Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Pollutant | Type | Standard | Averaging Time | Regulatory Citation |
| --- | --- | --- | --- | --- |
| SO 2 | Primary | 0.14 ppm (365 μg / m 3 ) | 24-hour | 40 CFR 50.4(b) |
| SO 2 | Primary | 0.030 ppm (80 μg/m³) | annual | 40 CFR 50.4(a) |
| SO 2 | Secondary | 0.5 ppm (1,300 μg/m³) | 3-hour | 40 CFR 50.5(a) |
| PM 10 | Primary and Secondary | 150 μg/m³ | 24-hour | 40 CFR 50.6(a) |
| PM 2.5 | Secondary | 35 μg/m³ | 24-hour | 40 CFR 50.7(a) |
| PM 2.5 | Primary | 15 μg/m³ | annual | 40 CFR 50.7(a) |
| CO | Primary | 35 ppm (40 mg /m³) | 1-hour | 40 CFR 50.8(a)(2) |
| CO | Primary | 9 ppm (10mg/m³) | 8-hour | 40 CFR 50.8(a)(1) |
| O 3 | Primary and Secondary | 0.12 ppm (235 μg/m³) | 1-hour | 40 CFR 50.9(a) |
| O 3 | Primary and Secondary | 0.075 ppm (150 μg/m³) | 8-hour | 40 CFR 50.10(a) |
| NO 2 | Primary and Secondary | 0.053 ppm (100 μg/m³) | annual | 40 CFR 50.11(a) and (b) |
| Pb | Primary and Secondary | 0.15 μg/m³ | Rolling 3 months | 40 CFR 50.12 |
Question:
what is the regulatory citation when the standard is 15 μg/m³?
Answer:
40 CFR 50.7(a)