Southeast US air chemistry:directions for future SEAC4RS analyses

Tropospheric Chemistry Breakout Group

DRIVING QUESTION: How do biogenic and anthropogenic emissions combine to affect atmospheric composition with implications for air quality and climate?

- How does the system respond to changing emissions?- How can the changes and responses be monitored from space?

Southeast US in summer has the highest isoprene emissions in the world…

…and rapidly decreasing NOx emissions:

Difference between 2011 and 2005 Apr-Sep OMI NO2 [Russell et al., 2012]

OMI HCHO columns, July 2006

The Southeast has a major ozone pollution problem…

…and models show very large biases in the region

HTAP model intercomparison,24-h mean ozone[Fiore et al., 2009]

EPA [2012]

Month (2001)

Ozo

ne

(pp

b)

observed

models

The Southeast also has a major PM2.5 pollution problem

Kim et al. [2015]

annualstandard

AOD has large seasonality over Southeast US …but not PM2.5

Kim et al. [2015]

Some major early results coming out of SEAC4RS

• Identification of high- and low-NOx pathways for VOC oxidation [Crounse et al.]

• Better understanding of the isoprene oxidation cascade under high- and low-NOx pathways, implications for ozone and aerosol formation [Wolfe et al., Campuzano-Jost et al., Travis et al., Yu et al., Marais et al.]

• Role of isoprene nitrates as NOx sinks and in the broader NOy budget [Crounse et al., Fisher et al.]

• Model biases in ozone over Southeast are caused by NOx biases [Travis et al.]

• AOD seasonal transition over Southeast is driven by both biogenic emissions and photochemistry [Kim et al.]

• Validation of satellite HCHO measurements [Zhu et al.]

• Oil and gas influences on VOCs [Blake et al.]

• Effects of agricultural fires on Southeast US air quality [Liu et al., Simpson et al.]

But these and other problems require more work…

Problem #1: Constructing NOx/NOy budgets for Southeast compatible with ensemble of observation constraints

• Can we get good closure for NOy measurements in SEAC4RS?• Can we reconcile measurements of NOx and of its oxidation products?• Can we reconcile NOx emission inventories with observations of NOx concentrations

and nitrate wet deposition?• What is the role of isoprene nitrates as permanent/reversible sinks for NOx?• What is the role of aerosol uptake/hydrolysis of organic nitrates?

NEI cut by 50%

wetdep nitratetoo low by 50%

NEI inventoryoverestimates NOx

Travis et al.

Isoprene emission

Problem #2: understanding VOC sources and chemistry

• Can we reconcile the observed products of the isoprene oxidation cascade with current mechanisms?

• How confidently can we constrain isoprene emissions from HCHO columns?• How do the SEAC4RS data constrain US methane sources?

Methane below 1 km in SEAC4RS

GOSAT methane, 2009-2011

Fisher et al., Yu et al.

NOx emission

Problem #3: understanding sulfate formation and properties

• Is there a missing SO2 oxidant needed to explain observed sulfate?• Why is sulfate aerosol acidic despite excess ammonia available?

- Why does ammonium aerosol show the same long-term decreases as sulfate?

f=1

f=0.5

Kim et al.

Problem #4: Understanding formation of organic aerosol

• Are different OA measurements consistent?• Can we conclude that biogenic sources dominate OA?• What are the contributions of isoprene and monoterpenes? Can we derive yields?• Can we quantify yield differences between high-NOx and low-NOx VOC oxidation

pathways?

Kim et al., Marais et al.