­Ozone and organic nitrates over the eastern US:sensitivity to isoprene chemistry

Jingqiu Mao (NOAA GFDL), Fabien Paulot (Harvard), Daniel Jacob (Harvard), Ronald Cohen (UC Berkeley), John Crounse (Caltech), Paul Wennberg (Caltech), Christoph Keller (Harvard), Rynda Hudman (EPA), Michael Barkley(U Leicester), Larry Horowitz (NOAA GFDL)

Summertime ozone over eastern US is a classic problem for most models

(Fiore et al., 2009, JGR)

Multimodel mean

Obs from CASTNET surface sites

Northeast US

Southeast US

Multimodel mean

Obs from CASTNET surface sites

We didn’t have this problem during ICARTT!

(Hudman et al., 2007, JGR)

DC-8 ozone

WP-3D ozone

NO

12

34

OH

11.7%

O

MVK

First generation isoprene nitrates

O

MACRH

O

H

HCHO

88%Organic peroxides

OHOO

OO

OH

-hydroxyl peroxy radicaland isomers

-hydroxyl peroxy radicaland isomers

79% 21%

HO2 1,6-H shif t isomerization

4.7%

7.3%

12%26% 40% 66%

HOOO

HPALDs

hvOH100%

100%

C2 and C3 carbonyl compounds

ISOPO2 ISOPO2

Switching to Fabien’s isoprene chemistry

(1) smaller yield of isopreneNitrate (IN)

(2) IN is not a terminal sink!

OH

ONO2

ISOPN (1,4)

OHONO2

ISOPN (1,2)

OHONO2

ISOPN (4,3)

ONO2

OH

ISOPN (4,1)

O

OH

ONO2

methylvinylketone nitrate (MVKN)

O2NO O

ethanal nitrate(ETHLN)

O2NO

O

propanone nitrate(PROPNN)

O

methacrolein nitrate(MACRN)

ONO2

OH

OH/O2

OH

ONO2

OHOO

NO

OH

ONO2

OHO

OHONO2

OHOO

NO

OHONO2

OHO

ONO2

OH

OHOO

NO

ONO2

OH

OHO

OHONO2

OHOO

NO

OHONO2

OHO

OH/O2OH/O2OH/O2

First generation of isoprene nitrates degraded to second generation nitrates!

NOx recycling efficiency is 55%!

Ozone bias is about +5 ppb in both boundary layer and free troposphere!

ObsStd chem (v8-2-3)Paulot isoprene chem

Surface

500 hPa

A few more updates (impact on July afternoon ozone of 2004)

(Mao et al., ACP 2013) Implemented by Christoph Keller

(Parrella et al., ACP 2012)

We are now in good shape...

Ozone in the boundary layer during ICARTTObservations Model

Obs vs. ModelImproved O3-CO correlations due to:1. Recycling of NOx

from isoprene nitrates

2. HO2 uptake (lower OH and increase NOx lifetime).

Mean vertical profiles during ICARTT

O3 has no bias in boundary layer and free troposphere.HCHO provides good constraint on isoprene emissions.

ObservationsModel (this work)

Total organic nitrates excluding peroxyacylnitrates (∑ANs)

Model well reproduced ∑ANs.

∑ ANs is dominated by secondary organic nitrates.

∑ANs vs. HCHO ∑ANs vs. O3

Model well reproduced ∑ANs vs. HCHO and ∑ANs vs. O3 correlations.

These correlations cannot be reproduced by a fast isomerization channel of ISOPO2.

Vertical profiles Speciation of ∑ANs

NOy budget in eastern U.S. boundary layer for July 2004

Species Emission Chemical(P-L)

Dry Deposition

Wet Deposition

Net Export

NOx 386 -337 44 ------ 5PANs   24 13 ------ 11∑ANs           ANs   18 7.4 3.6 7 R4N2   10 0.5 ------- 10HNO3   277 180 110 -3

Export of ∑ANs > Export of PANs

Surface ozone response to isoprene emissions

New chemistry

Current anthro NOx emissions

Reduce current anthro NOx emissions by 50%

NOx emissions↓

Sensitivity of ozone to isoprene emissions ↓

New chemistry

V8-02-03 chemistry

Current anthro NOx emissions

Reduce current anthro NOx emissions by 50%

Isoprene↑NOx ↓OH ↓O3 ↓ due to O3+ISOP

Surface ozone response to isoprene emissions

Extra slides

Old diurnal cycle for NOx emissions New diurnal cycle for NOx emissions

In the old diurnal cycle, very little NOx is emitted in the late afternoon.

Diurnal cycle in southeast US in summer Red: old version Black: new version

Consequently NOx in new version is higher than in old version by a factor of 2.