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Air Quality 101

April, 2016: Comparing Air Quality Between States

Many people like to compare air quality between different areas of the country to determine who has the cleanest air . The U.S. Environmental Protection Agency recently added an interactive tool called AirCompare to its website to do just that. I tried using it to compare ozone levels between Indianapolis and New York City . Indianapolis was shown as having much worse air quality. This was puzzling. When I investigated closer, what was actually being compared was air quality in Marion County, Indiana versus Kings County, New York. Marion County, Indiana had a population of 934,243 in 2014 and had 5 ozone monitors. Kings County, New York had a population of 2,621,793 in 2014 and no ozone monitors. This caused me to wonder how many other similar counties had no ozone monitors, which led to the following analysis.

For each county or equivalent I determined the 2014 population and the land area in square miles. I also determined the 2011 emission rate of volatile organic compounds (VOC) and nitrogen oxides (NOx) from U.S. EPA’s National Emissions Inventory . Data for 2011 is the most recent data available. These two pollutants combine to form ozone. With this data I calculated the highest ten counties that did not have ozone monitors in 2014 based upon: population, population density, VOC emissions, VOC density, NOx emissions and NOx density. I set one further criteria. The area of the county, or equivalent, must be at least 50 square miles to remove small cities that have very small land areas that lead to large densities. Table 1 shows the counties based upon the 2014 population. Kings County, NY tops the list. The overall rank shows the rank among all counties including those that monitor ozone.

Table 1: Top Ten Counties without Ozone Monitors Based on Population
Rank County/State 2014 Population Overall Rank
1 Kings County, NY 2,621,793 8
2 Nassau County, NY 1,358,627 28
3 Snohomish County, WA 759,583 81
4 Fort Bend County, TX 685,345 91
5 Jackson County, MO 683,191 92
6 Union County, NJ 552,939 118
7 Ramsey County, MN 532,655 124
8 Williamson County, TX 489,250 139
9 Virginia Beach city, VA 450,980 150
10 Burlington County, NJ 449,722 151

While it is understood that U.S. EPA’s monitoring strategy does not require every single county in a Metropolitan Statistical Area to have an ozone monitor, shouldn’t the most populated counties in the nation have ozone monitors?

However, all counties are not the same size. So perhaps the better comparison is on population density (population divided by the land area in square miles). Table 2 shows this data. Kings County, NY is still number one.

Table 2: Top Ten Counties without Ozone Monitors Based on Population Density
Rank County/State Population Density Overall Rank
1 Kings County, NY 36,927 2
2 Union County, NJ 5,368 18
3 Nassau County, NY 4,734 20
4 Norfolk city, VA 4,545 22
5 Richmond city, VA 3,631 30
6 Ramsey County, MN 3,414 31
7 Newport News city, VA 2,691 45
8 Clayton County, GA 1,871 73
9 Virginia Beach city, VA 1,818 76
10 Howard County, MD 1,227 121

Perhaps population is not the only parameter that should be used for monitor selection. Table 3 looks at VOC emissions by county to determine the counties with the highest VOC emissions that do not have ozone monitors.

Table 3: Top Ten Counties without Ozone Monitors Based on VOC Emissions
Rank County/State Emissions (Tons Per Year [TPY]) Overall Rank
1 Southeast Fairbanks Borough, AK 194,258 1
2 Yukon-Koyukuk Borough, AK 186,548 2
3 Cameron Parish, LA 133,186 4
4 North Slope Borough, AK 126,177 5
5 Greenlee County, AZ 124,326 6
6 Apache County, AZ 105,123 11
7 Washington County, NY 67,191 21
8 Mountrail County, ND 57,572 26
9 Lemhi County, ID 54,766 27
10 Idaho County, ID 48,361 28

Five of the six counties with the highest VOC emissions do not have ozone monitors. While some may argue that three are in Alaska, are we sure that given these levels of emissions and sunlight for 24 hours a day, that the new ozone standard would be met if monitors were there?

Perhaps we should be looking at VOC emission density since many of the counties included in Table 3 are large in size. Table 4 looks at this data.

Table 4: Top Ten Counties without Ozone Monitors Based on VOC Emissions Density
Rank County/State VOC Emissions Density (TPY/sq mi) Overall Rank
1 Kings County, NY 346.9 2
2 Union County, NJ 106.1 25
3 Norfolk County, VA 104.6 26
4 Ramsey County, MN 101.5 28
5 Cameron Parish, LA 101.4 29
6 Richmond city, VA 90.6 31
7 Nassau County, NY 86.4 34
8 Washington County, NY 80.5 36
9 Greenlee County, AZ 67.3 47
10 Newport News city, VA 66.2 50

The list shifts significantly when switching to VOC density instead of VOC emissions. Kings County, NY pops up on top again.

The other pollutant that leads to ozone formation is nitrogen oxides (NOx). Table 5 shows the top ten counties with the most NOx emissions that do not have ozone monitors.

Table 5: Top Ten Counties without Ozone Monitors Based on NOx Emissions
Rank County/State 2011 NOx Emissions (TPY) Overall Rank
1 North Slope Borough, AK 49,821 10
2 Plaquemine Parish, LA 37,944 24
3 York County, PA 33,393 42
4 Emmons County, ND 31,711 45
5 Millard County, UT 31,284 48
6 Jackson County, MO 28,255 59
7 Apache County, AZ 28,021 62
8 Miller County, GA 27,039 64
9 Monroe County, MI 25,682 68
10 Rogers County, OK 24,541 71

Finally Table 6 shows the top ten counties that have the highest NOx emissions density but have no ozone monitors.

Table 6: Top Ten Counties without Ozone Monitors Based on NOx Emissions Density
Rank County/State NOx Emissions Density (TPY/sq mi) Overall Rank
1 Kings County, NY 267.6 5
2 Union County, NJ 132.2 15
3 Richmond city, VA 115.1 19
4 Montour County, PA 105.7 23
5 Norfolk city, VA 105.3 24
6 Ramsey County, MN 105.1 25
7 Miller County, GA 95.5 29
8 Nassau County, NY 83.4 34
9 Carroll County, KY 74.7 39
10 Clayton County, GA 73.7 41

The point of these comparisons is that when comparing air quality between states, it is difficult to assess whether both states are adequately measuring ozone levels. If counties with large populations, large population densities, or large VOC or NOx emissions are not being monitored, comparisons may be less than accurate.

Comments on this article and/or any previous article can be sent to kbaugues@idem.in.gov.

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