Meteorological  drivers  of  surface  ozone  biases  in  the  Southeast  US  

Katie  TravisIGC8

5/3/2017Co-­‐authors:  Daniel  Jacob,  Mike  Newchurch,  Shi  Kuang,  Anne  Thompson,  

Tom  Ryerson,  Jintai Lin

Models  Cannot  Successfully  Capture  Surface  Ozone  in  the  Southeast  US

q Model  difficulties  have  been  attributed  to  uncertainties  in  NOx-­‐O3-­‐VOC  chemistry/emissions/deposition.q Recent  studies  have  similar  biases  (Canty et  al.,  2015,  Lin  et  al.,  2017).q This  is  of  concern  for  the  design  of  air  quality  regulations.

Surfa

ceMDA

8  O3

2001

Fiore  et  al,  2009

ObservationsMulti-­‐model  Mean

Jan      Feb      Mar      Apr      May    Jun    Jul      Aug      Sep      Oct      Nov      Dec

0.0 0.2 0.4 0.6 0.8NOX, ppb

0

2

4

6

8

10

12

Altitu

de, k

m

0.0 0.5 1.0 1.5HNO3+NO3

-, ppb20 40 60 80 100 120

O3, ppb

0 20 40 60 80 100ISOPN, ppt

0

2

4

6

8

10

12

Altitu

de, k

m0 200 400 600

ISOPOOH, ppt

DC8GEOS-ChemOriginal NOx

Emissions

0 50 100 150 200HPALDs, ppt

Uncertainties  in  Modeling  Ozone  in  the  Southeast  US  are  Significantly  Reduced  

thanks  to  SEAC4RSMDA8 Ozone at CASTNET sites

0 20 40 60 80 100MDA8 ozone, ppb

0.000

0.025

0.050

Prob

abilit

y Den

sity,

ppb-1 ObservationsGEOS-ChemReduced NOx

q Reduced  MDA8  ozone  by  ~10ppb.  Successfully  captured  SEAC4RS  ozone  production  efficiency  of  ~17  (unscaled  =  15).q Largely  due  to  reduction  (~50%)  to  EPA  NEI  NOx  inventory  confirmed  by  previous  and  subsequent  studies.q Observations  of  nitrate  wet  deposition  fluxes  indicate  that  the  EPA  NEI  inventory  may  be  biased  across  the  entire  US.

Unique Tracers of Isoprene Oxidation

MDA8 Ozone at CASTNET Sites

Travis  et  al.  (2016)PI.  P.  Wennberg

*See  Fisher  et  al.,  2016

0.0 0.2 0.4 0.6 0.8NOX, ppb

0

2

4

6

8

10

12

Altit

ude,

km

0.0 0.5 1.0 1.5HNO3+NO3

-, ppb20 40 60 80 100 120

O3, ppb

0 20 40 60 80 100ISOPN, ppt

0

2

4

6

8

10

12

Altit

ude,

km

0 200 400 600ISOPOOH, ppt

DC8GEOS-ChemOriginal NOx

Emissions

0 50 100 150 200HPALDs, ppt

O3, NOx, and HNO3

PI.  J.  Dibb

PI.  T.  RyersonPI.  T.  

Ryerson

ObservationsModelOriginal  NOx

q Surface  O3 remains  biased  by  8  ppb.q Model misses low tail below 25 ppb (6% of obs).q Just 1 exceedance of 70 ppb in 2013 (24 in 2011).

q Implied  gradient  suggests  need  for  a  surface  correction  from  the  lowest  model  grid-­‐point  (~60m)  to  the  measurement  altitude  (~10m).

We  have  a  successful  NOx simulation  in  the  Southeast  US  but  a  bias  in  surface  O3

PI  T.  Ryerson

Ozone, ppb

Afternoon ozone at 0.4-1.0 km altitude

0 20 40 60 80 100 0.000

0.025

0.050

Pro

babi

lity D

ensit

y, p

pb-1

Observation

Model52 + 10 ppb

50 + 11 ppb

nn=370

_

_

_

20 40 60 80 100MDA8 ozone, ppb

Observation 40 + 9 ppb

MDA8 Ozone at CASTNET sites

_Model48 + 9 ppb

Ozone, ppb

Afternoon ozone at 0.4-1.0 km altitude

0 20 40 60 80 100 0.000

0.025

0.050 P

roba

bility

Den

sity,

ppb

-1Observation

Model52 + 10 ppb

50 + 11 ppb

nn=370

_

_

_

20 40 60 80 100MDA8 ozone, ppb

Observation

Model (10 m)45 + 8 ppb

40 + 9 ppb

MDA8 Ozone at CASTNET sites

_

_

Model (58 m)48 + 9 ppb

q We recalculate RA from the first model grid point to 10m to obtain the model value at this altitude.

q Correction is 3 ppb in the Southeast US.

q Correction is larger when the atmosphere is more stable.

Surface  Correction  is  Significant  for  MDA8  Ozone

Height  of  the  first  model  grid-­‐point

Brasseur  and  Jacob  (2016)

August-­‐September  2013  was  a  cool  and  wet  year,  but  not  an  outlier

qThe relatively low surface ozone measured at CASTNET sites in August-September 2013 reflects lower-than-average but not anomalous conditions. qAbout 30% wetter, 1oC cooler

qWet and cool also means cloudier than average à 2013 had approximately 50% greater low-cloud than 2011.

qHow do these conditions challenge model skill in capturing MDA8 ozone?

Weak  model  response  to  cloudy/rainy  conditions  cause  model  bias

q Rainy conditions explain the low tail of MDA8. Model failure could be due to stratification from evaporative cooling.q In the Southeast US, GEOS-Chem low cloud is underestimated by ~70% and rain is underestimated by ~30%.q Model response to cloud cover is ~50% of observed response. Correcting for missing cloud cover does not improve bias.

Observation

0 20 40 60 80 100MDA8 ozone, ppb

0.00

0.05

0.10Pr

obab

ility,

ppb

-1Model

0 20 40 60 80 100MDA8 ozone, ppb

Clear: 45 + 9 (15%)Low-Cloud: 38 + 8 (29%)

Rain: 34 + 9 (17%)

45 + 8 (62%) 41 + 3 ( 4%)41 + 7 ( 6%)

Model  compares  well  with  Southeast  US  ozonesonde  from  3-­‐12  km

Launch Date

02

4

6

8

10

12

Altit

ude,

km

155085120

02

4

6

8

10

12

Launch Date

2

4

6

8

10

12

Altit

ude,

km

GEOS-Chem

2

4

6

8

10

12

Launch Date

0.00.5

1.0

1.5

2.0

2.5

3.0

Altit

ude,

km

Ozonesonde

0.00.5

1.0

1.5

2.0

2.5

3.0

0.00.5

1.0

1.5

2.0

2.5

3.0

Altit

ude,

km

GEOS-Chem

1530456075

0.00.5

1.0

1.5

2.0

2.5

3.0

August September

Vertical profiles of ozone over Huntsville, Alabama in Aug-Sep 2013

Ozonesonde

Lowest 3km

Model CloudASOS Cloud

PRISM PrecipModel Precip

8 9 10 12 13 15 17 19 20 21 24 26 27 28 29 30 31 2 4 6 7 10 12 14 16 18 2016 2322 21August SeptemberCloudy Clear Rainy14 19 1 6 4 0 0 0 2 20 2 6 9 0 0 0 0 0 0 5 32 0 0 0 4 0 0 0 0 0 506 3 3 2 2 1 1 1 2 8 5 3 1 0 0 0 0 0 1 1 5 0 0 0 1 4 0 0 0 0 47

0.5 0.4 0.5 0.0 0.5 0.8 1.0 1.0 0.5 0.4 0.4 0.4 0.0 0.3 0.3 0.4 0.4 0.3 0.5 0.4 0.3 0.0 0.0 0.4 0.3 0.4 0.0 0.0 0.3 0.1 0.70.0 0.1 0.2 0.0 0.2 0.3 0.5 0.3 0.1 0.3 0.4 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.3 0.0 0.3

8 9 10 12 13 15 17 19 20 21 24 26 27 28 29 30 31 2 4 6 7 10 12 14 16 18 2016 2322 21

Ozone, ppb

Ozone, ppb

Bias  from  3-­‐12  km  is  1  ± 12  ppb  

2468

1012

Altit

ude,

km

0 20 40 60 80 100

Huntsville, Alabama

SEACIONSGEOS-Chem

O3, ppb

Observed  gradient  may  be  strongest  on  cloudy  days,  and  is  not  captured  by  the  model

Launch Date

02

4

6

8

10

12

Altit

ude,

km

155085120

02

4

6

8

10

12

Launch Date

2

4

6

8

10

12

Altit

ude,

km

GEOS-Chem

2

4

6

8

10

12

Launch Date

0.00.5

1.0

1.5

2.0

2.5

3.0

Altit

ude,

km

Ozonesonde

0.00.5

1.0

1.5

2.0

2.5

3.0

0.00.5

1.0

1.5

2.0

2.5

3.0

Altit

ude,

km

GEOS-Chem

1530456075

0.00.5

1.0

1.5

2.0

2.5

3.0

August September

Vertical profiles of ozone over Huntsville, Alabama in Aug-Sep 2013

Ozonesonde

Lowest 3km

Model CloudASOS Cloud

PRISM PrecipModel Precip

8 9 10 12 13 15 17 19 20 21 24 26 27 28 29 30 31 2 4 6 7 10 12 14 16 18 2016 22 21August SeptemberCloudy Clear Rainy14 19 1 6 4 0 0 0 2 20 2 6 9 0 0 0 0 0 0 5 32 0 0 0 4 0 0 0 0 0 506 3 3 2 2 1 1 1 2 8 5 3 1 0 0 0 0 0 1 1 5 0 0 0 1 4 0 0 0 0 47

0.5 0.4 0.5 0.0 0.5 0.8 1.0 1.0 0.5 0.4 0.4 0.4 0.0 0.3 0.3 0.4 0.4 0.3 0.5 0.4 0.3 0.0 0.0 0.4 0.3 0.4 0.0 0.0 0.3 0.1 0.70.0 0.1 0.2 0.0 0.2 0.3 0.5 0.3 0.1 0.3 0.4 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.3 0.0 0.3

8 9 10 12 13 15 17 19 20 21 24 26 27 28 29 30 31 2 4 6 7 10 12 14 16 18 2016 2322 21

Ozone, ppb

Ozone, ppb

2340 45 50 55 60

Ozone, ppb

0.0

0.5

1.0

1.5

2.0

Altit

ude,

km

Huntsville, Alabama

SEACIONSGEOS-Chem

q Cloudy  observations  show  the  largest  gradient  à 8  + 6  ppb.  Model  cloud  profiles  are  flat.q Increasing  the  sink  of  ozone  would  not  change  the  model  gradient.  Slower  mixing  improves  the  profile.q Slower  entrainment,  ozone  production,  or  a  surface  sink  would  still  be  required  to  reconcile  model  bias.

Mean  Profile

Conclusions

• Uncertainty  in  modeling  surface  ozone  in  the  Southeast  US  is  significantly  improved  due  to  better  constraints  on  isoprene  chemistry  and  NOx budget.• EPA  NOx inventory  may  be  overestimated  by  as  much  as  50%.• Model  is  still  biased  by  ~8  ppb  against  surface  observations.• The  correction  for  the  ozone  gradient  below  the  lowest  model  grid-­‐point  is  significant  (3  ppb)  and  should  be  applied  in  future  studies.• Rainy  conditions  explain  the  larger  model  bias  at  low  values  of  MDA8  ozone.• The  weak  model  response  to  low-­‐cloud  cover  (and  missing  model  low-­‐cloud)  explains  the  remaining  model  bias.