An odd oxygen framework for wintertime ammonium nitrate aerosol pollution in Salt Lake Valley NOx and VOC control as mitigation strategies
Carrie Womack // NOAA Earth System Research Lab and CIRES Erin McDuffie, Pete Edwards, Ale Franchin, Ann Middlebrook, Munkh Baasandorj, Steve Brown UWFPS Team UBWOS Team AQUARIUS Workshop // 26 September 2019 Wintertime PM2.5 pollution persists in the US and elsewhere
Salt Lake Valley (SLV) Cache Valley Utah Valley
San Joaquin Valley (SJV) South Coast Basin Salt Lake Valley pollution episodes occur during persistent cold air pools (PCAPs)
Typically more sensitive to these reductions
HNO (g) + NH (g) ↔ NH NO (aq) H 3 3 4 3
NOx oxidation Warmer air
In the SLV: PM2.5 = Wintertime PM2.5 ≈ Ammonium nitrate aerosol = HNO3(g)
Some of the questions driving UWFPS (2017)
• What are the chemical mechanisms that form HNO3 during PCAPs? • What control strategies would be most effective for limiting HNO3 production? Is NOx control the best strategy? “HO -NO cycle” - “Nighttime N2O5 x x HNO pNO3 3 chemistry”
O3 NO2 VOCs OH NO2 NO3 N2O5 hv
O3 HNO3 ClNO2
OVOCs HO2 NO - RO2 pNO3
Traditional More general term - Ox = O3 + NO2 Ox,total = O3 + NO2 + 2*NO3 + 3*N2O5 + ClNO2 + 1.5*(HNO3 + pNO3 ) Parameter for daytime + PANs + ANs + OH + …
photochemical O3 production Parameter for either photochemical O3 or HNO3 production During UWFPS we observed Ox,total growth during the PCAPs – an indicator of photochemical activity Clean Pollution episode Clean Day 2 of pollution episode 2000 2000
1500 1500
1000 1000 GPS altitude (mgl) GPS altitude (mgl) Inversion
500 500 layer height …and here?
0 0 Photochemistry important here 0 20 40 60 0 20 40 60 Mixing ratio (ppbv) Mixing ratio (ppbv) during UBWOS 1) Photochemistry is important even in the winter.
2) Ox,total describes both O3 (Uintah) - and pNO3 (SLV) pollution
NOx and VOC mixing ratios during PCAPs
Salt Lake Valley Uintah Basin Population: ~1,000,000 (~800 Population: ~50,000 (~2 people/km2) people/km2) Oil & natural gas wells: 0 Oil & natural gas wells: ~10,000 DSMACC modeled the O3 growth in Uintah basin – can a similar model described Ox,total in the SLV? Initialize with observations First order loss Dynamically Simple Model parameter of Atmospheric Chemical (entrainment of Complexity background air, deposition) MCM mechanisms for VOC chemistry
TUV model for photochemistry
Emissions of NOx, VOCs, HONO, HCHO
Edwards et at, Nature (2014) Using a “split” DSMACC box model accounts for chemistry occurring in the residual layer at night
Photochemistry Constant entrainment of free tropospheric air 10 am 6 pm No Day Night emissions
Residual layer No entrainment Nocturnal boundary layer
Constant surface emissions Time An Ox,total isopleth shows the NOx-VOC sensitivity of the SLV
1) Ox,total production in the SLV is NOx-saturated and VOC-limited
2) NOx reductions, in the absence of concurrent VOC reductions, will
initially increase Ox,total in - the form of pNO3 and O3.
Womack et al., GRL, 46, 4971 (2019) - O3 in Uintah and pNO3 in SLV can be explained by the HOx chain length Propagation reactions HOx chain length = HNO - Termination reactions 3 pNO3 Σ
O3 NO2 Σ VOCs OH NO2 NO3 N2O5 hv Propagation O3 TerminationHNO3 ClNO2
OVOCs HO2 NO - RO2 pNO3
Self reactions RONO2
Uintah: High VOC/NOx propagates cycle, making O3.
SLV: Low VOC/NOx quenches cycle, terminating in HNO3. What we wish we had… Unanswered questions
• More complete observations • Does VOC-limitation hold • Oxidized VOCs throughout PCAP? • Short lived radicals (HOx, NO3, • Is VOC-limitation valid etc.) throughout the winter • More complete meteorology season? • Solar radiation and photolysis • Where else is this framework rates relevant? • Vertical measurements of the boundary layer dynamics - HNO3 pNO3
O3 NO2 Summary VOCs OH NO2 NO3 N2O5 hv
O3 • Ox,total is a general parameter to describe both O3 HNO3 ClNO2
and HNO3 production. OVOCs HO2 NO - - RO2 pNO3 • O3 and pNO3 pollution are closely linked, and are endpoints of the same chemical cycle
• The NOx-VOC sensitivity isopleths also apply - to pNO3
• The SLV is both HNO3-limited, but NOx-saturated. - NOx reductions alone will initially increase pNO3 in the valley.
• This result may be a general worldwide phenomenon, as high NOx and limited radical sources are common in wintertime boundary layers. Extra slides Ale Franchin et al. Airborne and ground-based observations ACP, 18, 17259 of ammonium-nitrate-dominated aerosols (2018) in a shallow boundary layer during intense winter pollution episodes in northern Utah
Erin McDuffie et al. On the contribution of nocturnal ACP Discussions, in heterogeneous reactive nitrogen review (2019) chemistry to particulate matter formation during wintertime pollution events in Northern Utah
Alex Moravek et al: Wintertime Spatial Distribution of ACP Discussions, in Ammonia and its Emission Sources in the review (2019) Great Salt Lake Region Utah Winter Fine Particulate Study (UWFPS) January 16 – February 13, 2017
Logan (L4) Cache Twin Otter (TO) - NOx, O3, PM2.5,NH3, CH4, CO2 Valley - NOx, O3, NH3 - I- CIMS (HONO, HNO3, ClNO2, - I- CIMS (HONO, HNO3, N2O5) ClNO2, N2O5) - AMS (pNO3) - AMS (pNO3) University of Utah (UU) and Hawthorne (HW)
- NOx, O3, CO, PM2.5 - PTR-MS (aromatics, aldehydes) Salt Lake Valley
Utah Two major PCAPs observed. Valley Ammonium nitrate dominated PM2.5. Ammonia was usually in excess. 2017 was a typical winter. 50 km