Daily Air Quality Index summaries from EPA monitors in Union, South Carolina, 1983–2007.
54%
Good days in 2007
50
Median daily AQI, 2007
12
Days above 100 in 2007
237
Days with an AQI in 2007 (of 365)
In 2007, EPA reported a daily Air Quality Index (AQI) for Union, South Carolina on 237 days. 127 of those days (54%) were in the Good range, and the median daily AQI was 50. That median is higher than the typical monitored county in South Carolina (median 47 across 21 counties), and higher than the typical monitored U.S. county (46). The main pollutant was ozone on 237 days. Across the years with fuller monitoring, the share of Good days fell: an average of 70% in 1984–1986 versus 61% in 2005–2007.
EPA did not report an AQI for every day of 2007 here (237 of 365 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.
The most recent year with data for this county is 2007; EPA's files for 2008–2025 contain no row for it, which usually means its monitors stopped reporting.
Years with fewer than 120 monitored days (1983) are shown in the table but left out of comparisons and trend statements.
How the days broke down each year
Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.
Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous
Typical and high-end AQI over time
The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.
Median daily AQI
90th-percentile daily AQI
Main pollutant by day, 2007
On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.
Pollutant
Days as main pollutant
Share of monitored days
Ozone
237
100%
Year-by-year data
Annual AQI summary by year
Year
Days with AQI
Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous
Median AQI
90th pct.
Max AQI
Main pollutant
2007
237
127
98
12
0
0
0
50
87
129
Ozone
2006
221
130
81
10
0
0
0
46
87
136
Ozone
2005
219
152
55
12
0
0
0
43
87
150
Ozone
2004
237
162
70
5
0
0
0
43
84
115
Ozone
2003
229
174
43
12
0
0
0
41
87
147
Ozone
2002
219
127
59
30
3
0
0
47
115
177
Ozone
2001
296
202
68
26
0
0
0
43
97
143
Ozone
2000
353
243
92
17
1
0
0
41
90
154
Ozone
1999
360
253
79
25
2
1
0
41
97
203
Ozone
1998
350
244
71
30
5
0
0
41
101
174
Ozone
1997
357
258
77
22
0
0
0
39
84
150
Ozone
1996
359
290
58
10
1
0
0
37
71
151
Ozone
1995
330
264
60
5
1
0
0
33
67
164
Ozone
1994
292
224
58
8
2
0
0
38
74
172
Ozone
1993
301
201
78
19
3
0
0
44
90
161
Ozone
1992
298
245
44
9
0
0
0
36
67
143
Ozone
1991
355
276
75
4
0
0
0
38
71
126
Ozone
1990
312
213
76
21
2
0
0
43
90
190
Ozone
1989
261
202
49
10
0
0
0
35
80
140
Ozone
1988
263
199
44
17
3
0
0
38
97
164
Ozone
1987
349
210
87
44
7
1
0
44
119
203
Ozone
1986
325
204
85
32
4
0
0
41
108
174
Ozone
1985
311
236
62
12
1
0
0
37
80
151
Ozone
1984
300
212
62
23
3
0
0
42
97
159
Ozone
1983
86
72
9
5
0
0
0
37
87
133
Ozone
What this data can and can’t tell you
It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.
It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.
Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.
Counties in South Carolina with a similar median AQI in 2007
