APPENDIX D – 

Emissions Inventory Evaluation by Sonoma Technology, Inc. 
A Top-Down Emissions Inventory 

Evaluation for the Upper Midwest 

Final Report 

Prepared for 

National Renewable Energy Laboratory 

Golden, CO 

May 2011

Cover graphic illustrates the locations of monitoring sites included in the top-down emissions inventory evaluation. 

See Section 1 for more information.

A Top-Down Emissions Inventory 

Evaluation for the Upper Midwest 

Final Report 

NREL Contract # AFA-9-99135-0 

STI-909028-3808-FR 

Prepared by 

Stephen B. Reid 

Erin K. Pollard 

Yuan Du 

John C. Stilley 

Sonoma Technology, Inc. 

1455 N. McDowell Blvd., Suite D 

Petaluma, CA 94954-6503 

Ph 707.665.9900 | F 707.665.9800 

sonomatech.com 

Prepared for 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, CO 80401-3393 

May 31, 2011 

Upper Midwest Emissions Inventory Evaluation Acknowledgments 

Acknowledgments 

Funding for this project was provided by the U.S. Department of Energy Office of 

Vehicle Technologies under the direction of Dr. James Eberhardt, Chief Scientist. The authors 

acknowledge the assistance of Mark Janssen and Mike Koerber of the Lake Michigan Air 

Directors Consortium (LADCO), who provided access to the emissions inventory data that was 

used for the analyses described in this report. We also acknowledge Doug Lawson of the 

National Renewable Energy Laboratory (NREL), who managed the project for NREL and 

provided technical guidance and support throughout the project. 

Upper Midwest Emissions Inventory Evaluation Table of Contents 

iii

Table of Contents 

Section Page

List of Figures................................................................................................................................. v 

List of Tables ...............................................................................................................................viii 

Glossary ......................................................................................................................................... ix 

1. Introduction ........................................................................................................................ 1-1 

1.1 Background............................................................................................................... 1-1 

1.2 Overview of Technical Approach............................................................................. 1-2 

1.2.1 Site Selection and Data Processing .............................................................. 1-2 

1.2.2 Comparison of Ambient- and Emissions Inventory-Derived Criteria 

Pollutant Ratios ............................................................................................ 1-4 

1.2.3 Comparison of Ambient- and Emissions Inventory-Derived 

Hydrocarbon Compositions.......................................................................... 1-6 

1.3 Uncertainty Issues..................................................................................................... 1-6 

1.3.1 Emissions Inventory Uncertainties............................................................... 1-6 

1.3.2 Ambient Measurement Uncertainties........................................................... 1-7 

1.3.3 Uncertainties Associated with the Comparisons .......................................... 1-7 

1.4 Summary of Results.................................................................................................. 1-8 

2. Data Acquisition and Processing........................................................................................ 2-1 

2.1 Ambient Monitoring Data......................................................................................... 2-1 

2.1.1 Ambient Data Acquisition............................................................................ 2-1 

2.1.2 Ambient Data Validation.............................................................................. 2-2 

2.1.3 Ambient Site Characterization ..................................................................... 2-5 

2.1.4 Ambient Concentration Data...................................................................... 2-11 

2.1.5 Ambient Data Screening ............................................................................ 2-24 

2.2 Emissions Inventory Data....................................................................................... 2-24 

2.2.1 Emissions Data Acquisition and Processing .............................................. 2-24 

2.2.2 Emissions Data Characterizations by Site.................................................. 2-27 

3. Pollutant Ratio Comparison Results .................................................................................. 3-1 

3.1 TNMOC/NOx Ratio Comparisons............................................................................ 3-1 

3.1.1 Ratio Comparison Results for Chicago-Jardine ........................................... 3-2 

3.1.2 Ratio Comparison Results for Chicago-Northbrook .................................... 3-3 

3.1.3 Ratio Comparison Results for Gary ............................................................. 3-5 

3.1.4 Ratio Comparison Results for Detroit-East 7 Mile ...................................... 3-5 

3.1.5 Ratio Comparison Results for Milwaukee ................................................... 3-6 

3.2 CO/NOx Ratio Comparisons..................................................................................... 3-8 

3.2.1 Ratio Comparison Results for Chicago-Mannheim ..................................... 3-9 

3.2.2 Ratio Comparison Results for Chicago-Franklin ....................................... 3-11 

3.2.3 Ratio Comparison Results for Chicago-Northbrook .................................. 3-13 

3.2.4 Ratio Comparison Results for Detroit-Linwood ........................................ 3-14 

3.2.5 Ratio Comparison Results for Milwaukee ................................................. 3-15
Upper Midwest Emissions Inventory Evaluation Table of Contents 

iv

Section Page

4. Hydrocarbon Composition Comparison Results................................................................ 4-1 

4.1 Relative Hydrocarbon Composition Comparisons ................................................... 4-1 

4.2 Hydrocarbon Reactivity Comparisons...................................................................... 4-4 

5. Findings and Recommendations ........................................................................................ 5-1 

6. References .......................................................................................................................... 6-1 

Appendix A: Chemical Species Cross-Reference List .............................................................. A-1 

Appendix B: Monitoring Site Photographs.................................................................................B-1 

Appendix C: Diurnal Concentration Plots for 2008 and 2009....................................................C-1 

Appendix D: Additional Comparisons of Pollutant Ratios........................................................ D-1 

Appendix E: Additional Comparisons of Hydrocarbon Compositions ......................................E-1 
Upper Midwest Emissions Inventory Evaluation List of Figures 

v

List of Figures 

Figure Page 

1-1. Locations of monitoring sites included in the top-down emissions inventory 

evaluation......................................................................................................................... 1-3 

1-2. Example of a full extent grid analysis zone, showing the spatial configuration of 

grid cells for which ambient- and emissions inventory-derived ratio comparisons 

were calculated................................................................................................................. 1-5 

2-1. Time series of propane and ethane concentrations (ppbC) at Gary, IN........................... 2-3 

2-2. Time series of CO concentrations (ppb) for Linwood site in Detroit, MI ....................... 2-4 

2-3. Yearly variations in summer weekday TNMOC concentrations (ppbC) at the 

Northbrook site in Chicago, IL. ....................................................................................... 2-5 

2-4. Image of the area around the Jardine and Franklin sites in Chicago ............................... 2-6 

2-5. Image of the area around the Northbrook site in Chicago............................................... 2-7 

2-6. Image of the area around the Mannheim site in Chicago ................................................ 2-8 

2-7. Image of the area around the Gary site ............................................................................ 2-9 

2-8. Image of the area around the East 7 Mile and Linwood sites in Detroit ....................... 2-10 

2-9. Image of the area around the Milwaukee site ................................................................ 2-11 

2-10. Interpretation of notched box whisker plots produced by SYSTAT ............................. 2-15 

2-11. Hourly TNMOC and NOx concentrations for the Chicago-Jardine site for summer 

weekdays, Saturdays and Sundays, 2004–2006............................................................. 2-16 

2-12. Hourly TNMOC and NOx concentrations for the Chicago-Northbrook site for 

summer weekdays, Saturdays, and Sundays, 2004–2006.............................................. 2-17 

2-13. Hourly TNMOC and NOx concentrations for the Gary site for summer weekdays, 

Saturdays and Sundays, 2004–2006 .............................................................................. 2-18 

2-14. Hourly TNMOC and NOx concentrations for the Detroit-East 7 Mile site for 

summer weekdays, Saturdays, and Sundays, 2004–2006.............................................. 2-19 

2-15. Hourly TNMOC, NOx, and CO concentrations for the Milwaukee site for summer 

weekdays, Saturdays, and Sundays 2004–2006............................................................. 2-20 
Upper Midwest Emissions Inventory Evaluation List of Figures 

vi

Figure Page

2-16. Hourly CO and NOx concentrations for the Chicago-Mannheim site for summer 

weekdays, Saturdays, and Sundays, 2004–2006............................................................ 2-21 

2-17. Hourly CO and NOx concentrations for the Chicago-Franklin site for summer 

weekdays, Saturdays, and Sundays (right), 2004–2006 ................................................ 2-22 

2-18. Hourly CO and NOx concentrations for the Detroit-Linwood site for summer 

weekdays, Saturdays, and Sundays, 2004–2006............................................................ 2-23 

2-19. Emissions grid domains for the LADCO 2005 Base M inventories.............................. 2-25 

2-20. January weekday emissions by source sector for the grid analysis zone around each 

monitoring site for hours 0600 to 0900 ......................................................................... 2-30 

2-21. July weekday emissions by source sector for the grid analysis zone around each 

monitoring site for hours 0600 to 0900 ......................................................................... 2-31 

2-22. January and July weekday on-road mobile source emissions for the grid analysis 

zone around each monitoring site for hour 0600-0900.................................................. 2-32 

2-23. Spatial distributions of NOx emissions from on-road mobile sources in Cook 

County for LADCO’s 2005 and 2008 inventories......................................................... 2-33 

2-24. Day of week emissions profiles for on-road mobile sources......................................... 2-33 

3-1. TNMOC/NOx ratios by wind quadrant and day of week for the Jardine site, 

2004-2006 ........................................................................................................................ 3-3 

3-2. TNMOC/NOx ratios by wind quadrant and day of week for the Northbrook site, 

2004–2006........................................................................................................................ 3-3 

3-3. TNMOC/NOx ratios by wind quadrant and day of week for the Northbrook site, 

2008.................................................................................................................................. 3-4 

3-4. TNMOC/NOx ratios by wind quadrant and day of week for the Gary site, 

2004-2006 ........................................................................................................................ 3-5 

3-5. TNMOC/NOx ratios by wind quadrant and day of week for the East 7 Mile site, 

2004–2006........................................................................................................................ 3-6 

3-6. TNMOC/NOx ratios by wind quadrant and day of week for the Milwaukee site, 

2004–2006........................................................................................................................ 3-7 

3-7. TNMOC/NOx ratios by wind quadrant and day of week for the Milwaukee site, 

2008.................................................................................................................................. 3-7 
Upper Midwest Emissions Inventory Evaluation List of Figures 

vii

Figure Page

3-8. CO/NOx ratios by season, wind quadrant, and day of week for the ChicagoMannheim site, 2004–2006............................................................................................ 3-10 

3-9. CO/NOx ratios by season, wind quadrant, and day of week for the ChicagoMannheim site, 2008...................................................................................................... 3-11 

3-10. CO/NOx ratios by season and by day of week for the Chicago-Franklin site, 

2004-2006. ..................................................................................................................... 3-12 

3-11. CO/NOx ratios by season and by day of week for the Chicago-Franklin site, 2008...... 3-12 

3-12. CO/NOx ratios by season, wind quadrant, and day of week for the ChicagoNorthbrook site, 2008. ................................................................................................... 3-14 

3-13. CO/NOx ratios by season and by day of week for the Detroit-Linwood site, 

2004-2006. ..................................................................................................................... 3-15 

3-14. CO/NOx ratios by season, wind quadrant, and day of week for the Milwaukee site, 

2004–2006...................................................................................................................... 3-16 

4-1. Comparison of 0600–0900 ambient- and emissions inventory-derived TNMOC 

compositions for the Chicago-Jardine site....................................................................... 4-2 

4-2. Comparison of 0600–0900 ambient- and emissions inventory-derived TNMOC 

compositions for the Chicago-Northbrook site................................................................ 4-2 

4-3. Comparison of 0600–0900 ambient- and emissions inventory-derived TNMOC 

compositions for the Gary site. ........................................................................................ 4-3 

4-4. Comparison of 0600–0900 ambient- and emissions inventory-derived TNMOC 

compositions for the Detroit-East 7 Mile site.................................................................. 4-3 

4-5. Comparison of 0600–0900 ambient- and emissions inventory-derived TNMOC 

compositions for the Milwaukee site. .............................................................................. 4-4 
Upper Midwest Emissions Inventory Evaluation List of Tables 

viii

List of Tables 

Table Page

1-1. Monitoring sites included in the top-down emissions inventory evaluation ................... 1-3 

1-2. Dimensions of the full grid analysis zone around each monitoring site of interest......... 1-5 

2-1. Hourly data available at individual monitoring sites ....................................................... 2-2 

2-2. Mean summer TNMOC and NOx concentrations.......................................................... 2-12 

2-3. Mean summer (June–August) CO and NOx concentrations. ......................................... 2-13 

2-4. Mean winter (December–February) CO and NOx concentrations................................. 2-14 

2-5. LADCO emissions inventory files for January 14, 2005............................................... 2-25 

2-6. Summary of summer (July) VOC and NOx emissions for hours 0600 to 0900 for 

the grid analysis zone around each monitoring site analyzed........................................ 2-28 

2-7. Summary of summer (July) CO and NOx emissions for hours 0600 to 0900 for the 

grid analysis zone around each monitoring site analyzed.............................................. 2-29 

2-8. Summary of winter (January) CO and NOx emissions for hours 0600 to 0900 for 

the grid analysis zone around each monitoring site analyzed........................................ 2-29 

3-1. TNMOC/NOx ratios by site for the hours 0600 to 0900 (emission ratios for full grid 

extent around each site; ambient ratios for 2005 based on 2004–2006 data). ................. 3-2 

3-2. CO/NOx ratios by site (emission ratios for full grid extent around each site; ambient 

ratios for 2005 based on 2004–2006 data)....................................................................... 3-9 

4-1. Reactivity values by site, day of week, month, and season. ............................................ 4-5 

4-2. Reactivity values by wind quadrant (all summer months included)................................ 4-6 
Upper Midwest Emissions Inventory Evaluation Glossary 

ix

Glossary 

Term Definition 

AQS Air Quality System – the U.S. Environmental Protection Agency’s repository of 

ambient air quality data 

CAMx Comprehensive Air Quality Model with extensions 

CO Carbon monoxide 

CONCEPT Consolidated Community Emissions Processing Tool 

DRI Desert Research Institute 

EGU Electrical generating units 

EPA Environmental Protection Agency 

HC Hydrocarbon 

LADCO Lake Michigan Air Directors Consortium 

MIR Maximum incremental reactivity 

NO Nitric oxide 

NOx Oxides of nitrogen 

NREL National Renewable Energy Laboratory 

PAMS Photochemical Assessment Monitoring Stations 

PAMSHC Hydrocarbon species measured at Photochemical Assessment Monitoring Stations

PAR Paraffin carbon bond 

PMF Positive matrix factorization 

ppb Parts per billion 

ppbC Parts per billion carbon 

TNMOC Total nonmethane organic compounds 

VOC Volatile organic compounds 

VOCDat Volatile Organic Compound Data Validation and Analysis Software 

 

Upper Midwest Emissions Inventory Evaluation Introduction 

1-1

1. Introduction 

The Health Impacts Program of the National Renewable Energy Laboratory (NREL) is 

responsible for quantifying the effects of new vehicle technologies and fuels on air quality and 

human health and, as such, is interested in the quality of on-road mobile source emissions 

inventories. Under funding from the U.S. Department of Energy Office of Vehicle Technologies 

through NREL, Sonoma Technology, Inc. (STI) performed a top-down evaluation of the 2005 

and 2008 emissions inventories that the Lake Michigan Air Directors Consortium (LADCO) is 

using to conduct regional air quality modeling in the Upper Midwest, with a special focus on the 

on-road mobile source component of the inventories. 

Several techniques can be used to evaluate the accuracy and representativeness of any 

emissions inventory that is intended for use in air quality modeling: “common sense” review of 

the data; bottom-up evaluations that start with emissions activity data to estimate corresponding 

emissions; and top-down evaluations that compare emissions estimates to ambient air quality 

data or use ambient data to estimate emissions profiles. As a top-down emissions inventory 

evaluation, the work described in this report was focused on comparing the LADCO emissions 

inventories to ambient monitoring data collected at four urban areas in the region of interest: 

Chicago, Illinois; Milwaukee, Wisconsin; Gary, Indiana; and Detroit, Michigan. The goals of 

the project were to identify areas of agreement and differences between the ambient data and 

emissions inventories, to identify areas of the emissions inventories that may need improvement, 

and to demonstrate the usefulness of top-down emissions inventory evaluation techniques. 

The basic approaches used to perform the top-down evaluation followed methods 

developed by Fujita et al. (1992) and outlined in a 2005 Desert Research Institute (DRI) report 

(Desert Research Institute, 2005) and elsewhere (Chinkin and Reid, 2006; Roberts et al., 2004). 

The approaches include comparisons of pollutant ratios (e.g., total non-methane organic carbon 

[TNMOC]/oxides of nitrogen [NOx] and carbon monoxide [CO]/NOx) that are derived from 

ambient data (ambient-derived) with those derived from the emissions inventory (emissions 

inventory-derived), as well as comparisons of ambient- and emissions inventory-derived relative 

hydrocarbon compositions. Results of these comparisons were used to address the reliability and 

completeness of, and to make recommendations for improving, the LADCO emissions 

inventories. 

1.1 Background 

The objective of this project is to evaluate the hourly emissions inventory for different 

urban areas in the Upper Midwest, using ambient data collected from 2004 through 2006 and 

2008 through 2010. This work focuses on assessing recent (2005 and 2008) emissions estimates 

and how well they represent real-world pollutant concentrations in the areas of interest.1

 

Ambient-derived and emissions inventory-derived primary pollutant ratios (TNMOC/NOx and 

CO/NOx) and relative hydrocarbon compositions were spatially and temporally compared for 

ambient site locations in Chicago, Milwaukee, Gary, and Detroit. In addition, analyses were 

 

1

 The initial focus of the project was comparing 2004–2006 ambient data with 2005 emissions estimates; however, 

analyses of 2008 ambient and emissions data were included once 2008 emissions inventories became available. 
Upper Midwest Emissions Inventory Evaluation Introduction 

1-2

performed on 2009-2010 ambient data to evaluate ambient measurement trends during the 

current economic downturn. 

Comparison of ambient- and emissions inventory-derived primary pollutant ratios has 

proven to be a useful tool for assessing and then improving emissions estimates. However, these 

types of comparisons are confounded by the fact that ambient concentrations are influenced not 

only by fresh pollutants emitted in the vicinity of a monitor, but also by aged pollutants 

transported from sources farther away and chemical reactions that may have occurred after the 

pollutants were emitted. The influence of these effects on comparisons can be minimized (but 

not eliminated) by selecting ambient data collected at times when emission rates are high and 

chemical reaction rates are low. Morning sampling periods offer the best potential to minimize 

the effects of pollutant transport and other influences in the ambient/emissions inventory 

comparisons. During early morning hours, because of low mixing heights, emissions from 

elevated sources may be injected above the mixed layer and may not affect surface-level ambient 

concentrations. Pollutant ratios were calculated with and without elevated sources to evaluate 

the potential effects of this phenomenon. 

1.2 Overview of Technical Approach 

STI used techniques outlined by DRI (Desert Research Institute, 2005) to perform this 

top-down emissions inventory evaluation. These techniques have been previously applied by 

STI to emissions inventories for several other geographic areas, including central California 

(Chinkin and Reid, 2006), Southern California (Fujita et al., 1992; Chinkin et al., 2005), and 

Houston, Texas (Roberts et al., 2004). The technical approach for this top-down emissions 

inventory reconciliation was divided into three elements: 

1. Site selection and data processing; 

2. Comparison of emissions inventory and ambient criteria pollutant ratios; and 

3. Comparison of emissions inventory and ambient relative hydrocarbon compositions. 

The approach used to carry out each work element is described in the following sections. 

1.2.1 Site Selection and Data Processing 

To support a top-down emissions inventory evaluation for the cities of Chicago, 

Milwaukee, Gary, and Detroit, STI acquired available air quality and meteorological data from 

the U.S. Environmental Protection Agency’s (EPA) Air Quality System (AQS) for eight 

monitoring sites, as shown in Table 1-1 and Figure 1-1. To effectively evaluate on-road mobile 

source emissions estimates, an effort was made to focus on monitoring sites that are likely to be 

impacted by fresh mobile source emissions. However, some of the sites included in these 

analyses were in the vicinity of other emissions sources, including non-road mobile sources (e.g., 

the Jardine and Mannheim sites in Chicago) and industrial sources (e.g., the Gary site), as 

described in Section 2.2. Hourly data for the years 2004–2006 and 2008–20102

 were acquired 

 

2

 It should be noted that 2008–2010 data were not available for several sites that reported 2004–2006 data, as 

documented in Section 2.1.1. 
Upper Midwest Emissions Inventory Evaluation Introduction 

1-3

from AQS for summer (June-August) and winter (December-February) months, and data were 

validated following established protocols. 

Table 1-1. Monitoring sites included in the top-down emissions inventory evaluation.

Site Name AQS Code Site Typea Latitude Longitude

Chicago, IL – Jardine 17-031-0072 PAMS II 41.8958 -87.6077

Chicago, IL – Northbrook 17-031-4201 PAMS 42.1400 -87.7992

Chicago, IL – Franklin 17-031-0063 SLAMS/Other 41.8770 -87.6343

Chicago, IL – Mannheim 17-031-3103 SLAMS/Other 41.9652 -87.8763

Gary, IN 18-089-0022 PAMS II 41.6067 -87.3047

Detroit, MI – E7Mile 26-163-0019 SLAMS/Other 42.4308 -83.0001

Detroit, MI – Linwood 26-163-0016 SLAMS/Other 42.3578 -83.0960

Milwaukee, WI 55-079-0026 PAMS II 43.0611 -87.9125

a PAMS = Photochemical Assessment Monitoring Stations; SLAMS = State/Local Air Monitoring Stations. 

Figure 1-1. Locations of monitoring sites included in the top-down emissions inventory 

evaluation. 
Upper Midwest Emissions Inventory Evaluation Introduction 

1-4

STI also acquired 2005 Base M and 2008 Base B/C emissions inventory data files and 

supporting files (e.g., speciation profile libraries) for area, point, non-road mobile, on-road 

mobile, and biogenic sources from LADCO. In general, LADCO provided hourly, gridded 

criteria pollutant (e.g., volatile organic compounds [VOC], NOx, and CO) emissions data 

representing an average weekday, Saturday, and Sunday for each month of 2005 and 2008.3

 

Emission file formats varied by source sector4, so to prepare the emissions data for use in 

subsequent analyses, STI converted all data files to a common comma-separated-values (CSV) 

format and extracted data records for the grid cells included in the grid analysis zones around 

each monitoring site of interest (see Section 1.2.2 for a description of how grid analysis zones 

were defined for each site). In addition, STI speciated anthropogenic VOC emissions using 

speciation profiles and cross-reference files provided by LADCO, then matched individual 

chemical species in the speciated inventories to those species measured in the ambient data (i.e., 

PAMS hydrocarbons). The compounds reported in the emissions inventory that were not 

measurable in the ambient samples were excluded from the analysis. Finally, STI converted the 

speciated inventories from mass to molar units to place the emissions and ambient data on a 

common basis. 

1.2.2 Comparison of Ambient- and Emissions Inventory-Derived Criteria 

Pollutant Ratios 

For the selected sites, TNMOC/NOx and CO/NOx ratios from the ambient and emissions 

inventory data were computed by day-of-week (weekday5, Saturday, and Sunday), month (June, 

July, and August), and summer season (June-August). Because CO data were available for 

winter and summer months, CO/NOx ratios were also calculated for individual winter months 

(December, January, and February) and the winter season (December-February). 

Ambient-derived ratios were compared with emissions inventory-derived ratios by spatially 

matching ambient data to corresponding groups of 4-km x 4-km grid cells surrounding each 

ambient monitoring site. These groups of grid cells were identified for each site based on 

predominant wind speeds during the early morning hours (0600–0900). 

Because meteorological factors can affect differences between ambient- and emissions 

inventory-derived ratios, several different ratio comparisons were considered, each representing 

a different spatial configuration of wind quadrants and grid cells around each site. The extent of 

each quadrant-grid cell configuration, or analysis zone, was based on the maximum distance an 

air parcel could travel during the 3-hour sampling period, given average wind speeds during that 

period. Figure 1-2 illustrates an example of a full extent grid analysis zone6

 centered on an 

ambient monitoring site and shows the wind quadrant definitions, whose extents vary according 

 

3

 For on-road mobile sources, emissions were provided for January and July only. For biogenic sources, emissions 

were provided for each day of 2005. Additional details on the processing of emissions data for these source 

categories are provided in Section 2.2.1. 

4

 For 2005, biogenic emissions were provided as CAMx-ready binary files, on-road emissions were provided as 

PostgreSQL files, and the remaining source sectors were provided as SAS files. All 2008 data were provided as 

SAS files. 

5

 For pollutant ratio comparisons and all remaining analyses, ambient data from Tuesday–Thursday were considered 

“weekday.” Emissions inventory data were not provided for individual weekdays. 

6

 The full extent grid analysis zone surrounding each site is based on the quadrant analysis zone with the highest 

average wind speed. 
Upper Midwest Emissions Inventory Evaluation Introduction 

1-5

to the observed wind speeds at each site. The center point of the grid represents the ambient 

monitoring site, the hollow grid represents the entire grid analysis zone, and the colored regions 

represent the wind quadrant analysis zones. The individual wind quadrant analysis zones are 

larger for quadrants where wind speeds are greater and smaller for quadrants where wind speeds 

are light. For the Gary site and three of the Chicago area sites, the grid analysis zone consists of 

a 9 x 9 grid cell region7 with the monitoring site in the center cell. For the Northbrook site in 

Chicago and the sites in Detroit and Milwaukee—where average morning wind speeds were 

lower—the grid analysis zone consists of a 7 x 7 grid cell region around each monitoring site 

(see Table 1-2). 

Wind Quadrant 1 (1-90°) Wind Quadrant 2 (91-180°) Wind Quadrant 3 (181-270°) Wind Quadrant 4 (271-360°)

Figure 1-2. Example of a full extent grid analysis zone, showing the spatial configuration 

of grid cells for which ambient- and emissions inventory-derived ratio comparisons were 

calculated. The monitoring site is represented by a small triangle. 

Table 1-2. Dimensions of the full grid analysis zone around each monitoring site of interest. 

Site Name 

Dimensions of 

Grid Analysis 

Zone 

Area of Grid 

Analysis Zone (km2) 

Chicago, IL – Jardine 9 x 9 cells 1,296 

Chicago, IL – Northbrook 7 x 7 cells 784 

Chicago, IL – Franklin 9 x 9 cells 1,296 

Chicago, IL – Mannheim 9 x 9 cells 1,296 

Gary, IN 9 x 9 cells 1,296 

Detroit, MI – E7Mile 7 x 7 cells 784 

Detroit, MI – Linwood 7 x 7 cells 784 

Milwaukee, WI 7 x 7 cells 784 

To make consistent comparisons of total hydrocarbons between the ambient data and the 

emissions inventory, the emissions inventory data were converted from mass to molar units. In 

 

7

 Note that each individual grid cell measures 4 km x 4 km, so the total area of a 9 x 9 grid cell region is 1,296 km2, 

as shown in Table 1-2. 
Upper Midwest Emissions Inventory Evaluation Introduction 

1-6

addition, the individual chemical species reported in the emissions inventory were matched to 

those in the ambient data, and only TNMOC species that are identified by the PAMS program 

(i.e., PAMSHC, or the sum of PAMS-identified hydrocarbons) were included in the analyses. 

Appendix A contains the detailed chemical species cross-reference list that was used to match 

emissions inventory species to the ambient species. 

1.2.3 Comparison of Ambient- and Emissions Inventory-Derived Hydrocarbon 

Compositions 

In addition to ratio comparisons, the chemical composition of hydrocarbons reported in 

the emissions inventory was compared to the chemical composition of the ambient air at 

individual monitoring sites. These “fingerprint” analyses were used to determine how accurately 

the speciation of the emissions inventory compares to the data measured at the ambient 

monitoring sites. Fingerprint analyses were performed for each site by day of week (weekday, 

Saturday, and Sunday), month (June, July, August), and wind quadrant. 

As a further review of the speciation of the emissions inventory, STI also computed and 

compared the relative reactivity of the organic species in the emissions inventory and ambient 

data. The reactivity of each species was estimated using published maximum incremental 

reactivity (MIR) values that represent the ozone formation potential of various organic 

compounds (Carter, 2003). Weighted reactivity values for the emissions inventory and ambient 

data will be calculated as follows: 

R = 

n

i 1

(MIR)iwi

where: 

R = weighted reactivity 

(MIR)i = maximum incremental reactivity for species i 

wi = weight fraction of species i in the emissions inventory or ambient data 

Reactivity comparisons were performed by day of week (weekday, Saturday, and 

Sunday), month (June, July, August), and wind quadrant for each monitoring site. 

1.3 Uncertainty Issues 

Understanding the uncertainties associated with comparisons of ambient- and emissions 

inventory-derived pollutant ratios is essential to assess the suitability of top-down evaluation 

analyses. Three general categories of uncertainty issues are associated with top-down emissions 

reconciliation analyses: (1) accuracy of the emissions inventory, (2) accuracy of the ambient 

concentration measurements, and (3) suitability of comparisons. 

1.3.1 Emissions Inventory Uncertainties 

To compare ambient pollutant ratios to emissions inventory ratios, it is important to 

accurately characterize, to the extent possible, the magnitude, spatial distribution, chemical 

composition, and diurnal pattern of emissions. Uncertainties and inaccuracies associated with 

emissions inventory data generally stem from (1) emissions estimation techniques and 
Upper Midwest Emissions Inventory Evaluation Introduction 

1-7

(2) emissions processing techniques. Inaccuracies and uncertainties associated with emissions 

estimation techniques include misclassification or exclusion of major emissions sources, the use 

of incorrect emissions activity data, the use of incorrect emission factors, and the use of incorrect 

chemical speciation profiles. For on-road mobile sources, which are key emissions sources 

impacting the monitoring sites addressed in the project—particularly during the morning periods 

evaluated—emissions estimates have historically been prepared using EPA’s MOBILE6.2 

model. The MOBILE6.2 model, which was used in the development of LADCO’s 2005 Base M 

inventory, calculates gram per mile emission rates for on-road mobile sources operating under 

various conditions, and though model outputs have been compared to data from tunnel studies 

and other “real-world” data (Pollack et al., 2004), EPA does not provide estimates of its 

uncertainty. Recently, EPA has replaced MOBILE6.2 with the MOVES model, which is based 

on updated emissions test results (U.S. Environmental Protection Agency, 2010). LADCO’s 

2008 emissions inventory was developed using MOVES. 

To perform a top-down emissions inventory evaluation, emissions estimates must be 

spatially and temporally resolved for the region surrounding the ambient monitoring sites. To 

accomplish this task, hourly gridded emissions estimates of VOC, NOx, and CO were acquired 

from LADCO. The methods used to disaggregate annual average countywide total emissions 

estimates into gridded, hourly data can introduce inaccuracies into the emissions inventory data. 

For example, spatial surrogate data that are not representative of the locations of emissions 

sources can result in misrepresentation of the geographic location of emissions sources. 

Similarly, temporal profiles that are not representative of the monthly, weekly, and diurnal 

distribution of emissions source activity can result in misrepresentation of the diurnal activity 

patterns for sources within the vicinity (grid cells) of the ambient monitor. 

To perform a top-down emissions inventory evaluation, emissions estimates must also be 

chemically resolved, with VOC emissions disaggregated into individual chemical species. STI 

used speciation profiles and cross-reference files provided by LADCO to perform this step. 

Emissions inventory uncertainties can be introduced during the speciation process through the 

incorrect assignments of speciation profiles to emissions sources and/or by speciation profiles 

that do not represent the chemical source composition. 

1.3.2 Ambient Measurement Uncertainties 

Uncertainties associated with ambient measurements include instrument detection limits, 

precision of measurements, and sampling and handling losses. Prior to conducting an emissions 

inventory evaluation, the ambient data measurement methods should be assessed to ensure that 

the collection methods yield adequate data for this type of analysis. Furthermore, the ambient 

data sets intended for use must be quality-assured to eliminate invalid samples. For this study, 

ambient data were subjected to a data validation process that followed established protocols. 

1.3.3 Uncertainties Associated with the Comparisons 

Uncertainties associated with the comparison of ambient and emissions inventory data 

arise from the spatial and temporal matching of ambient and emissions inventory data, 

meteorological factors, and atmospheric reactions. To minimize differences between 

ambient- and emissions inventory-derived ratios due to mismatches in time and space, it is best 
Upper Midwest Emissions Inventory Evaluation Introduction 

1-8

to use emissions estimates as close to the vintage of the ambient data as practical. For this study, 

emissions estimates representative of the winter and summer of 2005 were compared to ambient 

data for the winters and summers of 2004, 2005, and 2006, and emissions estimates 

representative of the winter and summer of 2008 were compared to ambient data for the winter 

and summer of 2008.8

A major premise of the top-down evaluation is that only monitoring sites and sampling 

periods that are dominated by fresh emissions should be considered in the analysis. It is possible 

that temporal uncertainties may be caused by early morning ambient ratios that include carryover 

emissions in which PAMSHC and/or NOx have been preferentially removed by chemical 

conversion overnight. Spatial uncertainties due to different influences of surface and aloft 

emissions may arise. For example, PAMSHC, CO, and NOx emissions from nearby elevated 

sources may be injected aloft and, as a result, may not mix into the surface air sample. 

Meteorological factors such as wind speed, direction, and mixing depth determine the 

spatial distribution of emissions and thus determine which emissions are sampled. Atmospheric 

reactions modify the species distribution and mass of midday and afternoon ambient samples. 

Thus, comparisons from midday and afternoon periods are likely to be less reliable than morning 

comparisons. 

1.4 Summary of Results 

The on-road mobile source component of LADCO’s 2005 emissions inventory was 

developed using EPA’s MOBILE6.2 model and link-level activity data. The top-down 

evaluation for the 2005 emissions inventory indicates that, in general, on-road mobile sources are 

represented accurately in the emissions data. This conclusion is based on the fact that agreement 

between ambient- and emissions-inventory-derived pollutant ratios was closest (±20%) for 

wintertime CO/NOx ratios, and on-road mobile sources accounted for 57% to 80% of wintertime 

CO and NOx emissions at all sites for which ratios were calculated. For sites in the Chicago 

area, agreement between ambient- and emissions inventory-derived pollutant ratios was as close 

as could be expected, given the limitations of the analysis techniques. However, comparisons 

with ambient data indicate that the emissions inventory for Sundays may not be representative of 

actual activity patterns on that day of the week, perhaps due to decreases in on-road mobile 

source emissions from Saturdays to Sundays, as well as inaccurate temporal characterizations of 

other source categories. In addition, sources of VOC emissions appear to be missing or 

underrepresented in the emissions inventory near sites that are influenced by industrial and 

residential emissions, such as the Gary site and the East 7 Mile site in Detroit. 

The on-road mobile source component of LADCO’s 2008 emissions inventory was 

developed using EPA’s MOVES model with default input data, and county-level outputs from 

MOVES were spatially allocated using spatial surrogate data.9 For the 2008 inventory, 

agreement between ambient- and emissions-inventory derived pollutant ratios was generally 

 

8

 Ambient data from 2009-2010 were also evaluated as part of this project but were not compared directly with 

emissions data. 

9

 LADCO plans to update the 2008 inventory with state-specific MOVES inputs and link-level activity data. The 

2008 inventory used in this analysis was the most current version as of April 29, 2011. 
Upper Midwest Emissions Inventory Evaluation Introduction 

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poorer than was observed for the 2005 inventory. The greater discrepancy between ambient- and 

emissions inventory-derived pollutant ratios primarily results from large decreases in on-road 

NOx emissions from 2005 to 2008 that outpaced reductions in ambient NOx concentrations. 

However, the Saturday-to-Sunday differences in pollutant ratio comparisons observed for the 

2005 inventory were not observed for the 2008 inventory, as there was no variation between 

Saturday and Sunday on-road mobile source emissions in the 2008 inventory (as was the case for 

2005). 

For both 2005 and 2008, the speciation of the VOC emissions inventory at all sites does 

not compare well with the hydrocarbon composition of the ambient data, resulting in a VOC 

emissions inventory that is more reactive (i.e., prone to contribute to ozone formation) at all sites 

than the corresponding ambient data. As a result, ozone modeling efforts for the region may be 

influenced by “compensating errors,” as the underestimated magnitude of VOC emissions is 

offset by the overestimated reactivity of those emissions. Key findings that support these 

conclusions include: 

 For 2005, the agreement between overall ambient- and emissions inventory-derived 

CO/NOx ratios is good (±30%) across all sites, particularly for winter months, and onroad mobile sources dominate the wintertime CO and NOx inventories for all sites. 

 For 2008, the agreement between overall ambient- and emissions inventory-derived 

CO/NOx ratios is poorer (±60%) across all sites, and on-road mobile sources continue to 

dominate the CO and NOx inventories for all sites. 

 For both 2005 and 2008, the agreement between overall ambient- and emissions 

inventory-derived TNMOC/NOx ratios is good (±20%) for Chicago’s Jardine (2005 only) 

and Northbrook sites. 

 For 2005, the agreement between overall ambient- and emissions inventory-derived 

TNMOC/NOx ratios is poorest at the Detroit East 7 Mile site and the Gary site, which are 

likely to be affected by industrial and residential emissions sources. 

 For 2005, the agreement between ambient- and emissions inventory-derived 

TNMOC/NOx and CO/NOx ratios is generally better on weekdays and Saturdays than on 

Sundays. For 2008, the agreement between ambient- and emissions inventory-derived 

pollutant ratios is generally similar across all days. 

 Comparison with the ambient data shows that the speciation of the emissions inventory 

tends to overestimate the contribution of some species (e.g., acetylene, ethylene, toluene, 

and isoprene) and underestimate the contribution of other species (e.g., ethane, propane, 

and C6-C11 alkanes). 

 Across all sites, the overall weighted reactivity of the species present in the emissions 

inventory for the summer season is 16% to 80% higher than the weighted reactivity of the 

species present in the ambient data. 

A detailed description of the analysis techniques and results that served as the basis for 

these conclusions and recommendations is provided in the sections that follow. 

Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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2. Data Acquisition and Processing 

Preparing ambient concentration, meteorological, and emissions inventory data for use in 

a top-down emissions inventory evaluation involves several steps. This section presents a 

detailed discussion of the data preparation and processing performed for this emissions 

evaluation. 

2.1 Ambient Monitoring Data 

2.1.1 Ambient Data Acquisition 

To support this top-down emissions evaluation, air quality and meteorological data for 

the years 2004–2006 and 2008–2010 were acquired from AQS for eight monitoring sites in the 

Upper Midwest. To effectively evaluate on-road mobile source emissions estimates, an effort 

was made to focus on monitoring sites that are likely to be impacted by fresh mobile source 

emissions. However, some of the sites included in these analyses were in the vicinity of other 

emissions sources, including non-road mobile sources (e.g., the Jardine and Mannheim sites in 

Chicago) and industrial sources (e.g., the Gary site), as described in Section 2.2. 

Hourly data for summer (June–August) and winter (December–February) months were 

acquired from AQS for speciated hydrocarbons (HC), TNMOC, carbonyl compounds, CO, NOx, 

wind speed, and wind direction. For the 2004–2006 period, hourly HC data are available for 

summer months at only five sites in the region. Available winter HC data are limited to 24-hour 

measurements of a small number of species (e.g., benzene and toluene) collected every six days, 

making these data insufficiently time-resolved for further analyses.10 For CO and NOx, hourly 

data are available for summer and winter months for all cities except Gary, for which wintertime 

CO data are unavailable (see Table 2-1). 

Hourly HC data for 2008 and 2009 are available for summer months at the ChicagoNorthbrook site, and for 2008 only at the Milwaukee site. Hourly CO and NOx data are available 

for 2008, 2009, and the first quarter of 2010 at three sites in the Chicago area (see Table 2-1). 

 

10 Comparisons between ambient data and emissions data are generally limited to morning hours, when ambient 

concentrations are most likely to be influenced by fresh pollutants (i.e., emission rates are high and chemical 

reaction rates are low). 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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Table 2-1. Hourly data available at individual monitoring sites (S=summer; W=winter). 

Site Name HC NOx CO Wind Data 

2004-2006 Data Availability 

Chicago-Jardine S S/W S/W 

Chicago-Northbrook S S/W S/W 

Chicago-Mannheim S/W S/W S/W 

Chicago-Franklin S/W S/W 

Gary S S/W S/W 

Detroit-Linwood S/W S/W 

Detroit-E7Mile S S/W S/W 

Milwaukee S S/W S/W S/W 

2008 Data Availability 

Chicago-Jardinea S S/W 

Chicago-Northbrookb S S/W S/W S/W 

Chicago- Mannheim S/W S/W S/W 

Chicago-Franklin S/W S/W 

Garya S/W S/W 

Milwaukee S S/W S/W 

2009c Data Availability 

Chicago-Jardinea S S/W 

Chicago-Northbrook S S/W S/W S/W 

Chicago-Mannheim S/W S/W S/W 

Chicago-Franklin S/W S/W 

Detroit-E7Mile S/W S/W 

Gary, INa S/W S/W 

Milwaukee S/W S/W 

a Though 2008–2009 TNMOC data for the Jardine and Gary sites were not found in AQS, these data may 

be available from state agencies. However, the data were not available for use in these analyses. b The only winter data available for Northbrook are from December 2008 (no January/February data 

available). 

c Data available for January and February of 2010 were included in 2009 winter analyses. At the time 

analyses were conducted, NOx and CO data were available for the first quarter of 2010 at the Northbrook, 

Mannheim, and Franklin sites in Chicago. 

2.1.2 Ambient Data Validation 

Data validation was performed to identify a representative data set for each monitoring 

site of interest. Ambient data from 2004–2006 and 2008–2010 were brought into a Microsoft 

Access database, sorted, and imported into the Volatile Organic Compound Data Validation and 

Analysis Software (VOCDat) for validation. VOCDat allows visual inspection of the data and 

application of screening criteria. To ensure quality data for analysis, established protocols for 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

2-3

validation of the VOC data were followed. Data validation methods included inspection of time 

series (e.g., TNMOC with total alkanes, alkenes, aromatics, carbonyl compounds, NOx and 

ozone), scatter plots (e.g., benzene/acetylene, benzene/toluene, ethane/propane, TNMOC/groups 

of species) and fingerprint plots (i.e., plots showing the concentration of each species in a 

sample). Data quality issues identified during the validation process included: 

 Data outliers – Data outliers were defined as a single sample spike in concentration 

observed in a species or group of species. These high values were excluded from 

analysis because, even if the measurements were truly representative of ambient 

conditions during that hour, the values are not representative of the typical influence of 

emissions sources around the monitoring site and would skew the overall average. An 

example of a single sample high value from the Gary, Indiana, PAMS site is shown in 

Figure 2-1. This propane measurement may have been real but was more than 10 times 

higher than typical measurements at this site; this value was not included in subsequent 

analyses. 

 Low concentration values – Abnormally low concentration values were also addressed 

by the data validation. For example, ethane and propane typically correlate well with one 

another, but there were samples at the Chicago-Jardine site in which ethane values were 

low relative to propane. Therefore, measurements were flagged as suspect when ethane 

values were less than 1 ppbC while propane values were greater than 2 ppbC. Typically, 

ethane concentrations drop below 2 ppbC only when there are problems with the 

analytical system. This problem occurred only at the Jardine site for the time period of 

interest. 

Figure 2-1. Time series of propane and ethane concentrations (ppbC) at Gary, IN. 

Ethane 

Propane 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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 Shifts in species patterns – In some cases, shifts in measurements for a given species 

were unlike measurements during the previous and following weeks. For example, the 

CO baseline at Detroit Linwood site typically falls in the range between 100 ppb to 

300 ppb. However, CO concentrations dropped to zero from July 22 to July 26, 2006 

(see Figure 2-2). Data from this anomalous period were excluded from subsequent 

analyses. In addition, TNMOC measurements at the Northbrook site in Chicago 

increased sharply from 2005 to 2009. However, these increases were largely associated 

with the unidentified portion of TNMOC (see Figure 2-3), which may indicate changes 

in instrument sensitivity post-2005. The higher TNMOC measurements for 2008 and 

2009 were included in our analyses but should be viewed with caution.11

Data quality issues identified during the validation process resulted in data being flagged 

as suspect and excluded from subsequent analyses. For the 2004–2006 time period, only about 

10% of the data were flagged as suspect for summer months, and only about 8% of the data were 

flagged as suspect for winter months. For the 2008–2010 time period, only about 4% of the data 

were flagged as suspect for summer months, and only about 1% of the data were flagged as 

suspect for winter months. 

Figure 2-2. Time series of CO concentrations (ppb) for Linwood site in Detroit, MI. 

 

11 It should also be noted that a significant amount of repair work occurred at the Northbrook site during 2008 and 

2009. though this work did not directly involve the TNMOC instrument (auto-GC). 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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0

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Figure 2-3. Yearly variations in summer weekday TNMOC concentrations (ppbC) at the 

Northbrook site in Chicago, IL. 

2.1.3 Ambient Site Characterization 

To help characterize the land use patterns and emissions sources surrounding each 

ambient monitoring site and to verify that all sites were likely to be significantly impacted by 

mobile source emissions, digital images of the 5 km x 5 km area around each site were generated 

using Google Earth. In addition, photographs taken around several of the monitoring sites are 

provided in Appendix B, as well as digital images of a larger area (28 km x 28 km)12 around 

each site. A description of the area around each monitoring site appears below. 

 

12 The grid analysis zones around individual monitoring sites were all at least 7 x 7 grid cells, or 28 km x 28 km. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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Chicago – Jardine and Franklin 

The Chicago-Jardine site is located at the Jardine Water Filtration Plant on the shore of 

Lake Michigan. The site is east of downtown Chicago and about 0.7 km from Highway 41, 

making it subject to significant emissions from pleasure craft and commercial marine vessels, 

especially during summertime. The Chicago-Franklin site is in downtown Chicago about 3 km 

southwest of the Jardine site and about 0.2 km north of the Eisenhower Expressway (see 

Figure 2-4), making it an ideal site for capturing the effects of fresh downtown mobile 

emissions. 

Figure 2-4. Image of the area around the Jardine and Franklin sites in Chicago. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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Chicago – Northbrook 

The Chicago-Northbrook site is located at the Northbrook Water Plant in a northern 

suburb of Chicago. The site is about 0.7 km south of the Tri-State Tollway and about 0.7 km 

west of a major highway (see Figure 2-5). 

Figure 2-5. Image of the area around the Northbrook site in Chicago. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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Chicago – Mannheim 

The Chicago-Mannheim site is about 22 km northwest of downtown Chicago adjacent to 

O’Hare International Airport (see Figure 2-6) and subject to significant aircraft and airportrelated emissions. The site is 0.2 km north of a toll booth on the Tri-State Tollway. 

Figure 2-6. Image of the area around the Mannheim site in Chicago. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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Gary 

The Gary site is just south of the Mittal Steel Works and about 1.5 km northeast of 

downtown Gary. The site is about 0.6 km north of the interchange that connects two interstate 

highways (see Figure 2-7). 

Figure 2-7. Image of the area around the Gary site. 
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Detroit – East 7 Mile and Linwood 

The East 7 Mile and Linwood sites are both located in residential areas. The East 7 Mile 

site is about 11 km northeast of downtown Detroit, 4 km north of Interstate 94, and 4 km 

southeast of the Daimler Chrysler Warren Plant. The Linwood site is about 3 km northwest of 

downtown Detroit and is adjacent to several arterial roads, including the Rosa Parks Memorial 

Highway (see Figure 2-8). 

Figure 2-8. Image of the area around the East 7 Mile and Linwood sites in Detroit. 

Milwaukee 

The Milwaukee site is located in a largely urban and residential area about 2.5 km north 

of downtown Milwaukee and 3 km west of Lake Michigan. The site is about 0.5 km east of 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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Highway 43 and about 3 km northeast of the Marquette Interchange that connects Interstates 94 

and 43 near downtown Milwaukee (see Figure 2-9). 

Figure 2-9. Image of the area around the Milwaukee site. 

2.1.4 Ambient Concentration Data 

For sites with summer TNMOC measurements, morning (0600–0900) concentrations of 

TNMOC and NOx were summarized by day of week for data from 2004–2006 and 2008–2009 

(see Table 2-2). For 2005, mean morning TNMOC concentrations were highest at the Gary site 

and the East 7 Mile site in Detroit, which is likely due to a greater density of industrial emissions 

sources around those sites. TNMOC concentrations were 13% to 34% lower on weekend days 

relative to weekdays, with the Chicago-Jardine and Milwaukee sites having the largest weekend 

decreases in TNMOC concentrations. At all sites except the Milwaukee site, Sunday TNMOC 

concentrations were about the same as or higher than Saturday TNMOC concentrations in 2005. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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Although mean morning NOx concentrations did not vary among sites as widely as mean 

TNMOC concentrations did, NOx concentrations were also lower on weekend days, decreasing 

by 11% to 53% on Saturdays and Sundays relative to weekdays. At all sites except the Jardine 

site, Sunday NOx concentrations were lower than Saturday NOx concentrations by 16% to 40%. 

At the Gary site, Saturday NOx concentrations were more similar to weekday concentrations than 

to Sunday concentrations. 

For 2008, ambient TNMOC measurements were only available at the Northbrook and 

Milwaukee sites. At Northbrook, TNMOC concentrations were slightly higher in 2008 than in 

2004–2006, while weekday NOx concentrations were 13% lower in 2008 than in 2004–2006.13 

At the Milwaukee site, weekday TNMOC concentrations were 24% higher in 2008 than in 

2004-2006, while weekday NOx concentrations decreased by 16% in 2008 (see Table 2-2). 

For 2009, ambient TNMOC measurements were only available at the Northbrook site, 

where 2009 TNMOC concentrations were significantly higher than in previous years (see 

Table 2-2). However, it should be noted that there were potential instrument issues at 

Northbrook, as described in Section 2.1.2 above. 

Table 2-2. Mean summer TNMOC and NOx concentrations. 

TNMOC (ppbC) NOx (ppb) Site 

Weekday Saturday Sunday Weekday Saturday Sunday 

2004-2006 Data 

Chicago-Jardine 43.9 30.1 37.5 30.3 14.3 16.7 

Chicago-Northbrook 45.6 36.9 39.7 23.5 16.2 11.8 

Milwaukee 74.8 59.8 49.7 21.9 13.1 11.0 

Gary 142.4 122.0 119.2 26.2 23.2 13.8 

Detroit-E7 Mile 157.8 131.6 132.3 22.2 14.4 10.4 

2008 Data 

Chicago-Northbrook 47.3 37.8 43.9 20.5 10.2 10.1 

Milwaukee 92.5 81.8 69.9 18.3 11.3 6.8 

2009 Data 

Chicago-Northbrook 67.3 61.9 74.6 14.2 8.9 6.7 

For sites with summer and winter CO measurements, morning (0600–0900) 

concentrations of CO and NOx were summarized by day of week for data from 2004–2006 and 

2008–2009 (see Tables 2-3 and 2-4). In general, mean morning CO and NOx concentrations 

were higher in winter than in summer, which is likely due to both meteorological conditions 

(e.g., lower mixing heights in winter) and increased CO emissions from light-duty vehicles in 

 

13 Weekend NOx concentrations for 2008 at Northbrook showed a sharper decrease on Saturdays than on Sundays 

relative to data from 2004–2006, but note that the use of data from only one summer limits the sample size for 

individual days of the week. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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winter.14 CO and NOx concentrations for both summer and winter were highest at the Franklin 

and Mannheim sites in Chicago. Across all years, CO concentrations were 5% to 45% lower on 

weekend days relative to weekdays, with the Chicago-Franklin site having the largest weekend 

decrease in CO concentrations. NOx concentrations were 15% to 77% lower on weekend days 

relative to weekdays, with the Chicago-Franklin site again having the largest weekend decrease 

in concentrations. 

Ambient data from the Chicago-Mannheim site showed that summer and winter CO 

concentrations decreased by about 40% in 2008 compared to 2004–2006. Measurements of NOx

concentrations in 2008 showed a decrease of about 13% in the winter and little change in the 

summer compared to 2004–2006. At the Chicago-Franklin site, winter CO concentrations in 

2008 decreased by about 20% compared to 2004–2006 (see Table 2-4). 

For 2009, CO concentrations at the Mannheim site increased relative to 2008, particularly 

for summer months, while NOx concentrations continued to decrease. At the Franklin site, both 

CO and NOx concentrations decreased between 2008 and 2009. At the Northbrook site, CO and 

NOx concentrations generally increased between 2008 and 2009 for winter months and decreased 

for summer months. It should also be noted that 2009 wintertime NOx concentrations decreased 

by 45% on Saturdays at the Franklin and Mannheim sites relative to 2008, while weekday and 

Sunday concentrations decreased by less than 20%. This sharper decrease on Saturdays may be 

due to reduced heavy-duty truck traffic on Saturdays as a result of the recent economic 

downturn. However, at the Northbrook site, weekend NOx concentrations rose sharply between 

2008 and 2009, while weekday NOx concentrations were virtually unchanged. 

Table 2-3. Mean summer (June–August) CO and NOx concentrations. 

CO (ppb) NOx (ppb) Site 

Weekday Saturday Sunday Weekday Saturday Sunday 

2004-2006 Data

Chicago-Franklin 643 371 417 85.9 37.7 25.0 

Chicago-Mannheim 541 440 384 76.4 44.5 27.1 

Milwaukee 306 266 263 21.9 13.1 11.0 

Detroit-Linwood 414 304 318 34.9 21.8 16.3 

2008 Data 

Chicago-Franklin 641 439 389 88.2 40.3 20.1 

Chicago-Mannheim 331 255 212 73.1 44.4 30.0 

Chicago-Northbrook 227 196 198 21.0 10.5 9.2 

2009 Data 

Chicago-Franklin 471 335 313 57.9 31.8 20.4 

Chicago-Mannheim 388 304 283 55.6 26.8 19.5 

Chicago-Northbrook 210 184 178 14.2 8.9 6.7 

 

14 Note that the Franklin site was an exception to this pattern in 2008, when summer weekday CO concentrations 

were 11% higher than corresponding winter concentrations. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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Table 2-4. Mean winter (December–February) CO and NOx concentrations. 

CO (ppb) NOx (ppb) 

Site 

Weekday Saturday Sunday Weekday Saturday Sunday 

2004-2006 Data 

Chicago-Franklin 742 520 411 119.1 61.3 38.9 

Chicago-Mannheim 745 560 487 132.6 75.1 55.4 

Milwaukee 448 425 338 49.5 41.6 21.6 

Detroit-Linwood 510 476 429 57.1 48.3 39.8 

2008 Data 

Chicago-Franklin 579 433 350 111.8 66.0 40.8 

Chicago-Mannheim 436 310 283 115.6 68.0 47.8 

Chicago-Northbrooka 282 199 199 42.8 11.9 16.4 

2009b Data 

Chicago-Franklin 524 422 360 90.7 36.3 39.4 

Chicago-Mannheim 463 304 331 93.5 36.2 41.7 

Chicago-Northbrook 335 256 269 41.9 18.9 28.7 

a Wintertime concentrations listed for the Northbrook site represent the month of December 2008 only. b Wintertime concentrations listed for 2009 include available data from January and February 2010. 

Diurnal patterns of TNMOC, NOx, and CO concentrations were explored using notched 

box whisker plots (Figure 2-10). Across all years, weekday TNMOC, NOx, and CO 

concentrations generally showed a morning peak, consistent with traffic activity, and an 

afternoon decrease, which could be a function of both decreased traffic activity and increased 

atmospheric mixing. Diurnal plots of pollutant concentrations for 2004–2006 are shown in 

Figures 2-11 through 2-18, and diurnal plots for additional years are provided in Appendix C. 

On weekend days, a small increase in concentrations is generally observed for both TNMOC and 

NOx just after noon, consistent with delayed traffic activity on weekends compared to weekdays 

(also seen by Chinkin et al., 2002). At Jardine (Figure 2-11), the diurnal profile for TNMOC on 

weekend days is much flatter than on weekdays (i.e., concentrations vary less from hour to hour). 

However, at Northbrook, the weekend and weekday diurnal profiles for TNMOC are very 

similar (Figure 2-12). For CO, diurnal variations are somewhat dampened by the resolution of 

the data. In addition, the instrument used at the Gary site appears to have a detection limit of 250 

ppb, so there are no data below that value. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

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Figure 2-10. Interpretation of notched box whisker plots produced by SYSTAT. Boxes 

show the 25th to 75th percentiles (interquartile range, or IQR); whiskers extend to 1.5IQR; 

and concentrations beyond the whiskers are designated by asterisks. Concentrations 

beyond 3IQR are designated with open circles. The median and 95% confidence 

intervals (C.I.) are shown by a notch.
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Figure 2-11. Hourly TNMOC and NOx concentrations for the Chicago-Jardine site for summer weekdays (left), Sa

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Figure 2-12. Hourly TNMOC and NOx concentrations for the Chicago-Northbrook site for summer weekdays (left)

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Figure 2-13. Hourly TNMOC and NOx concentrations for the Gary site for summer weekdays (left), Saturdays (cen

Sundays (right), 2004–2006. 
2-19

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Figure 2-14. Hourly TNMOC and NOx concentrations for the Detroit-East 7 Mile site for summer weekdays (left), S

(center), and Sundays (right), 2004–2006. 
2-20

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Figure 2-15. Hourly TNMOC, NOx, and CO concentrations for the Milwaukee site for summer weekdays (left), Sat

and Sundays (right), 2004–2006. 
2-21

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Figure 2-16. Hourly CO and NOx concentrations for the Chicago-Mannheim site for summer weekdays (left), Satu

and Sundays (right), 2004–2006. 
2-22

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Figure 2-17. Hourly CO and NOx concentrations for the Chicago-Franklin site for summer weekdays (left), Saturda

and Sundays (right), 2004–2006. 
2-23

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Figure 2-18. Hourly CO and NOx concentrations for the Detroit-Linwood site for summer weekdays (left), Saturday

Sundays (right), 2004–2006.
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

 2-24

2.1.5 Ambient Data Screening 

As described in Section 1.3.3, a major premise of the top-down evaluation is that only 

monitoring sites and sampling periods that are dominated by fresh emissions are considered in 

the analysis. Therefore, ambient measurements that do not exceed background thresholds were 

not included in the data sets used to calculate pollutant ratios. For this analysis, we used 

concentration thresholds of VOC > 50 ppbC, NOx > 10 ppb, and CO > 0.150 ppm (Chinkin and 

Reid, 2006; LADCO, 1998). 

2.2 Emissions Inventory Data 

2.2.1 Emissions Data Acquisition and Processing 

LADCO provided 2005 Base M emissions inventory data files and supporting files (e.g., 

speciation profile libraries) for area, point, non-road mobile, on-road mobile and biogenic 

sources. LADCO’s anthropogenic emission files contain criteria pollutant emissions that have 

been spatially resolved to a 4-km grid resolution and temporally resolved to an hourly basis. For 

all anthropogenic source sectors other than on-road mobile sources, emissions data were 

provided for a representative weekday, Saturday, and Sunday in each month of 2005. For 

on-road sources, gridded criteria pollutant emissions were provided for a January weekday, 

Saturday, and Sunday, and air quality model-ready emission inputs were provided for January 

and July weekdays, Saturdays, and Sundays. For biogenic sources, hourly emissions data for 

isoprene and other air quality model-ready biogenic species were provided at a 12-km grid 

resolution for each day of 2005. Emissions grid domains and file formats varied by source sector 

(see Figure 2-19 and Table 2-5), with file formats including SAS, PostgreSQL, and CAMx 

binary. 

For 2008, LADCO provided Base B (on-road and non-road mobile sources) and Base C 

(area and point sources) anthropogenic15 inventories at the same spatial (4-km) and temporal 

(hourly) resolution as the 2005 emissions inventories. All 2008 emissions were provided in SAS 

format for the innermost grid domain shown in Figure 2-19, and files for a representative 

weekday, Saturday, and Sunday in each month were again made available. For on-road mobile 

sources, 2008 emissions were generated by running the MOVES model with county-level default 

data for the region, then gridding the county-level emissions using spatial surrogate data.16 By 

contrast, the 2005 on-road inventory was developed at the link level using MOBILE6.2 emission 

factors within the Consolidated Community Emissions Processing Tool (CONCEPT).17 As a 

result, some differences between the 2005 and 2008 on-road inventories result from this change 

in models, rather than from changes in vehicle fleets and activities alone. 

 

15 Biogenic emissions for 2008 were not available, so emissions from this source sector were held constant from 

2005. 

16 For light-duty vehicles, LADCO used a hybrid surrogate that combined vehicle miles traveled (weighted 75%) 

with population data (weighted 25%). For trucks, LADCO used miles traveled on rural secondary roads as the 

spatial surrogate. 

17 For subsequent versions of the 2008 on-road inventory, LADCO will replace MOVES default data with local 

information on vehicle characteristics and activities and will generate link-level emissions using CONCEPT. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

 2-25

Figure 2-19. Emissions grid domains for the LADCO 2005 Base M inventories. 

Table 2-5. LADCO emissions inventory files for January 14, 2005. 

File Name Description 

areaemis.sas7bdat.050114.other_baseM_v3_4km SAS file for area source emissions 

areaemis.sas7bdat.050114.mar_baseM_4km SAS file for marine, aircraft, and rail 

emissions 

areaemis.sas7bdat.050114.nonroad_baseM_v3_4km 

SAS file for non-road mobile source 

emissions other than marine, aircraft, 

and rail 

ptemis.sas7bdat.050114.egu_baseM_4km SAS file for electrical generating units 

(EGUs) 

ptemis.sas7bdat.050114.pt_nonutil_baseM_4km SAS file for non-EGU point sources 

ocin_[network]_01142005_01.mv_emissions_raw.sql 

PostgreSQL file for on-road mobile 

source emissions (files provided for 

transportation networks covering 

Chicago, Milwaukee, Gary, and 

Detroit) 

camx_mv.[network]_01142005_01.base.out.200514.bin CAMx-ready on-road emissions file 

biog.20050114.upmw.12.megan.ld.bin CAMx-ready biogenic emissions file 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

 2-26

To prepare the emissions data for use in subsequent analyses, we converted all data files 

to a common CSV format. We then extracted data records for the grid cells included in the grid 

analysis zones around each of the eight monitoring sites of interest. These grid analysis zones 

were identified for each site on the basis of predominant wind speeds during the early morning 

hours (0600–0900), as described in Section 1.2.2. For the Gary site and three of the Chicago 

area sites, the grid analysis zone consists of a 9 x 9 grid cell area with the monitoring site in the 

center cell. For the Northbrook site in Chicago and the sites in Detroit and Milwaukee—where 

average morning wind speeds were lower—the grid analysis zone consists of a 7 x 7 grid cell 

area around each site. 

Additional pre-processing was required for 2005 on-road mobile and biogenic sources 

because it was necessary to use emissions data that had been prepared for the Comprehensive Air 

Quality Model with extensions (CAMx). For 2005, gridded, hourly criteria pollutant emissions 

for on-road mobile sources were available only for January, so gridded hourly emissions for July 

were developed on the basis of CAMx-ready emissions.18 The CAMx-ready files for January 

and July contain gridded, hourly emissions, but the emissions for organic species are grouped 

together by carbon bond mechanisms rather than reported by individual hydrocarbon species (as 

required for comparisons with ambient data). As a result, scaling factors were derived from the 

January and July CAMx emissions data that could be used to convert January criteria pollutant 

emissions data to July emissions data. Specifically, CAMx-ready species CO, nitric oxide (NO), 

and paraffin carbon bond (PAR19), were extracted for the grid analysis zone around each 

monitoring site; the ratio of January and July morning hour (0600–0900) emissions for each site 

was used to scale January criteria pollutant emissions that had been extracted from PostgreSQL 

files. For other months of interest, on-road emissions data were prepared by performing a linear 

interpolation on January and July emissions, in keeping with the method LADCO has used to 

develop emissions estimates for on-road sources for months other than January and July. 

For biogenic sources, CAMx-ready emission inputs were provided at a 12-km resolution 

for each day of 2005. Emissions data from these files were averaged across months of interest 

(December–February and June–August), and isoprene20 emissions for each monitoring site’s grid 

analysis were then extracted from each monthly average file. Because biogenic emissions data 

were reported at a 12-km resolution, gridded emissions were disaggregated to a 4-km resolution 

by evenly distributing the emissions for each 12-km grid cell across the nine 4-km grid cells 

contained within the larger 12-km cell. 

Once pre-processing of the emissions data was complete, STI speciated (i.e., 

disaggregated into individual hydrocarbon species) anthropogenic VOC emissions using the 

speciation profiles and cross-reference files provided by LADCO. At LADCO’s direction, the 

same speciation data was applied to both the 2005 and 2008 inventories, and this process resulted 

in a speciated inventory with hundreds of chemical species. However, the ambient data 

collection and analysis method is capable of quantifying only hydrocarbons containing between 

approximately 2 and 12 carbon atoms (i.e., PAMS hydrocarbons). To ensure that the same 

 

18 This step was unnecessary for the 2008 inventories, as gridded, hourly on-road emissions data was available for 

all months. 

19 PAR is the dominant organic species in the on-road emissions inventories and was used as a surrogate for VOC 

emissions. 

20 Isoprene is the dominant biogenic species and is the only biogenic species measured at PAMS sites. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

 2-27

chemical compounds are being compared in the ratio comparisons, the individual chemical 

species reported in the emissions inventory were matched to those measured in the ambient data. 

The compounds reported in the emissions inventory that were not measurable in the ambient 

samples were excluded from the analysis. To compare the emissions inventory data to ambient 

data, the emissions inventory data were converted from mass to molar units. 

2.2.2 Emissions Data Characterizations by Site 

To gain an understanding of the source mix around each monitoring site, we summarized 

the 2005 and 2008 emissions data for each site’s grid analysis zone. Tables 2-6 through 2-8

summarize morning (0600-0900) emissions for sites where TNMOC/NOx and CO/NOx ratios 

were evaluated, while Figures 2-20 and 2-21 break down morning emissions by source sector 

and year for all sites. These tables and figures show that, in general, CO and NOx emissions 

decreased more sharply from 2005 to 2008 than VOC emissions. This difference was largely 

driven by the on-road mobile source sector, as 2008 CO and NOx emissions from the MOVES 

model were 28% to 78% lower for winter months than corresponding 2005 estimates generated 

with MOBILE6.2, while 2008 on-road VOC emissions were comparable to (and, in some cases, 

higher) than corresponding 2005 emissions for both summer and winter months (see 

Figure 2-22). It should be noted that the sharp decreases in on-road NOx emissions around the 

monitoring sites was driven, in part, by differences in the spatial distributions of emissions for 

2005 and 2008. For example, Figure 2-23 shows the spatial distribution of on-road NOx

emissions for 2005 and 2008 for Cook County, and emissions have clearly been shifted from the 

lakefront area to the northwestern part of the county.21 However, the total on-road NOx

emissions for Cook County decreased by 32% from 2005 to 2008 (for January weekdays), so the 

significant NOx emissions reductions around the Chicago-area monitoring sites was not solely 

due to spatial differences in the 2005 and 2008 inventories. 

The 2008 inventories also show less of an emissions decrease from Saturdays to Sunday 

than the 2005 inventories, which is again driven by differences in the on-road mobile source 

sector. The 2008 MOVES-based inventories treat Saturdays and Sundays the same and also 

show less of a decrease from weekdays to weekend days than the 2005 inventories (see Figure 

2-24). However, it should be noted that this feature of the 2008 on-road emissions data results 

from using MOVES default day-of-week profiles. 

Emissions summaries by source sector for each monitoring site of interest (see 

Figures 2-20 and 2-21) show that on-road mobile source emissions account for 61% to 80% of 

the January CO emissions in both 2005 and 2008. For 2005, on-road mobile sources account for 

50% to 73% of the January and July NOx emissions around each monitoring site except for the 

Gary site, where the point source CO and NOx inventories were more dominant than at the other 

sites. However, for 2008, on-road mobile sources account for only 29% to 54% of the January 

and July NOx emissions around the non-Gary sites due to sharp reductions in on-road NOx

emissions between the 2005 and 2008 inventories. For VOC, area sources account for 35% to 

 

21 These differences in the spatial distribution of on-road NOx emissions result from the use of link-level vehicle 

activity data for the 2005 inventory vs. the gridding of county-level 2008 emissions using spatial surrogate data 

(e.g., rural secondary roads for truck activity). 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

 2-28

57% of the January and July emissions around each site in both 2005 and 2008,22 while on-road 

mobile sources account for only 15% to 39% of the January and July emissions around each site. 

For the sites where TNMOC/NOx ratios were evaluated, VOC emissions were highest 

around the Chicago-Jardine site and lowest around the Gary and Milwaukee sites for both 2005 

and 2008 (see Table 2-6). Conversely, 2005 ambient TNMOC concentrations were highest at the 

Gary and Detroit-East 7 Mile sites, and lowest at the Jardine site. In addition, VOC emissions 

around the East 7 Mile site were 18% lower than VOC emissions around the Jardine site (see 

Table 2-6). These discrepancies suggest that VOC emissions are underestimated at the Gary and 

East 7 Mile sites in the 2005 inventories. 

For 2008, weekday VOC emissions decreased by 26% at the Milwaukee site relative to 

2005, while 2008 ambient TNMOC concentrations increased by 24% relative to 2004. At the 

Chicago-Northbrook site, both VOC emissions and ambient TNMOC concentrations showed 

little change from 2005 to 2008 (Milwaukee and Northbrook were the only two sites for which 

2008 ambient TNMOC measurements were available). 

For sites where CO/NOx ratios were evaluated, 2005 and 2008 emissions were highest at 

the Franklin and Mannheim sites in Chicago and lowest at the Milwaukee site (see Tables 2-7 

and 2-8). Across all sites and years, emissions decreased more sharply relative to weekdays on 

Sundays than on Saturdays, though this effect was much more pronounced in the 2005 data than 

the 2008 data because Saturday and Sunday emissions were identical in the 2008 MOVES-based 

on-road inventory (as discussed above). 

Table 2-6. Summary of summer (July) VOC and NOx emissions for hours 0600 to 0900 

for the grid analysis zone around each monitoring site analyzed. 

VOC (tons/day) NOx (tons/day) Site 

Weekday Saturday Sunday Weekday Saturday Sunday 

2005 Data 

Chicago-Jardine 43.7 41.3 34.3 43.0 37.1 32.2 

ChicagoNorthbrook 19.0 19.9 15.9 16.6 15.1 12.7 

Milwaukee 18.3 12.2 9.7 19.5 9.9 6.0 

Gary 13.1 15.9 12.0 22.3 21.8 19.3 

Detroit-E7 Mile 35.9 25.2 18.2 29.0 13.0 9.4 

2008 Data 

Chicago-Jardine 40.2 40.5 40.3 28.0 24.5 23.9 

ChicagoNorthbrook 19.6 19.8 19.7 12.3 10.5 10.2 

Milwaukee 13.6 13.2 13.2 11.6 9.9 9.4 

Gary 11.6 13.8 13.8 17.3 17.3 16.0 

Detroit-E7 Mile 26.1 22.8 22.7 15.7 12.8 12.5 

 

22 Key area sources of VOC include architectural coatings and consumer products. 
2-29

Table 2-7. Summary of summer (July) CO and NOx emissions for hours 0600 to 0900 for the grid analysis zone ar

monitoring site analyzed. 

CO (tons/day) NOx (tons/day) Site Weekday Saturday Sunday Weekday Saturday 

2005 Data 

Chicago-Franklin 237.1 279.4 193.7 46.4 40.6 Chicago-Mannheim 324.1 386.5 254.5 56.3 49.3 Milwaukee 91.0 75.1 46.4 19.5 9.9 Detroit-Linwood 169.5 147.4 102.2 35.7 18.3 

2008 Data 

Chicago-Franklin 178.3 162.1 159.9 28.1 25.1 Chicago-Mannheim 225.0 197.0 194.4 28.1 23.8 Milwaukee 73.5 65.0 64.3 11.6 9.9 Detroit-Linwood 130.8 113.6 112.4 19.6 16.5 

Table 2-8. Summary of winter (January) CO and NOx emissions for hours 0600 to 0900 for the grid analysis zone 

monitoring site analyzed. 

CO (tons/day) NOx (tons/day

Site Weekday Saturday Sunday Weekday Saturday 

2005 Data 

Chicago-Franklin 255.9 178.5 139.9 48.2 39.4 Chicago-Mannheim 332.5 235.1 181.1 59.7 47.7 Milwaukee 152.3 40.8 42.0 23.4 7.9 Detroit-Linwood 241.6 130.9 99.1 43.8 20.4 

2008 Data 

Chicago-Franklin 181.9 144.9 143.4 30.5 26.9 Chicago-Mannheim 206.7 164.0 162.2 29.4 25.3 Milwaukee 77.6 63.0 62.5 12.3 10.7 Detroit-Linwood 123.5 101.1 100.3 21.1 18.3 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

2-30

Jardine

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Area

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Onroad

Figure 2-20. January weekday emissions by source sector for the grid analysis zone 

around each monitoring site for hours 0600 to 0900. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

2-31

Jardine

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Figure 2-21. July weekday emissions by source sector for the grid analysis zone around 

each monitoring site for hours 0600 to 0900. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

2-32

ROG - January

0

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Jardine

Northbrook

Franklin

Mannheim

Gary

East 7 Mile

Linwood

Milwaukee

Emissions (tons)

2005

2008

CO - July

0

50

100

150

200

250

300

Jardine

Northbrook

Franklin

Mannheim

Gary

East 7 Mile

Linwood

Milwaukee

Emissions (tons)

2005

2008

Figure 2-22. January (left) and July (right) weekday on-road mobile source emissions for the grid 

analysis zone around each monitoring site for hours 0600 to 0900. 
Upper Midwest Emissions Inventory Evaluation Data Acquisition and Processing 

2-33

Figure 2-23. Spatial distributions of NOx emissions from on-road mobile sources in Cook 

County for LADCO’s 2005 (left) and 2008 (right) inventories. 

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

Mon Tues Wed Thu Fri Sat Sun

Percentage of weekly emissions

2005 - Chicago

2005 - Detroit

2005 - Milwaukee

2005 - Gary

2008 - All Cities

Figure 2-24. Day-of-week emissions profiles for on-road mobile sources. 

.

Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-1

3. Pollutant Ratio Comparison Results 

To evaluate the relative amounts of TNMOC (PAMSHC), NOx, and CO in the urban 

areas of interest, ambient- and emissions inventory-derived TNMOC/NOx and CO/NOx ratios 

were compared. Comparisons were made for the full extent grid analysis zone surrounding each 

monitoring site and for each individual wind quadrant within the analysis zone. Ambient data 

average and median ratios were calculated, and ratios were calculated for the emissions 

inventory with and without elevated sources.23

3.1 TNMOC/NOx Ratio Comparisons 

TNMOC/NOx ratios for the summer months were calculated by day of week (weekday, 

Saturday, and Sunday), month (June, July, and August), summer season (June through August), 

and wind quadrant. For 2005, comparisons between ambient- and emissions-inventory-derived 

TNMOC/NOx ratios were made for five sites: Chicago-Jardine, Chicago-Northbrook, Gary, 

Detroit-East 7 Mile, and Milwaukee. For 2008, comparisons were made for the two sites for 

which ambient TNMOC measurements were available: Chicago-Northbrook and Milwaukee. 

Table 3-1 shows calculated ratios for the full grid extent around each monitoring site 

(previously shown in Table 1-2) for all summer days. For both 2005 and 2008, these data show 

good agreement24 (±20%) between ambient- and emissions inventory-derived ratios at the 

Chicago sites. However, at the remaining sites, ambient-derived ratios were higher than 

emissions inventory-derived ratios by a factor of 1.8 or more, although the ratios showed 

somewhat closer agreement when elevated sources were excluded from the analysis. 

Across all sites, emissions inventory-derived TNMOC/NOx ratios were higher in 2008 

than in 2005, which resulted from decreases in on-road NOx emissions that were greater than 

decreases in on-road VOC emissions. At the two sites for which both 2005 and 2008 data were 

available, ambient-derived TNMOC/NOx ratios were also higher in 2008 than in 2005. The 

following sections show TNMOC/NOx ratio charts by wind quadrant and day of week and 

discuss the results of the analysis for each site. Additional charts (e.g., TNMOC/NOx ratios by 

month) can be found in Appendix D. 

 

23 Emissions from elevated sources may be injected above the mixed layer and, hence, may not affect surface-level 

ambient concentrations—especially during morning hours. Pollutant ratios were calculated with and without 

elevated sources to characterize the potential effects of this phenomenon. 

24 Because of the inherent uncertainties associated with this analysis method, ambient- and emissions inventoryderived ratios that are within approximately 25-50% of each other are considered to be in good agreement 

(California Air Resources Board, 1997). 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-2

Table 3-1. TNMOC/NOx ratios by site for the hours 0600 to 0900 (emission ratios for full 

grid extent around each site; ambient ratios for 2005 based on 2004–2006 data).

Emissions Inventory Ratios

Site Ambient 

Ratios Low Level 

Only 

Low Level 

+ Elevated 

Ambient/EI 

(Low Level) 

Ambient/EI 

(Low Level 

+ Elevated) 

2005 Data 

Chicago-Jardine 1.6 1.7 1.6 0.9 1.0 

Chicago-Northbrook 2.2 1.8 1.8 1.2 1.2 

Gary 6.0 1.6 1.1 3.6 5.4 

Detroit-E7 Mile 6.3 2.3 2.2 2.7 2.9 

Milwaukee 3.5 2.0 1.5 1.8 2.3 

2008 Data 

Chicago-Jardine -- 2.5 2.2 -- -- 

Chicago-Northbrook 2.6 2.9 2.9 0.9 0.9 

Gary -- 1.8 1.1 -- -- 

Detroit-E7 Mile -- 2.7 2.4 -- -- 

Milwaukee 5.1 2.1 1.7 2.4 2.9 

3.1.1 Ratio Comparison Results for Chicago-Jardine 

Figure 3-1 shows 2005 TNMOC/NOx ratios by wind quadrant25 and day of week for the 

Jardine site in Chicago, Illinois. Overall, there is good agreement between the ambient- and 

emissions inventory-derived ratios at this site across all wind quadrants and days of week. For 

wind quadrant 1, however, the agreement between ambient- and emissions inventory-derived 

ratios is poorer than for the remaining wind quadrants, with the emissions inventory-derived ratio 

about 40% higher than the ambient-derived ratio. However, it should be noted that because wind 

quadrant 1 lies northeast of the site, over Lake Michigan (see Figure 2-4), emission levels in that 

quadrant are very low compared to the other wind quadrants. 

Also, the agreement between ambient- and emissions inventory-derived TNMOC/NOx

ratios is poorer on weekend days than on weekdays. This is particularly true for Sundays, when 

the ambient-derived TNMOC/NOx ratio is about 40% higher than the corresponding 

emissions-derived ratio. Sunday TNMOC and NOx concentrations at Jardine are both about 20% 

higher than Saturday concentrations, making the ambient-derived TNMOC/NOx ratios at that site 

virtually the same on Saturdays and Sundays. However, the emissions inventory shows 

decreases in both VOC and NOx emissions on Sundays relative to Saturdays, and the somewhat 

sharper decrease in VOC emissions lowers the emissions inventory-derived TNMOC/NOx ratio. 

 

25 On all bar charts, the ambient value represents the median, and error bars represent the 25th and 75th percentiles. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-3

0

1

2

3

4

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Wind Quadrant

TNMOC/NOx Ratio 

0

1

2

3

4

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.6

0.9

0.9

0.8 0.9 0.9

1.3 1.4

0

1

2

3

4

1234

Wind Quadrant

TNMOC/NOx Ratio 

0

1

2

3

4

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.6

0.9

0.9

0.8 0.9 0.9

1.3 1.4

Figure 3-1. TNMOC/NOx ratios by wind quadrant and day of week for the Jardine site, 

2004-2006 (note that for this figure and subsequent ratio comparison figures, values above each 

ratio group represent the ambient ratio divided by the low-level emissions only ratio). 

3.1.2 Ratio Comparison Results for Chicago-Northbrook 

Figure 3-2 shows 2005 TNMOC/NOx ratios by wind quadrant and day of week for the 

Northbrook site in Chicago, Illinois. Generally, there is good agreement between the 

ambient- and emissions inventory-derived ratios at this site; however, the agreement between 

ambient- and emissions inventory-derived ratios is poorer for wind quadrants 1 and 3 than for the 

remaining wind quadrants. Much of wind quadrant 1 lies over Lake Michigan (see Figure 2-5), 

and emission levels are thus relatively low in that quadrant. For wind quadrant 3, NOx emission 

levels are 40% higher than in neighboring wind quadrant 2, while VOC emission levels are 

virtually identical for those two wind quadrants. These higher NOx emissions in wind quadrant 3 

are driven by heavy-duty mobile source emissions, suggesting that emissions from this source 

may be overestimated in wind quadrant 3. 

0

1

2

3

4

5

1234

Wind Quadrant

TNMOC/NOx Ratio 

0

1

2

3

4

5

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.6

1.1 1.8 1.4

1.2 1.3

1.4

2.0

0

1

2

3

4

5

1234

Wind Quadrant

TNMOC/NOx Ratio 

0

1

2

3

4

5

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.6

1.1 1.8 1.4

1.2 1.3

1.4

2.0

Figure 3-2. TNMOC/NOx ratios by wind quadrant and day of week for the Northbrook site, 2004–2006. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-4

The ambient-derived TNMOC/NOx ratio for Sundays is a factor of 2 higher than the 

emissions inventory-derived ratio for Sundays at the Northbrook site, whereas the ambientderived ratio for weekdays and Saturdays are only about 30% higher than the emissions 

inventory-derived ratios. Because TNMOC concentrations are higher (by about 10%) and NOx

concentrations are lower (by about 30%) on Sundays than on Saturdays, the ambient-derived 

TNMOC/NOx ratio is higher on Sundays than on Saturdays. However, the emissions 

inventory-derived ratios do not capture this trend, as both VOC26 and NOx emissions decrease on 

Sundays relative to Saturdays, with VOC decreasing somewhat more sharply and lowering the 

emissions inventory-derived TNMOC/NOx ratio. 

Ambient- and emissions inventory-derived TNMOC/NOx ratios for the Northbrook site 

were also prepared using 2008 data (see Figure 3-3), and the overall (all days and wind 

quadrants) ambient-derived TNMOC/NOx ratio for this site increased from 2.2 in 2004–2006 to 

2.6 in 2008 (an 18% increase). This higher 2008 ratio reflects the increasing TNMOC 

concentrations and decreasing NOx concentrations at this site (see Section 2.1.4). The emissions 

data for Northbrook showed a small VOC increase from 2005 to 2008 and a large NOx decrease. 

As a result, the emissions inventory-derived TNMOC/NOx ratio increased by 61%, and the 

ambient- and emissions inventory-derived ratios showed somewhat closer agreement for 2008 

than for 2005. 

It should also be noted that, when examined by day of week and wind quadrant, the 2008 

TNMOC/NOx ratios show a sharper increase relative to 2004–2006 ratios in wind quadrants 1 

and 4 and on weekdays.27. These results suggest that the increase in TNMOC emissions around 

this site between 2004–2006 and 2008 largely came from the area north of the site. 

0

1

2

3

4

5

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0

1

2

3

4

5

1234

Wind Quadrant

TNMOC/NOx Ratio 

1.1

1.0 1.1

1.0 1.0

1.1

1.1 1.1

0

1

2

3

4

5

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0

1

2

3

4

5

1234

Wind Quadrant

TNMOC/NOx Ratio 

1.1

1.0 1.1

1.0 1.0

1.1

1.1 1.1

Figure 3-3. TNMOC/NOx ratios by wind quadrant and day of week for the Northbrook site, 2008. 

 

26 The organic species in the ambient data are referred to as TNMOC and in the emissions inventory as VOC. For 

simplicity, all hydrocarbon-to-NOx ratios are referred to as “TNMOC/NOx.” 27 For analyses involving 2008 data, Saturdays and Sundays were grouped together as weekend days because of the 

relatively small number of Saturday/Sunday samples. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-5

3.1.3 Ratio Comparison Results for Gary 

Figure 3-4 shows 2005 TNMOC/NOx ratios by wind quadrant and day of week for the 

Gary, Indiana, site. Agreement between ambient- and emissions inventory-derived 

TNMOC/NOx ratios is poor at the Gary site, with the ambient-derived ratios 3.4 to 5.0 times 

higher than the emissions-based ratios across all wind quadrants and days of week. This 

discrepancy may largely be driven by an underestimate of VOC emissions around the Gary site 

(see Section 2.2.2), which is near several large industrial sources—including the Burns Harbor 

Steel Plant. Among days of the week, agreement between ambient- and emissions inventoryderived TNMOC/NOx ratios is poorest on Sundays, as the 40% decrease in ambient NOx

concentrations between Saturdays and Sundays is not reflected in the emissions data. 

0

5

10

15

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Wind Quadrant

TNMOC/NOx Ratio 

0

5

10

15

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

3.5 3.5 3.8 4.6 3.6 3.9 3.4

5.0

0

5

10

15

1234

Wind Quadrant

TNMOC/NOx Ratio 

0

5

10

15

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

3.5 3.5 3.8 4.6 3.6 3.9 3.4

5.0

Figure 3-4. TNMOC/NOx ratios by wind quadrant and day of week for the Gary site, 2004–2006. 

3.1.4 Ratio Comparison Results for Detroit-East 7 Mile 

Figure 3-5 shows the 2005 TNMOC/NOx ratios by wind quadrant and day of week for 

the East 7 Mile site in Detroit, Michigan. Agreement between ambient- and emissions 

inventory-derived TNMOC/NOx ratios is poor at the East 7 Mile site, with the ambient-derived 

ratios 2.5 to 4.0 times higher than the emissions-based ratios across all wind quadrants and days 

of week. Ambient-derived TNMOC/NOx ratios are lowest when winds are from wind quadrant 

3, reflecting the impact of large industrial sources of NOx southwest of this site (Brown, 2006). 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-6

0

5

10

15

1234

Wind Quadrant

TNMOC/NOx Ratio 

0

5

10

15

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

2.7 4.0

2.5 2.6 2.7 3.4

2.6 3.4

0

5

10

15

1234

Wind Quadrant

TNMOC/NOx Ratio 

0

5

10

15

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

2.7 4.0

2.5 2.6 2.7 3.4

2.6 3.4

Figure 3-5. TNMOC/NOx ratios by wind quadrant and day of week for the East 7 Mile site, 2004–2006. 

Ambient TNMOC concentrations are highest at the East 7 Mile site among all sites, 

although VOC emissions levels around the East 7 Mile site are 18% lower than they are around 

the Chicago-Jardine site (see Table 2-6). This discrepancy suggests that VOC emissions are 

underestimated around the East 7 Mile site. 

3.1.5 Ratio Comparison Results for Milwaukee 

Figure 3-6 shows the 2005 TNMOC/NOx ratios by wind quadrant and day of week for 

the Milwaukee, Wisconsin, site. Agreement between ambient- and emissions inventory-derived 

TNMOC/NOx ratios is mediocre at the Milwaukee site, with the ambient-derived ratios 1.5 to 2.2 

times higher than the emissions-based ratios across all wind quadrants and days of week. 

Milwaukee was the only site where agreement between ambient- and emissions inventoryderived TNMOC/NOx ratios was better on Sundays than on weekdays or Saturdays, as 

Milwaukee was the only site with lower TNMOC concentrations on Sundays than on Saturdays 

(reflected in the VOC emissions levels for the site). 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-7

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1

2

3

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6

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TNMOC/NOx Ratio 

0

2

4

6

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

1.7 2.0

1.9

1.7 1.8 2.2 1.9 1.5

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1

2

3

4

5

6

1234

Wind Quadrant

TNMOC/NOx Ratio 

0

2

4

6

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

1.7 2.0

1.9

1.7 1.8 2.2 1.9 1.5

Figure 3-6. TNMOC/NOx ratios by wind quadrant and day of week for the Milwaukee site, 2004–2006. 

Ambient- and emissions inventory-derived TNMOC/NOx ratios for the Milwaukee site 

were also prepared using 2008 data (see Figure 3-7), and the overall (all days and wind 

quadrants) ambient TNMOC/NOx ratio for this site increased from 3.5 in 2004–2006 to 5.1 in 

2008 (a 46% increase). This higher 2008 ratio reflects the increasing TNMOC concentrations 

and decreasing NOx concentrations at this site (see Section 2.1.4). The emissions data for 

Milwaukee showed significant decreases in both VOC and NOx emissions from 2005 to 2008, 

and emissions-inventory derived TNMOC/NOx ratios were slightly higher for 2008 than for 

2005. As a result, the ambient- and emissions inventory-derived ratios showed poorer agreement 

for 2008 than for 2005. 

 

0

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4

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8

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TNMOC/NOx Ratio 

0

2

4

6

8

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

3.4 2.8 2.7 2.5

2.6 2.7 3.1 3.1

0

2

4

6

8

1234

Wind Quadrant

TNMOC/NOx Ratio 

0

2

4

6

8

All WD SAT SUN

Day of Week

TNMOC/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

3.4 2.8 2.7 2.5

2.6 2.7 3.1 3.1

Figure 3-7. TNMOC/NOx ratios by wind quadrant and day of week for the Milwaukee site, 2008. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-8

3.2 CO/NOx Ratio Comparisons 

CO/NOx ratios were calculated by day of week, month, and season. For 2005, 

comparisons between ambient- and emissions inventory-derived CO/NOx ratios were made for 

four sites: Chicago-Mannheim, Chicago-Franklin, Detroit-Linwood, and Milwaukee. Also, 

CO/NOx ratios were calculated by wind quadrant at the Milwaukee and Chicago-Mannheim 

sites28. For 2008, comparisons were made for the three sites for which ambient CO 

measurements were available: the Mannheim, Franklin, and Northbrook sites in Chicago (and 

emissions inventory-derived ratios were calculated for the remaining sites as well). 

Table 3-2 shows calculated ratios for the full grid extent around each monitoring site for 

all summer and winter days. For 2005, these calculations show that ambient- and emissions 

inventory-derived ratios agree within ±30% at all sites. Agreement is generally closer for winter 

months when CO concentrations are much higher than in summer months, and agreement is also 

generally closer when elevated sources are excluded from the calculations. For 2008, ambientderived CO/NOx ratios at the Mannheim and Franklin sites were 5% to 39% lower than for 2005; 

however, emissions inventory-derived CO/NOx ratios increased by up to 35% at those sites. As 

a result, the ambient- and emissions-inventory derived ratios show poorer agreement for 2008 

than for 2005. 

The following sections show CO/NOx ratio charts by wind quadrant and day of week and 

discuss the results of the analysis for each site. Additional charts (e.g., CO/NOx ratios by wind 

quadrant) can be found in Appendix D.

 

28 The meteorological data needed to support this analysis are not available at the other sites. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-9 

Table 3-2. CO/NOx ratios by site (emission ratios for full grid extent around each site; 

ambient ratios for 2005 based on 2004–2006 data). 

Emissions Inventory 

Ratios 

Site Season Ambient 

Ratios Low Level 

Only 

Low Level 

+ Elevated 

Ambient/EI 

(Low 

Level) 

Ambient/EI 

(Low Level 

+ Elevated)

2005 Data 

Winter 6.4 8.2 8.2 0.8 0.8 ChicagoMannheim Summer 8.2 11.2 11.2 0.7 0.7 

Winter 7.3 8.0 7.6 0.9 1.0 ChicagoFranklin Summer 8.6 10.9 10.3 0.8 0.8 

Winter 9.9 10.1 8.0 1.0 1.2 Linwood 

(Detroit) Summer 12.5 11.6 9.1 1.1 1.4 

Winter 10.0 11.2 8.9 0.9 1.1 

Milwaukee 

Summer 13.6 11.9 9.3 1.2 1.5 

2008 Data 

Winter 4.2 11.1 10.9 0.4 0.4 ChicagoMannheim Summer 5.0 15.0 13.6 0.3 0.4 

Winter 5.9 9.6 9.2 0.6 0.6 ChicagoFranklin Summer 8.2 11.6 10.3 0.7 0.8 

Winter 8.6 11.9 11.9 0.7 0.7 ChicagoNorthbrook Summer 16.7 16.0 16.0 1.0 1.0 

Winter -- 11.5 9.2 -- -- Linwood 

(Detroit) Summer -- 12.7 9.5 -- -- 

Winter -- 11.3 9.8 -- -- 

Milwaukee 

Summer -- 12.0 9.8 -- -- 

3.2.1 Ratio Comparison Results for Chicago-Mannheim 

Figure 3-8 shows 2005 CO/NOx ratios by season, wind quadrant, and day of week for the 

Mannheim site in Chicago, Illinois. Overall, there is good agreement between the ambient- and 

emissions inventory-derived ratios at this site across all wind quadrants and days of week. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-10 

However, there is poorer agreement between ambient- and emissions inventory-derived CO/NOx

ratios on Sundays than on weekdays or Saturdays, as the magnitude of the decrease in NOx

concentrations from Saturdays to Sundays is not completely reflected in the emissions data. 

 

0

5

10

15

20

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0

5

10

15

20

1234

Wind Quadrant

CO/NOx Ratio 

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CO/NOx Ratio 

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Ambient

EI - Low Level Only

EI - With Elevated

Source

0.8 0.8 0.8 0.8 0.8 0.6 0.9 1.4

0.9 0.6 0.7 0.6 0.7 0.7

0.8 1.5

0

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CO/NOx Ratio 

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Ambient

EI - Low Level Only

EI - With Elevated

Source

0.8 0.8 0.8 0.8 0.8 0.6 0.9 1.4

0

5

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1234

Wind Quadrant

CO/NOx Ratio 

0

5

10

15

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All WD SAT SUN

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CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.8 0.8 0.8 0.8 0.8 0.6 0.9 1.4

0.9 0.6 0.7 0.6 0.7 0.7

0.8 1.5

Figure 3-8. CO/NOx ratios by season (top is winter and bottom is summer), wind 

quadrant, and day of week for the Chicago-Mannheim site, 2004–2006. 

Ambient- and emissions inventory-derived CO/NOx ratios for the Mannheim site were 

also prepared using 2008 data (see Figure 3-9), and for ambient data, the overall (all days and 

wind quadrants) wintertime CO/NOx ratio for this site decreased from 6.4 in 2004–2006 to 4.2 in 

2008 (a 34% decrease). This lower 2008 ratio reflects the decreasing CO concentrations at this 

site (see Section 2.1.4). However, the wintertime emissions inventory-derived CO/NOx ratios for 

this site increased by 35% from 2005 to 2008; as a result, the agreement between ambient- and 

emissions inventory-derived CO/NOx ratios is much poorer for 2008 than for 2005. Because 

2005 to 2008 reductions in CO emissions are similar to reductions in CO concentrations (both 

around 40%) while NOx emission reductions (50%) are much larger than NOx concentration 

reductions (13%), this discrepancy indicates that NOx reductions from 2005 to 2008 in the 

emissions inventory are too large. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-11 

It should also be noted that the ambient-derived CO/NOx ratios for 2008 increase on 

weekend days, as was the case with the ratios calculated from 2004–2006 ambient data. 

However, the 2008 emissions inventory-derived CO/NOx ratios show little variation from 

weekdays to weekend days (see Figure 3-9). 

0

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CO/NOx Ratio 

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CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.4 0.3 0.3 0.3 0.4 0.3 0.5 0.5

0

5

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1234

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CO/NOx Ratio 

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5

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EI - With Elevated

Source

0.4

0.3

0.3

0.3 0.3 0.3 0.5 0.4

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1234

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CO/NOx Ratio 

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EI - With Elevated

Source

0.4 0.3 0.3 0.3 0.4 0.3 0.5 0.5

0

5

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1234

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CO/NOx Ratio 

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Ambient

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EI - With Elevated

Source

0.4

0.3

0.3

0.3 0.3 0.3 0.5 0.4

Figure 3-9. CO/NOx ratios by season (top is winter and bottom is summer), wind 

quadrant, and day of week for the Chicago-Mannheim site, 2008. 

3.2.2 Ratio Comparison Results for Chicago-Franklin 

Figure 3-10 shows 2005 CO/NOx ratios by season and day of week29 for the Franklin site 

in Chicago, Illinois. Overall, there is good agreement between the ambient- and emissions 

inventory-derived ratios at this site across all days of week. However, there is poorer agreement 

between ambient- and emissions inventory-derived CO/NOx ratios on Sundays than on weekdays 

or Saturdays, as the magnitude of the decrease in NOx concentrations from Saturdays to Sundays 

is not completely reflected in the emissions data. 

 

29 Pollutant ratios by wind quadrant could not be calculated for the Franklin site because of a lack of wind data. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-12 

0

2

4

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8

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12

14

16

18

All WD SAT SUN

Day of Week

CO/NOx Ratio 

0.9 0.7 1.0

1.6

0

2

4

6

8

10

12

14

16

18

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.8 0.8

0.9 1.3

0

2

4

6

8

10

12

14

16

18

All WD SAT SUN

Day of Week

CO/NOx Ratio 

0.9 0.7 1.0

1.6

0

2

4

6

8

10

12

14

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18

All WD SAT SUN

Day of Week

CO/NOx Ratio 

0.9 0.7 1.0

1.6

0

2

4

6

8

10

12

14

16

18

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.8 0.8

0.9 1.3

Figure 3-10. CO/NOx ratios by season (left is winter and right is summer) and by day of 

week for the Chicago-Franklin site, 2004–2006. 

Ambient- and emissions inventory-derived CO/NOx ratios for the Franklin site were also 

prepared using 2008 data (see Figure 3-11); for ambient data, the overall (all days and wind 

quadrants) wintertime CO/NOx ratio for this site decreased from 7.3 in 2004–2006 to 5.9 in 2008 

(a 19% decrease). This lower 2008 ratio reflects the decreasing CO concentrations at this site 

(see Section 2.1.4). However, the wintertime emissions inventory-derived CO/NOx ratios for 

this site increased by 20% from 2005 to 2008; as a result, the agreement between ambient- and 

emissions inventory-derived CO/NOx ratios is generally poorer for 2008 than for 2005. 

Although 2005 to 2008 reductions in CO emissions are similar to reductions in CO 

concentrations (both around 25%), reductions in NOx emissions (37%) are much larger than 

reductions in NOx concentrations (6%). This discrepancy indicates that NOx reductions from 

2005 to 2008 in the emissions inventory are too large. 

0

2

4

6

8

10

12

14

All WD SAT SUN

Day of Week

CO/NOx Ratio 

0.6 0.5 0.9 0.9

0

5

10

15

20

25

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.7 0.6

1.3 1.3

0

2

4

6

8

10

12

14

All WD SAT SUN

Day of Week

CO/NOx Ratio 

0.6 0.5 0.9 0.9

0

5

10

15

20

25

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.7 0.6

1.3 1.3

Figure 3-11. CO/NOx ratios by season (left is winter and right is summer) and by day of 

week for the Chicago-Franklin site, 2008. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-13 

It should be noted that CO/NOx ratios calculated for Sundays are an exception to the 

trend described above, as emissions inventory-derived ratios show closer agreement with 

ambient-derived ratios for 2008 than for 2005, particularly for winter months (see Figure 3-11). 

This occurs, in part, because ambient-derived CO/NOx ratios for 2008 do not increase sharply 

from Saturdays to Sundays, as was the case with the ratios for 2005. 

3.2.3 Ratio Comparison Results for Chicago-Northbrook 

Figure 3-12 shows 2008 CO/NOx ratios by season, wind quadrant, and day of week for 

the Northbrook site in Chicago, Illinois (no ambient CO measurements were available for this 

site from 2004–2006). Generally, the ambient- and emissions inventory-derived ratios at this site 

show good agreement (±50%) across all wind quadrants and days of week. However, the 

ambient- and emissions inventory-derived CO/NOx ratios show poorer agreement on weekend 

days than on weekdays, particularly during summer months. During both winter and summer 

months, the ambient-derived CO/NOx ratios increase sharply on weekend days compared to 

weekdays, while the emissions inventory-derived ratios remain relatively constant from 

weekdays to weekend days. Although weekday to weekend reductions in CO emissions are 

similar to reductions in CO concentrations (both around 25% for winter months), NOx emission 

reductions (14% for winter months) are much smaller than NOx concentration reductions (72% 

for winter months). This discrepancy indicates that NOx reductions from weekdays to weekend 

days in the emissions inventory are too small. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-14 

0

2

4

6

8

10

12

14

16

18

20

1234

Wind Quadrant

CO/NOx Ratio 

0

5

10

15

20

25

30

35

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.7

0.7 0.8 0.6

0.7 0.6 1.5 1.4

0

5

10

15

20

25

30

35

40

1234

Wind Quadrant

CO/NOx Ratio 

0

5

10

15

20

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30

35

40

45

50

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

1.2 0.9 1.0 1.5

1.0 0.9

1.6 1.6

0

2

4

6

8

10

12

14

16

18

20

1234

Wind Quadrant

CO/NOx Ratio 

0

5

10

15

20

25

30

35

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.7

0.7 0.8 0.6

0.7 0.6 1.5 1.4

0

5

10

15

20

25

30

35

40

1234

Wind Quadrant

CO/NOx Ratio 

0

5

10

15

20

25

30

35

40

45

50

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

1.2 0.9 1.0 1.5

1.0 0.9

1.6 1.6

Figure 3-12. CO/NOx ratios by season (top is winter and bottom is summer), wind 

quadrant, and day of week for the Chicago-Northbrook site, 2008. 

3.2.4 Ratio Comparison Results for Detroit-Linwood 

Figure 3-13 shows CO/NOx ratios by season and day of week30 for the Linwood site in 

Detroit, Michigan. Overall, there is good agreement between the ambient- and emissions 

inventory-derived ratios at this site across all days of week, particularly during winter months. 

 

30 Pollutant ratios by wind quadrant could not be calculated for the Linwood site because of a lack of wind data. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-15 

0

5

10

15

20

25

30

All WD SAT SUN

Day of Week

CO/NOx Ratio 

1.0 1.0 0.9 1.0

0

5

10

15

20

25

30

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

1.1 1.4 0.8

1.3

0

5

10

15

20

25

30

All WD SAT SUN

Day of Week

CO/NOx Ratio 

1.0 1.0 0.9 1.0

0

5

10

15

20

25

30

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

1.1 1.4 0.8

1.3

Figure 3-13. CO/NOx ratios by season (left is winter and right is summer) and by day of 

week for the Detroit-Linwood site, 2004–2006. 

3.2.5 Ratio Comparison Results for Milwaukee 

Figure 3-14 shows CO/NOx ratios by season, wind quadrant, and day of week for the 

Milwaukee site in Wisconsin. Overall, there is good agreement between the ambient- and 

emissions inventory-derived ratios at this site across all wind quadrants and days of week for 

both winter and summer months. 
Upper Midwest Emissions Inventory Evaluation Pollutant Ratio Comparisons 

3-16 

0

5

10

15

20

25

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0

5

10

15

20

25

1234

Wind Quadrant

CO/NOx Ratio 

0.8 1.3

1.3 1.2

0

5

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Wind Quadrant

CO/NOx Ratio 

0

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20

25

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.8 0.9 0.8 1.0 0.9 0.8 1.1 1.1

1.2 1.5 1.0 1.0

0

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Day of Week

CO/NOx Ratio 

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EI - Low Level Only

EI - With Elevated

Source

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1234

Wind Quadrant

CO/NOx Ratio 

0.8 1.3

1.3 1.2

0

5

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Wind Quadrant

CO/NOx Ratio 

0

5

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15

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All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.8 0.9 0.8 1.0 0.9 0.8 1.1 1.1

0

5

10

15

20

25

1234

Wind Quadrant

CO/NOx Ratio 

0

5

10

15

20

25

All WD SAT SUN

Day of Week

CO/NOx Ratio 

Ambient

EI - Low Level Only

EI - With Elevated

Source

0.8 0.9 0.8 1.0 0.9 0.8 1.1 1.1

1.2 1.5 1.0 1.0

Figure 3-14. CO/NOx ratios by season (top is winter and bottom is summer), wind 

quadrant, and day of week for the Milwaukee site, 2004–2006. 
Upper Midwest Emissions Inventory Evaluation Hydrocarbon Composition Comparisons 

4-1 

4. Hydrocarbon Composition Comparison Results 

Comparisons of ambient- and emissions inventory-derived hydrocarbon compositions 

were based on the 55 individual species that were detected and identified by the ambient 

measurement systems. In addition, STI also computed and compared the relative reactivity of 

the organic species in the emissions inventory and ambient data. The reactivity of each species 

was estimated according to published MIR values that represent the ozone formation potential of 

various organic compounds (Carter, 2003). 

4.1 Relative Hydrocarbon Composition Comparisons 

Relative hydrocarbon composition comparisons were performed by day of week, season, 

and wind quadrant. For 2005, hydrocarbon composition comparisons were performed for five 

sites: Chicago-Jardine, Chicago-Northbrook, Gary, Detroit-East 7 Mile, and Milwaukee. For 

2008, comparisons were made for the two sites for which ambient TNMOC measurements were 

available: Chicago-Northbrook and Milwaukee.31 Figures 4-1 through 4-5 show comparisons 

of the ambient- and emissions inventory-derived relative compositions of 15 of the most 

abundant species in the ambient data. These hydrocarbon composition plots show that: 

 The speciation of the emissions inventory is representative of the TNMOC composition 

detected by ambient monitoring sites for some species groups, including C4+ alkanes, 

C8+ aromatics, styrenes, and propylene. 

 The speciation of the emissions inventory is representative of the TNMOC composition 

detected by ambient monitoring sites for C6+ alkanes at the Chicago and Milwaukee 

sites; however, this species is overestimated in the emissions inventory at the Gary and 

Detroit sites. C6+ alkanes are present in gasoline exhaust and evaporative emissions. 

 The speciation of the emissions inventory tends to overestimate the contribution of 

acetylene, ethylene, toluene, and isoprene compared to the ambient data. Isoprene is 

highly reactive and short-lived in the atmosphere, and therefore it may be 

under-represented in the ambient data. The dominant source of acetylene and toluene32 in 

the summer emissions inventory is gas-powered lawn and garden equipment, and the 

contribution of these species to overall hydrocarbon emissions increases on weekends, 

when lawn and garden equipment are most active (see day of week plots in Appendix E). 

The speciation profile assigned to this source in the LADCO inventories is based on a 

1997 study on emissions from four-stroke lawn mower emissions covering ten mowers 

with two types of gasoline (Battye and Harris, 2005), and the same profile is assigned to 

lawn and garden equipment in the latest version of EPA’s SPECIATE database (U.S. 

Environmental Protection Agency, 2008). Commercial aircraft are the dominant source 

of ethylene in the LADCO emissions data. A 1984 EPA speciation profile for turbine 

engine exhaust is assigned to this source category in the LADCO inventories. 

 

31 Per LADCO’s instructions, the same speciation profiles were assigned to both the 2005 and 2008 inventories, so 

the speciation of the emissions data did not change from year to year. The hydrocarbon composition of the ambient 

data also showed little year-to-year variation. 

32 For the Gary site, petroleum storage evaporative losses are another significant source of toluene. This is not true 

at the other sites. 
Upper Midwest Emissions Inventory Evaluation Hydrocarbon Composition Comparisons 

4-2 

 Compared to the ambient data, the speciation of the emissions inventory overestimates 

the contribution of pentanes at some sites, especially Detroit East 7 Mile. At the Detroit 

site, surface coating solvents are the dominant source of pentane emissions. 

 The speciation of the emissions inventory underestimates the contribution of ethane, 

propane, and C6-C11 alkanes at all sites and butane at the Chicago sites. However, 

ethane and propane are long-lived in the atmosphere and tend to accumulate; therefore, it 

is likely that the ambient monitors detected aged ethane and propane emissions. 

0%

5%

10%

15%

20%

25%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure 4-1. Comparison of 0600–0900 ambient- and emissions inventory-derived 

TNMOC compositions for the Chicago-Jardine site. 

0%

5%

10%

15%

20%

25%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient 2005

Ambient 2008

Emissions

Figure 4-2. Comparison of 0600–0900 ambient- and emissions inventory-derived 

TNMOC compositions for the Chicago-Northbrook site. 
Upper Midwest Emissions Inventory Evaluation Hydrocarbon Composition Comparisons 

4-3 

0%

5%

10%

15%

20%

25%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure 4-3. Comparison of 0600–0900 ambient- and emissions inventory-derived 

TNMOC compositions for the Gary site. 

0%

5%

10%

15%

20%

25%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure 4-4. Comparison of 0600–0900 ambient- and emissions inventory-derived 

TNMOC compositions for the Detroit-East 7 Mile site. 
Upper Midwest Emissions Inventory Evaluation Hydrocarbon Composition Comparisons 

4-4 

0%

5%

10%

15%

20%

25%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient 2005

Ambient 2008

Emissions

Figure 4-5. Comparison of 0600–0900 ambient- and emissions inventory-derived 

TNMOC compositions for the Milwaukee site. 

4.2 Hydrocarbon Reactivity Comparisons 

Hydrocarbon reactivity comparisons were performed by day of week, month, season, and 

wind quadrant for five sites using 2004–2006 ambient data and 2005 emissions data:33 ChicagoJardine, Chicago-Northbrook, Gary, Detroit-East 7 Mile, and Milwaukee. Across all sites, the 

overall weighted reactivity values for the emissions inventory for the summer season are 16% to 

80% higher than the weighted reactivity values for the ambient data. The ambient- and 

emissions inventory-derived reactivity values show the closest agreement at the Milwaukee site 

and the greatest disparity at the Northbrook site. The emissions inventory-derived reactivity 

values are consistently higher for Saturday and Sunday emissions data than for weekday 

emissions data, while the ambient-derived reactivity values show little change across days of the 

week. Tables 4-1 and 4-2 show reactivity data for the five sites. 

The hydrocarbon composition analysis in the previous section showed that the emissions 

inventory and the ambient data differ significantly between several species or group of species. 

At all sites, ethane and propane make up a higher percentage of the TNMOC concentration in the 

ambient data than in the emissions inventory, while the more reactive ethylene and acetylene 

make up a higher percentage in the emissions inventory. (Ethane and propane have MIR values 

of 0.3 and 0.6, respectively, while ethylene and acetylene are far more reactive, with MIR values 

of 9.1 and 1.2, respectively.) These differences result in higher weighted reactivity values for the 

emissions data than for the ambient data. 

 

33 These analyses were not repeated for 2008 because the 2008 hydrocarbon compositions were very similar to the 

2005 versions for both the ambient and emissions data. 
4-5

Table 4-1. Reactivity values by site, day of week, month, and season. 

Overall Weekday Saturday 

Site 

Name Month Emissions 

Inventory Ambient Emissions Inventory Ambient Emissions Inventory Ambient Emissi

Invent

June 3.9 2.8 3.7 2.8 4.0 3.0 4.0 

July 3.9 2.7 3.7 2.7 4.0 2.9 3.9 

August 3.7 2.7 3.6 2.6 3.8 2.8 3.8 

ChicagoJardine 

Summer 3.8 2.7 3.7 2.7 3.9 2.9 3.9 

June 4.5 2.5 4.3 2.5 4.5 2.4 4.6 

July 4.4 2.5 4.3 2.6 4.5 2.5 4.5 

August 4.4 2.5 4.1 2.5 4.3 2.4 4.3 

ChicagoNorthbrook 

Summer 4.5 2.5 4.2 2.5 4.4 2.5 4.4 

June 4.5 3.3 4.2 2.6 4.3 2.5 4.7 

July 4.5 3.3 4.2 2.8 4.3 2.9 4.7 

August 4.3 3.2 4.0 2.8 4.1 2.8 4.4 

Gary 

Summer 4.3 2.8 4.0 2.7 4.2 2.7 4.5 

June 3.7 2.5 3.4 2.5 3.9 2.5 4.0 

July 3.7 2.5 3.4 2.6 3.8 2.5 4.0 

August 3.5 2.5 3.3 2.6 3.7 2.5 3.8 

DetroitE7Mile 

Summer 3.6 2.5 3.4 2.6 3.8 2.5 3.9 

June 3.7 3.1 3.4 3.1 3.8 3.0 3.9 

July 3.7 3.0 3.4 2.9 3.8 2.9 3.9 

August 3.6 3.1 3.4 3.0 3.7 3.0 3.7 

Milwaukee 

Summer 3.6 3.1 3.4 3.0 3.8 3.0 3.8 
4-6

Table 4-2. Reactivity values by wind quadrant (all summer months included). 

WQ1 WQ2 WQ3 WQ

Site 

Name Emissions 

Inventory Ambient Emissions Inventory Ambient Emissions Inventory Ambient Emissions Inventory 

ChicagoJardine 3.9 2.7 3.7 2.7 3.9 2.8 3.8 ChicagoNorthbrook 4.2 2.5 3.9 2.6 4.6 2.5 4.6 Gary 4.4 2.8 4.3 2.8 4.1 2.7 3.9 DetroitE7Mile 3.4 2.7 3.5 2.5 3.7 2.5 3.8 Milwaukee 3.5 3.0 3.5 3.1 3.7 3.1 3.6 
Upper Midwest Emissions Inventory Evaluation Findings and Recommendations 

5-1

5. Findings and Recommendations 

The on-road mobile source component of LADCO’s 2005 emissions inventory was 

developed using EPA’s MOBILE6.2 model and link-level activity data. The top-down 

evaluation for the 2005 emissions inventory indicates that, in general, on-road mobile sources are 

represented accurately in the emissions data. This conclusion is based on the fact that agreement 

between ambient- and emissions-inventory-derived pollutant ratios was closest (±20%) for 

wintertime CO/NOx ratios, and on-road mobile sources accounted for 57% to 80% of wintertime 

CO and NOx emissions at all sites for which ratios were calculated. For sites in the Chicago 

area, agreement between ambient- and emissions inventory-derived pollutant ratios was as close 

as could be expected, given the limitations of the analysis techniques. However, comparisons 

with ambient data indicate that the emissions inventory for Sundays may not be representative of 

actual activity patterns on that day of the week, perhaps due to decreases in on-road mobile 

source emissions from Saturdays to Sundays, as well as inaccurate temporal characterizations of 

other source categories. Also, sources of VOC emissions appear to be missing or 

underrepresented in the emissions inventory near sites that are influenced by industrial and 

residential emissions, such as the Gary and Detroit-East 7 Mile sites. These results are consistent 

with previous top-down emissions evaluations for other regions, which show closest agreement 

between ambient- and emissions inventory-derived pollutant ratios on weekdays and at sites 

heavily impacted by on-road mobile source emissions (Chinkin and Reid, 2006). 

The on-road mobile source component of LADCO’s 2008 emissions inventory was 

developed using EPA’s MOVES model with default input data, and county-level outputs from 

MOVES were spatially allocated using spatial surrogate data.34 For the 2008 emissions 

inventory, agreement between ambient- and emissions-inventory derived pollutant ratios was 

generally poorer than was observed for the 2005 inventory. The greater discrepancy between 

ambient- and emissions inventory-derived pollutant ratios from 2005 to 2008 primarily results 

from large decreases in on-road NOx emissions that outpaced reductions in ambient NOx

concentrations. However, the Saturday-to-Sunday differences in pollutant ratio comparisons 

observed for the 2005 inventory were not observed for the 2008 inventory, as there was no 

variation between Saturday and Sunday on-road mobile source emissions in the 2008 inventory 

(as was the case for 2005). 

For both 2005 and 2008, the speciation of the VOC emissions inventory at all sites does 

not compare well with the hydrocarbon composition of the ambient data, resulting in a VOC 

emissions inventory that shows significantly more reactivity at all sites than the corresponding 

ambient data. As a result, ozone modeling efforts for the region may be influenced by 

“compensating errors,” as the underestimated magnitude of VOC emissions is offset by the 

overestimated reactivity of those emissions. The following key findings support these 

conclusions. 

 

34 LADCO plans to update the 2008 inventory with state-specific MOVES inputs and link-level activity data. The 

2008 inventory used in this analysis was the most current version as of April 29, 2011. 
Upper Midwest Emissions Inventory Evaluation Findings and Recommendations 

5-2

TNMOC/NOx Ratios 

For both 2005 and 2008, the agreement between overall ambient- and emissions 

inventory-derived TNMOC/NOx ratios is good (±20%) for the Jardine (2005 only) and 

Northbrook sites in Chicago. However, agreement is mediocre for the Milwaukee site, where the 

ambient-derived ratio is higher than the emissions-derived ratio by a factor of 1.8 in 2005 and a 

factor of 2.4 in 2008. Agreement is poor at the Detroit-East 7 Mile and Gary sites for 2005, 

where ambient-derived ratios were higher than emissions inventory-derived ratios by factors of 

2.7 and 3.6, respectively. 

 For 2005, ambient TNMOC concentrations are highest at the Gary and Detroit-East 7 

Mile sites. However, VOC emissions are lowest around the Gary site and are 18% lower 

at the East 7 Mile site than at the Jardine site (which has the lowest ambient TNMOC 

concentrations among all sites). These results suggest that some VOC sources are 

missing or underrepresented at Gary and East 7 Mile. At the Gary site, which is in a 

heavily industrialized area, point source TNMOC emissions may be underestimated. At 

the East 7 Mile site, which is in a suburban area, both residential sources of TNMOC and 

industrial sources, which impact the site when winds are from the southwest, may be 

underestimated. 

 For 2005, the agreement between ambient- and emissions inventory-derived 

TNMOC/NOx ratios is generally better on weekdays and Saturdays than on Sundays. 

The increased discrepancy between ambient- and emissions inventory-derived ratios on 

Sundays largely occurs because ambient TNMOC concentrations are similar on 

Saturdays and Sundays at most sites, while VOC emissions are consistently lower on 

Sundays than Saturdays. 

 At the Chicago-Northbrook and Milwaukee sites, overall TNMOC/NOx ratios derived 

from 2008 ambient data are higher than ratios derived from 2004–2006 data by 18% and 

46%, respectively. The higher 2008 ratios reflect increasing TNMOC concentrations and 

decreasing NOx concentrations at these sites. 

 For 2008, the overall emissions inventory-derived TNMOC/NOx ratio for ChicagoNorthbrook increased by 61% relative to 2005 and showed somewhat closer agreement to 

the ambient-derived ratio than in 2005. However, the overall emissions inventoryderived TNMOC/NOx ratio for the Milwaukee site was virtually unchanged from 2005 to 

2008, resulting in poorer agreement with the ambient-derived ratio in 2008 than in 2005. 

CO/NOx Ratios 

For 2005, the agreement between overall ambient- and emissions inventory-derived 

CO/NOx ratios is good (±30%) across all sites. However, at the Franklin and Mannheim sites in 

Chicago, the agreement between ambient- and emissions inventory-derived CO/NOx ratios is 

better on weekdays and Saturdays than on Sundays, as the emissions data do not completely 

account for the magnitude of the decrease in NOx concentrations from Saturdays to Sundays at 

those sites. 

For 2008, the agreement between overall ambient- and emissions inventory-derived 

CO/NOx ratios is mediocre (±30%) across all sites. At the Mannheim and Franklin sites in 
Upper Midwest Emissions Inventory Evaluation Findings and Recommendations 

5-3

Chicago, ambient-derived CO/NOx ratios were 5% to 39% lower than for 2005; however, 

emissions inventory-derived CO/NOx ratios increased by up to 35% at those sites. As a result, 

the ambient- and emissions-inventory derived ratios show poorer agreement for 2008 than for 

2005. The large increases in emissions inventory-derived CO/NOx ratios at these sites resulted 

from sharp decreases in on-road NOx emissions between 2005 and 2008. 

Speciation and Reactivity 

 The speciation of the emissions inventory tends to overestimate the contribution of 

acetylene, ethylene, toluene, and isoprene compared to the ambient data. Isoprene is 

highly reactive and short-lived in the atmosphere, and it therefore may be 

under-represented in the ambient data. The non-road mobile sector of the emissions 

inventory is the dominant source of acetylene, ethylene, and toluene emissions. 

 The speciation of the emissions inventory underestimates the contribution of ethane, 

propane, and C6-C11 alkanes at all sites and butane at the Chicago sites. However, 

ethane and propane are long-lived in the atmosphere and tend to accumulate; therefore, it 

is likely that the ambient monitors detected aged ethane and propane emissions. 

 Across all sites, the overall weighted reactivity value of the emissions inventory for the 

summer season is 16% to 80% higher than the weighted reactivity value of the ambient 

data. 

Based on the findings from this study, we recommend that the following steps be taken to 

further investigate the LADCO 2005 and 2008 emissions inventories and to make specific 

improvements to those inventories: 

 Improve the accuracy of weekend emissions estimates by collecting and analyzing 

day-specific on-road, non-road, and area source activity data to better characterize 

differences in weekday, Saturday, and Sunday activity levels. 

 Collect bottom-up emissions activity data for residential and industrial sources around 

the Gary, Detroit-East 7 Mile, and Milwaukee sites to “ground truth” the current 

VOC emissions inventories for these locations. 

 Employ source apportionment techniques, such as positive matrix factorization 

(PMF), to further evaluate the inventory around the Gary, Detroit-East 7 Mile, and 

Milwaukee sites and to identify specific source types that may be underestimated in 

the VOC inventories. 

 Evaluate the source(s) of large decreases in on-road NOx emissions in the 2008 

MOVES-based inventory relative to the 2005 MOBILE6.2-based inventory. 

 Review the speciation profiles assigned to on-road mobile sources and key off-road 

sources, such as lawn and garden equipment and aircraft. 

 Redo the 2008 pollutant ratio comparisons with additional ambient data (e.g., 

TNMOC measurements from the Jardine and Gary sites) and revised on-road mobile 

source inventories (i.e., on-road emissions developed using link-level activity data 

and state-specific MOVES inputs). 

Upper Midwest Emissions Inventory Evaluation References 

6-1

6. References 

Battye W. and Harris J. (2005) Improving modeling inventory data: speciation profiles. Draft 

technical report prepared for the Lake Michigan Air Directors Consortium, Des Plaines, 

IL, by EC/R Incorporated, Chapel Hill, NC, February. 

Brown S.G. (2006) Accountability–Tracking and evaluating air quality programs, Task 3–

Detroit, Michigan. Technical memorandum prepared for the U.S. Environmental 

Protection Agency, Research Triangle Park, NC, by Sonoma Technology, Inc., Petaluma, 

CA, STI-905213.05-3040-TM, September. 

California Air Resources Board (1997) Public meeting to consider approval and verification of 

the California emissions inventory. Report prepared by the Technical Support Division, 

Mobile Source Control Division, Office of Air Quality and Transportation Planning, 

California Environmental Protection Agency, Air Resources Board, Sacramento, CA, 

November. 

Carter W.P.L. (2003) The SAPRC-99 chemical mechanism and updated reactivity scales. 

Revised final report prepared for the California Air Resources Board, Sacramento, CA, 

by University of California, Center for Environmental Research and Technology, Air 

Pollution Research Center and College of Engineering, Riverside, CA, Contracts No. 92-

329 and 95-308, February. 

Chinkin L.R., Main H.H., and Roberts P.T. (2002) Weekday/weekend ozone observations in the 

South Coast Air Basin volume III: analysis of summer 2000 field measurements and 

supporting data. Final report prepared for National Renewable Energy Laboratory, 

Golden, CO, by Sonoma Technology, Inc., Petaluma, CA, STI-999670-2124-FR, April. 

Chinkin L.R., Penfold B.M., Brown S.G., and Hafner H.R. (2005) Emissions inventory 

evaluation and reconciliation in the South Coast Air Basin. Final report prepared for 

South Coast Air Quality Management District, Diamond Bar, CA, by Sonoma 

Technology, Inc., Petaluma, CA, STI-904045-2728-FR, August. 

Chinkin L.R. and Reid S.B. (2006) Emissions reconciliation findings and recommendations – 

Comparison of ambient measurements to emissions representations for modeling. 

Technical memorandum prepared for the California Air Resources Board, Sacramento, 

CA, by Sonoma Technology, Inc., Petaluma, CA, STI-905044.12-3094-TM, December. 

Desert Research Institute (2005) Validation of the U.S. EPA MOBILE6 highway vehicle 

emission factor model, Task 4: Guidance document for validation of on-road vehicle 

emissions inventory. Prepared for the Lake Michigan Air Directors Consortium 

(LADCO), Des Plaines, IL, by Desert Research Institute, Reno, NV, April. 

Fujita E.M., Croes B.E., Bennett C.L., Lawson D.R., Lurmann F.W., and Main H.H. (1992) 

Comparison of emissions inventory and ambient concentration ratios of CO, NMOG, and 

NOx in California’s South Coast Air Basin. J. Air Waste Manage. Assoc. 42, 264-276. 

LADCO (1998) Comparison of ambient and emissions VOC and NOx data in the Lake Michigan 

region. November. 

Pollack A.K., Lindhjem C., Stoeckenius T.E., Tran C., Mansell G., Jimenez M., Wilson G., and 

Coulter-Burke S. (2004) Evaluation of the U.S. EPA MOBILE6 highway vehicle 
Upper Midwest Emissions Inventory Evaluation References 

6-2

emission factor model. Final report prepared for the Coordinating Research Council 

(CRC), Alpharetta, GA, Emissions Inventory Improvement Program (EIIP), Research 

Triangle Park, NC, and U.S. EPA Office of Transportation and Air Quality (OTAQ), Ann 

Arbor, MI by ENVIRON International Corporation, Novato, CA, CRC Project E-64, 

March. 

Roberts P.T., Brown S.G., Reid S.B., Buhr M.P., Funk T.H., Stiefer P.S., Hopke P.K., and Kim 

E. (2004) Emissions inventory evaluation and reconciliation in the Houston-Galveston 

area. Final report prepared for the Houston Advanced Research Center, Texas 

Environmental Research Consortium, The Woodlands, TX, by Sonoma Technology, Inc., 

Petaluma, CA, STI-903640-2490-FR2, June. 

U.S. Environmental Protection Agency (2008) SPECIATE database, version 4.2. Available on 

the Internet at http://www.epa.gov/ttnchie1/software/speciate/index.html. November. 

U.S. Environmental Protection Agency (2010) Technical guidance on the use of MOVES2010 

for emissions inventory preparation in state implementation plans and transportation 

conformity. Prepared by the EPA's Office of Transportation and Air Quality, Ann Arbor, 

MI, EPA-420-B-10-023, April. Available on the Internet at 

http://www.epa.gov/otaq/models/moves/420b10023.pdf. 
Upper Midwest Emissions Inventory Evaluation Appendix A 

A-1

APPENDIX A 

Chemical Species Cross-Reference List 

Upper Midwest Emissions Inventory Evaluation Appendix A 

A-3

Table A-1. List of PAMS species used to match emissions and ambient data. 

Page 1 of 2

SAROAD 

Code CAS Code Species Name Molecular Weight 

MIR 

Value 

43203 74-85-1 Ethylene 28.054 9.07 

45201 71-43-2 Benzene 78.114 0.81 

43229 107-83-5 2-Methylpentane 86.178 1.78 

43230 96-14-0 3-Methylpentane 86.178 2.06 

43248 110-82-7 Cyclohexane 84.162 1.44 

43261 108-87-2 Methylcyclohexane 98.189 1.97 

43262 96-37-7 Methylcyclopentane 84.162 2.4 

43271 108-08-7 2,4-Dimethylpentane 100.205 1.63 

43274 565-59-3 2,3-Dimethylpentane 100.205 1.53 

43275 591-76-4 2-Methylhexane 100.205 1.36 

43276 540-84-1 2,2,4-Trimethylpentane 114.232 1.43 

43279 565-75-3 2,3,4-Trimethylpentane 114.232 1.22 

43291 75-83-2 2,2-Dimethylbutane 86.178 1.33 

43295 589-34-4 3-Methylhexane 100.205 1.84 

43298 589-81-1 3-Methylheptane 114.232 1.33 

98001 79-29-8 2,3-Dimethylbutane 86.178 1.13 

98140 592-27-8 2-Methylheptane 114.232 1.18 

43213 106-98-9 1-Butene 56.108 10.22 

43216 624-64-6 Trans-2-Butene 56.108 13.9 

43217 590-18-1 cis-2-Butene 56.108 13.22 

43224 109-67-1 1-Pentene 70.135 7.73 

43226 646-04-8 Trans-2-Pentene 70.135 10.23 

43227 627-20-3 cis-2-Pentene 70.135 10.23 

98005 592-76-7 1-Heptene 98.189 4.2 

45107 25551-13-7 Trimethylbenzene 120.195 9.9 

45113 141-93-5 1,3-Diethylbenzene 134.222 8.39 

45114 105-05-5 1,4-Diethylbenzene 134.222 3.36 

45203 100-41-4 Ethylbenzene 106.168 2.79 

45204 95-47-6 o-Xylene 106.168 7.48 

45207 108-67-8 1,3,5-Trimethylbenzene 120.195 11.22 

45208 95-63-6 1,2,4-Trimethylbenzene 120.195 7.18 

45209 103-65-1 N-Propylbenzene 120.195 2.2 

98043 98-82-8 Isopropylbenzene (Cumene) 120.195 2.32 

99914 622-96-8 1-Methyl-4-Ethylbenzene 120.195 3.75 

99915 611-14-3 1-Methyl-2-Ethylbenzene 120.195 6.61 

43551 67-64-1 Acetone 58.0804 0.43 
Upper Midwest Emissions Inventory Evaluation Appendix A 

A-4

Table A-1. List of PAMS species used to match emissions and ambient data. 

Page 2 of 2

SAROAD 

Code CAS Code Species Name Molecular Weight 

MIR 

Value 

45220 100-42-5 Styrene 104.152 1.94 

43502 50-00-0 Formaldehyde 30.0264 8.96 

43202 74-84-0 Ethane 30.07 0.31 

43204 74-98-6 Propane 44.097 0.56 

43212 106-97-8 n-Butane 58.124 1.32 

43214 75-28-5 Isobutane 58.124 1.34 

43220 109-66-0 n-Pentane 72.151 1.53 

43242 287-92-3 Cyclopentane 70.135 2.67 

98132 78-78-4 Isopentane 72.151 1.67 

43205 115-07-1 Propylene 42.081 11.57 

45202 108-88-3 Toluene 92.141 3.97 

43503 75-07-0 Acetaldehyde 44.0534 6.83 

43206 74-86-2 Acetylene 26.038 1.24 

43243 78-79-5 Isoprene 68.119 10.68 

43231 110-54-3 n-Hexane 86.178 1.43 

43233 111-65-9 n-Octane 114.232 1.09 

43235 111-84-2 n-Nonane 128.259 0.93 

43238 124-18-5 n-Decane 142.286 0.81 

43241 1120-21-4 n-Undecane 156.313 0.72 
Upper Midwest Emissions Inventory Evaluation Appendix B 

B-1

APPENDIX B 

Monitoring Site Photographs 

B-3 

Looking North Looking East Looking West Looking South Figure B-1. Photographs taken around the Chicago-Jardine monitoring site. 
B-4 

Looking North Looking East Looking West Looking South Figure B-2. Photographs taken around the Chicago-Northbrook monitoring site. 
B-5 

Looking North Looking East Looking West Looking South Figure B-3. Photographs taken around the Chicago-Mannheim monitoring site. 
B-6 

Looking North Looking East Looking West Looking South Figure B-4. Photographs taken around the Gary, Indiana, monitoring site. 
B-7 

Looking North Looking East Looking West Looking South Figure B-5. Photographs taken around the Milwaukee, Wisconsin, monitoring site. 
B-8 

Looking North Looking East Looking West Looking South Figure B-6. Photographs taken around the Detroit-East 7 Mile monitoring site. 
B-9 

Looking Northwest Looking Northeast Looking Southwest Looking Southeast Figure B-7. Photographs taken around the Detroit-Linwood monitoring site.
Upper Midwest Emissions Inventory Evaluation Appendix B 

B-10

Figure B-8. Photograph of the Chicago-Franklin monitoring site. 
Upper Midwest Emissions Inventory Evaluation Appendix B 

B-11

Figure B-9. Image of the area around the Jardine and Franklin sites in Chicago. 
Upper Midwest Emissions Inventory Evaluation Appendix B 

B-12

Figure B-10. Image of the area around the Northbrook site in Chicago. 
Upper Midwest Emissions Inventory Evaluation Appendix B 

B-13

Figure B-11. Image of the area around the Mannheim site in Chicago. 
Upper Midwest Emissions Inventory Evaluation Appendix B 

B-14

Figure B-12. Image of the area around the Gary site. 
Upper Midwest Emissions Inventory Evaluation Appendix B 

B-15

Figure B-13. Image of the area around the East 7 Mile and Linwood sites in Detroit. 
Upper Midwest Emissions Inventory Evaluation Appendix B 

B-16

Figure B-14. Image of the area around the Milwaukee site. 
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-1

APPENDIX C 

Diurnal Concentration Plots for 2008 and 2009 

Upper Midwest Emissions Inventory Evaluation Appendix C 

C-3

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Figure C-1. Hourly TNMOC and NOx concentrations for the Chicago-Northbrook site for 

summer weekdays (left), Saturdays (center), and Sundays (right), 2008. 
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-4

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Figure C-2. Hourly TNMOC and NOx concentrations for the Chicago-Northbrook site for 

summer weekdays (left), Saturdays (center), and Sundays (right), 2009.
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-5

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Figure C-3. Hourly TNMOC and NOx concentrations for the Milwaukee site for summer 

weekdays (left), Saturdays (center), and Sundays (right), 2008. 
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-6

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Figure C-4. Hourly CO and NOx concentrations for the Chicago-Franklin site for summer 

weekdays (left), Saturdays (center), and Sundays (right), 2008. 
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-7

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Figure C-5. Hourly CO and NOx concentrations for the Chicago-Franklin site for summer 

weekdays (left), Saturdays (center), and Sundays (right), 2009.
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-8

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Figure C-6. Hourly CO and NOx concentrations for the Chicago-Mannheim site for 

summer weekdays (left), Saturdays (center), and Sundays (right), 2008. 
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-9

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Figure C-7. Hourly CO and NOx concentrations for the Chicago-Mannheim site for 

summer weekdays (left), Saturdays (center), and Sundays (right), 2009. 
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-10

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Figure C-8. Hourly CO and NOx concentrations for the Chicago-Northbrook site for 

summer weekdays (left), Saturdays (center), and Sundays (right), 2008. 
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-11

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Figure C-9. Hourly CO and NOx concentrations for the Chicago-Northbrook site for 

summer weekdays (left), Saturdays (center), and Sundays (right), 2009.
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-12

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Figure C-10. Hourly CO and NOx concentrations for the Chicago-Mannheim site for 

winter weekdays (left), Saturdays (center), and Sundays (right), 2008. 
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-13

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Figure C-11. Hourly CO and NOx concentrations for the Chicago-Mannheim site for 

winter weekdays (left), Saturdays (center), and Sundays (right), 2009.
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-14

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Figure C-12. Hourly CO and NOx concentrations for the Chicago-Franklin site for winter 

weekdays (left), Saturdays (center), and Sundays (right), 2008. 
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-15

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Figure C-13. Hourly CO and NOx concentrations for the Chicago-Franklin site for winter 

weekdays (left), Saturdays (center), and Sundays (right), 2009.
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-16

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Figure C-14. Hourly CO and NOx concentrations for the Chicago-Northbrook site for 

winter weekdays (left), Saturdays (center), and Sundays (right), 2008. 
Upper Midwest Emissions Inventory Evaluation Appendix C 

C-17

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500

CO (ppb)

0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223

Hour

0

100

200

300

400

500

CO (ppb)

0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223

Hour

0

100

200

300

400

500

CO (ppb)

0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223

Hour

0

20

40

60

80

NOx (ppb)

0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223

Hour

0

20

40

60

80

NOx (ppb)

0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223

Hour

0

20

40

60

80

NOx (ppb)

Figure C-15. Hourly CO and NOx concentrations for the Chicago-Northbrook site for 

winter weekdays (left), Saturdays (center), and Sundays (right), 2009.

Upper Midwest Emissions Inventory Evaluation Appendix D 

D-1

APPENDIX D 

Additional Comparisons of Pollutant Ratios 

Upper Midwest Emissions Inventory Evaluation Appendix D 

 D-3

0

2

4

6

678678678678678

E7Mile Gary Jardine Northbrook Milw aukee

Ambient Ratio Median/Emission Ratio

All

WD

SAT

SUN

Figure D-1. Ratios of ambient-derived TNMOC/NOx ratios to emissions-derived TNMOC/NOx

ratios by month and day of week for 20051

 (the 1:1 agreement line is shown as a dashed red 

line). 

 

1

 Because the 2005 emissions inventory was compared to ambient data from a three-year period (2004-2006), the 

large number of ambient samples allowed for month-specific (and other) analyses that were not possible with the 

2008 ambient-to-emissions comparisons. 
Upper Midwest Emissions Inventory Evaluation Appendix D 

 D-4

0

1

2

3

4

1234

Wind Quadrant

TNMOC/NOx Ratio

0

1

2

3

4

1234

Wind Quadrant

0

1

2

3

4

1234

Wind Quadrant

Ambient

EI - Low Level Only

EI - With Elevated

Source

Figure D-2. Summer 2005 TNMOC/NOx ratios by wind quadrant for the Chicago-Jardine site on 

weekdays (left), Saturdays (center), and Sundays (right). 

0

1

2

3

4

5

6

7

1234

Wind Quadrant

TNMOC/NOx Ratio

0

1

2

3

4

5

6

7

1234

Wind Quadrant

0

1

2

3

4

5

6

7

1234

Wind Quadrant

Ambient

EI - Low Level Only

EI - With Elevated

Source

Figure D-3. Summer 2005 TNMOC/NOx ratios by wind quadrant for the Chicago-Northbrook site 

on weekdays (left), Saturdays (center), and Sundays (right). 

0

5

10

15

1234

Wind Quadrant

TNMOC/NOx Ratio

0

5

10

15

1234

Wind Quadrant

0

5

10

15

1234

Wind Quadrant

Ambient

EI - Low Level Only

EI - With Elevated

Source

Figure D-4. Summer 2005 TNMOC/NOx ratios by wind quadrant for the Gary site on weekdays 

(left), Saturdays (center), and Sundays (right). 
Upper Midwest Emissions Inventory Evaluation Appendix D 

 D-5

0

5

10

15

20

1234

Wind Quadrant

TNMOC/NOx Ratio

0

5

10

15

20

1234

Wind Quadrant

0

5

10

15

20

1234

Wind Quadrant

Ambient

EI - Low Level Only

EI - With Elevated

Source

Figure D-5. Summer 2005 TNMOC/NOx ratios by wind quadrant for the Detroit – East 7 Mile site 

on weekdays (left), Saturdays (center), and Sundays (right). 

0

1

2

3

4

5

6

7

8

9

1234

Wind Quadrant

TNMOC/NOx Ratio

0

1

2

3

4

5

6

7

8

9

1234

Wind Quadrant

0

1

2

3

4

5

6

7

8

9

1234

Wind Quadrant

Ambient

EI - Low Level Only

EI - With Elevated

Source

Figure D-6. Summer 2005 TNMOC/NOx ratios by wind quadrant for the Milwaukee site on 

weekdays (left), Saturdays (center), and Sundays (right). 

0

1

2

3

12 1 2 6 7 8 12 1 2 6 7 8 12 1 2 6 7 8 12 1 2 6 7 8

Franklin Linw ood Mannheim Milw aukee

Ambient Ratio Median/Emission Ratio

All

WD

SAT

SUN

Figure D-7. Ratios of ambient-derived CO/NOx ratios to emissions-derived CO/NOx ratios by 

month and day of week for 2005 (the 1:1 agreement line is shown as a dashed red line). 
Upper Midwest Emissions Inventory Evaluation Appendix D 

 D-6

0

5

10

15

20

25

1234

Wind Quadrant

CO/NOx Ratio 

0

5

10

15

20

25

1234

Wind Quadrant

0

5

10

15

20

25

1234

Wind Quadrant

Ambient

EI - Low Level Only

EI - With Elevated

Source

Figure D-8. Winter 2005 CO/NOx ratios by wind quadrant for the Chicago-Mannheim site on 

weekdays (left), Saturdays (center), and Sundays (right). 

0

5

10

15

20

25

1234

Wind Quadrant

CO/NOx Ratio 

0

5

10

15

20

25

1234

Wind Quadrant

0

5

10

15

20

25

1234

Wind Quadrant

Ambient

EI - Low Level Only

EI - With Elevated

Source

Figure D-9. Summer 2005 CO/NOx ratios by wind quadrant for the Chicago-Mannheim site on 

weekdays (left), Saturdays (center), and Sundays (right). 

0

5

10

15

20

25

1234

Wind Quadrant

CO/NOx Ratio 

0

5

10

15

20

25

1234

Wind Quadrant

0

5

10

15

20

25

1234

Wind Quadrant

Ambient

EI - Low Level Only

EI - With Elevated

Source

Figure D-10. Winter 2005 CO/NOx ratios by wind quadrant for the Milwaukee site on weekdays 

(left), Saturdays (center), and Sundays (right). 
Upper Midwest Emissions Inventory Evaluation Appendix D 

 D-7

0

5

10

15

20

25

1234

Wind Quadrant

CO/NOx Ratio 

0

5

10

15

20

25

1234

Wind Quadrant

0

5

10

15

20

25

1234

Wind Quadrant

Ambient

EI - Low Level Only

EI - With Elevated

Source

Figure D-11. Summer 2005 CO/NOx ratios by wind quadrant for the Milwaukee site on weekdays 

(left), Saturdays (center), and Sundays (right). 

Upper Midwest Emissions Inventory Evaluation Appendix E 

E-1

APPENDIX E 

Additional Comparisons of 

Hydrocarbon Compositions 

Upper Midwest Emissions Inventory Evaluation Appendix E 

E-3

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-1. Comparison of 2005 summer weekday ambient- and emissions-derived 

hydrocarbon compositions for the Chicago-Jardine site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-2. Comparison of 2005 summer Saturday ambient- and emissions-derived 

hydrocarbon compositions for the Chicago-Jardine site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-4

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-3. Comparison of 2005 summer Sunday ambient- and emissions-derived 

hydrocarbon compositions for the Chicago-Jardine site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-4. Comparison of June 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Chicago-Jardine site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-5

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-5. Comparison of July 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Chicago-Jardine site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-6. Comparison of August 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Chicago-Jardine site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-6

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-7. Comparison of 2005 summer weekday ambient- and emissions-derived 

hydrocarbon compositions for the Chicago-Northbrook site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-8. Comparison of 2005 summer Saturday ambient- and emissions-derived 

hydrocarbon compositions for the Chicago-Northbrook site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-7

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-9. Comparison of 2005 summer Sunday ambient- and emissions-derived 

hydrocarbon compositions for the Chicago-Northbrook site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-10. Comparison of June 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Chicago-Northbrook site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-8

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-11. Comparison of July 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Chicago-Northbrook site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-12. Comparison of August 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Chicago-Northbrook site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-9

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-13. Comparison of 2005 summer weekday ambient- and emissions-derived 

hydrocarbon compositions for the Detroit-East 7 Mile site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-14. Comparison of 2005 summer Saturday ambient- and emissions-derived 

hydrocarbon compositions for the Detroit-East 7 Mile site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-10

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-15. Comparison of 2005 summer Sunday ambient- and emissions-derived 

hydrocarbon compositions for the Detroit-East 7 Mile site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-16. Comparison of June 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Detroit-East 7 Mile site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-11

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-17. Comparison of July 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Detroit-East 7 Mile site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-18. Comparison of August 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Detroit-East 7 Mile site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-12

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-19. Comparison of 2005 summer weekday ambient- and emissions-derived 

hydrocarbon compositions for the Milwaukee site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-20. Comparison of 2005 summer Saturday ambient- and emissions-derived 

hydrocarbon compositions for the Milwaukee site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-13

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-21. Comparison of 2005 summer Sunday ambient- and emissions-derived 

hydrocarbon compositions for the Milwaukee site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-22. Comparison of June 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Milwaukee site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-14

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-23. Comparison of July 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Milwaukee site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-24. Comparison of August 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Milwaukee site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-15

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-25. Comparison of 2005 summer weekday ambient- and emissions-derived 

hydrocarbon compositions for the Gary site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-26. Comparison of 2005 summer Saturday ambient- and emissions-derived 

hydrocarbon compositions for the Milwaukee site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-16

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-27. Comparison of 2005 summer Sunday ambient- and emissions-derived 

hydrocarbon compositions for the Milwaukee site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-28. Comparison of June 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Milwaukee site. 
Upper Midwest Emissions Inventory Evaluation Appendix E 

E-17

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-29. Comparison of July 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Milwaukee site. 

0%

5%

10%

15%

20%

25%

30%

EthyleneBenzene

C6+ AlkanesC4+ Alkenes

C8+ Aromatics

Styrenes

Ethane

PropaneButanes

Pentanes

Propylene

Toluene

Acetylene

Isoprene

C6-C11 Alkanes

% TNMOC

Ambient

Emissions

Figure E-30. Comparison of August 2005 ambient- and emissions-derived hydrocarbon 

compositions for the Milwaukee site.