Nature of PM2.5 in the 

San Joaquin Valley 

Karen Magliano 

California Air Resources Board 

Technical Symposium 

April 27, 2012 

 

1
PM Characterization

2
High PM2.5 Levels Occur In Winter 

PM2.5 builds up over 

several days or 

weeks (episode)

Episodes generally 

occur during periods 

with:

• stagnation 

• cool temperatures 

• high humidity

• low mixing depths 0

5

10

15

20

25

30

35

40

1 2 3 4 5 6 7 8 9 10 11 12

PM2.5 Concentration (μg/m

3)

Month

Bakersfield-California

Monthly Average 

3
Challenge of 24-Hour Standard

Focuses on most 

severe days

Strongly influenced 

by meteorology

Impacts of episodic 

emissions such as 

residential wood 

burning

4
Monitored PM2.5 Chemical Components

Ammonium

Nitrate

67%

Ammonium

Sulfate

9%

Organic 

Carbon

16%

Elemental 

Carbon

5%

Geological

2% Elements

1%

2008-2010 Peak Day Composition

Bakersfield

5
Monitored PM2.5 Chemical Components

Ammonium 

Nitrate

51%

Ammonium 

Sulfate

6%

Organic

Carbon

33%

Elemental 

Carbon

7%

Geological

1% Elements

2%

2008-2010 Peak Day Composition

Fresno 

6
Monitored Concentrations of Key Species

0

5

10

15

20

25

30

35

Ammonium Nitrate Carbon

Bakersfield

Fresno

Concentration (μg/m

3

)

7
Ammonium Nitrate Formation 

(Excess Ammonia)

NH3 +

+

+

NOx

NOx

NH3 NOx

NH3

NH3

NH3

Atmospheric 

 Reactions

 (NH4NO3)

Ammonium

 Nitrate

Ammonium

 Nitrate

Ammonium

 Nitrate

8
Ammonium Nitrate Formation 

(NOx Control)

NH3 +

+

NOx

NOx

NH3

NH3

NH3

NH3

Atmospheric 

 Reactions

 (NH4NO3)

Ammonium

 Nitrate

Ammonium

 Nitrate

9
Measured Ammonia Much More 

Abundant than Nitric Acid

10

-10

0

10

20

30

40

50

60

-2 0 2 4 6 8 10 12 14 16 18

HNO3 Concentration (ug-N/m3)

NH3 Concentration (ug-N/m3)

1:1 Line

Angiola Monitoring Site – CRPAQS Field Study
Linkage to Modeling

11
Role of Air Quality Data in Attainment 

Demonstration

Calculate design values

Select modeling base year

Weight of Evidence

12
Design Value Calculation

Defines air quality starting point

Uses measured PM2.5 concentrations

Based on 98th percentile (generally 

between the 2nd and 8th highest value)

Calculated as 3-year average

13
Selecting Base Year For Planning

Appropriate base year considers air quality 

and meteorology

Base year with stagnant meteorology is a 

conservative approach

Attainment demonstration estimates 

change in design value between base year 

and attainment year

14
2007 Base Year

2007 meteorology one of most conducive to 

PM2.5 formation

Includes various types of meteorology 

conducive to high PM2.5 

2007 PM2.5 98th percentile concentrations 

highest in recent years

Excludes influence of 2008 wild fires

15
Design Values*

0

10

20

30

40

50

60

70

80

PM2.5 Design Value (μg/m

3)

2007 2011

* Year assigned to design value reflects last year of three year period 16
Weight of Evidence

Attainment demonstration based on weight 

of evidence approach

Collective assessment of control approach 

based on:

• air quality grid modeling

• source-receptor modeling

• observed air quality trends

• emission trends

• field/modeling studies

17
Effectiveness of Wood Burning Controls

18
Effectiveness of NOx Controls

19

0

2

4

6

8

10

12

0

100

200

300

400

500

600

2002 2003 2004 2005 2006 2007 2008 2009 2010

Ammonium Nitrate (ug/m3)

NOx Emissions (tons/day)

NOx Emissions Ammonium Nitrate (Fresno)
Future NOx Emission Trends

0

100

200

300

400

500

600

2007 2014 2019

Emissions (tons/day)

20