The Sensitivity of Aerosol Sulfate to Changes in Nitrogen Oxides and

Volatile Organic Compounds

Ariel F. Stein Department of Meteorology

The Pennsylvania State University

Sulfate

• Is the dominant inorganic constituent of PM2.5

• Reduces visibility because of its hygroscopic characteristics. Hazy summer days.

• Dry and wet deposition of sulfate: elevates the acidity levels in surface waters and soil.

• Affects regional and global climates by scattering radiation.

HOx cycle

Sinks: R O O HH O2 2

RO 2

HO 2

CO, VOC, O 3

NO, O 3

R H C O

H N O 3

NO 2

O H

h

O 3

H O2

Sources:

h

• SHOx = PHNO3 + 2 PXOOH + PPAN

• PSO4 = P H2O2 + P SO4G

• PSO4 = f([NOx] , [VOC])

• [VOC] d PSO4/d[VOC] = [NOx] d PSO4/d[NOx]

Sensitivity of SO42- to changes in

NOx and VOC abundance

))((

)(

G4SOG4SO

G4SO

Threshold3HNO

4SO

x2x1

x2k

PP

PH2O2=kH2O2[HO2]2

PSO4G=kSO4G[SO2][OH]

Streamline analysis 14 Jul 1995 1200 UTC

Ozone Concentrations

MODELS-3 description

• Community Multiscale Air Quality (CMAQ) model. 3-D Eulerian chemical transport model.

• Meteorology: Mesoscale Model 5 (MM5)

• Emissions: MODELS-3 Emissions Processing and Projection System (MEPPS).

• Chemical mechanism: RADM2

• Aerosol model: Regional Particulate Model (RPM)

• Horizontal resolution: 36 km

• Vertical layers: 15

• Domain: Northeastern USA.

N 327

1-h Peak Raw bias (ppb)a -9.7

Norm bias (%)b -7.3

Raw gross error (ppb)c 18.3

Norm gross error (%)d 18.5

Early morning (6-9 AM) Raw bias (ppb)a -1.4

Raw gross error (ppb)c 16.2

Late night (2-5 AM) Raw bias (ppb)a 6.4

Raw gross error (ppb)c 18.6

Normalized bias (%)b O3>20 ppb 5.1

O3>40 ppb -6.3

O3>60 ppb -11.8

Raw bias (ppb)a O3>20 ppb -2.6

O3>40 ppb -7.0

O3>60 ppb -11.3

Normalized gross error (%)d O3>20 ppb 33.4

O3>40 ppb 25.7

O3>60 ppb 22.5

Raw gross error (ppb)c O3>20 ppb 18.3

O3>40 ppb 18.5

O3>60 ppb 19.5

a R a w b i a s : 1

1N i

N

[ ]C ( t ) C ( t )p , i o , i

b N o r m a l i z e d r a w b i a s :

1

1N i

N [ ]C ( t ) C ( t )

C ( t )

p , i o , i

o , i

c R a w g r o s s e r r o r :

1

1N i

N

C ( t ) C ( t )p , i o , i

d N o r m a l i z e d g r o s s e r r o r :

1

1N i

N C ( t ) C ( t )

C ( t )

p , i o , i

o , i

w h e r e C p i s t h e m o d e l e d c o n c e n t r a t i o n a n dC o i s t h e m e a s u r e d c o n c e n t r a t i o n .

NOx and VOC sensitivity definition

NONOxx-sensitive locations -sensitive locations

{ [O3]35%NOx - [O3]35%VOC }< 5 ppb (~5%)

{{[H2O2]+[SO42-]}35%NOx - {[H2O2]+[SO4

2-]}35%VOC}<0.5 ppb (~5%)

________________________________________________________

VOC-sensitive locationsVOC-sensitive locations

{ [O3]35%NOx - [O3]35%VOC }> 5 ppb (~5%)

{{[H2O2]+[SO42-]}35%NOx - {[H2O2]+[SO4

2-]}35%VOC}>0.5 ppb (~5%)

Indicator / run

VOC sensitive

50th percentile

locations

95th percentile

NOx sensitive

5th percentile

locations

50th percentile

H2O2/HNO3

BASECASE 0.16 0.21 0.49 1.30

DBLSO2 0.17 0.22 0.57 1.83

DBLVOC 0.14 0.30 0.70 2.22

Sillman et al.[1997] (0.13-0.33) (0.24-0.59) (0.28-0.68) (0.73-1.58)

O3/NOz

BASECASE 8.3 9.6 12.3 25.7

DBLSO2 8.4 9.7 12.4 25.7

DBLVOC 6.8 9.6 12.7 25.8

Sillman et al.[1997] (5.8-8.6) (7.7-10.4) (7.9-11.9) (11.8-17.7)

Distribution of ozone sensitivity indicator values

Potential sulfate reduction as a function of the non-dimensional indicator.

-15

-10

-5

0

5

10

15

0.1 1 10

{[H2O2]+[SO42-]}/{[HNO3]+[NO3

-]}

{[H

2O2]

+[S

O42-

]} r

edu

ctio

n[%

]

35% NOx reductions 35% VOC reductions

Distribution of {[H2O2]+[SO42-]}/{[HNO3]+[NO3

-]} ratios for NOx- and VOC- sensitive regimes

Run 5th

percentile

VOC sensitive

50th

percentile

locations

95th

percentile

NOx sensitive

5th

percentile

locations

50th

percentile

95th

percentile

BASECASE 0.47 0.96 1.82 1.54 7.30 18.66

DBLSO2 0.30 0.89 1.37 1.73 4.76 16.86

DBLVOC 0.65 1.23 2.25 1.60 7.46 20.16

Geographical distribution of the VOC-sensitive locations for July 14 at 20:00 UTC. Shaded regions correspond to

indicator values lower than 1.

Conclusions The species ratios consistently assume

different values under NOx_sensitive and VOC_sensitive conditions.

Indicator values > 2 ==> NOx sensitivity.

Indicator values < 1.5 ==> VOC sensitivity. The value of the indicator at the transition

point between NOx_ and VOC_sensitive sulfate remains constant throughout the different runs.