27 & 2024/11/28
PyBox model
BOX MODEL
To be continued…
DMS chemistry in the box model
Conclusion
If you compare Event 1 (24th) and Event 2 (27th)
East -> SW
1 ppb DMS
High MSA (gas + aerosol)
Low SA
East -> NW
2 ppb DMS
High MSA (only gas)
High SA
Some Chemistry…
The primary production pathway for ozone production is thought to occur via:
O3 +hν → O(1D)+O2 …………………………..………..R1
O(1D)+H2O → 2OH …………………….……………..R2
24 Nov 2024
DMS (g)
MSA (g)
SA (g)
time_UTC
PTR
CIMS
CIMS
During DMS/MSA peak, air masses were close to the SW coast
Event 01