Posts Tagged ‘sulfur dioxide’

Proposed Air Quality Standards for Sulfur Dioxide

Wednesday, December 9th, 2009

by Phil DeVita

For the first time since 1971, the Environmental Protection Agency (EPA) has proposed to revise the National Ambient Air Quality Standards for sulfur dioxide (SO2).  The proposal calls for a new 1-hour standard.  The current SO2 standard consists of a primary 24-hour and annual standard.  There is also a secondary 3-hour standard.  The primary standards were set to protect the public health including the health of the sensitive population (e.g. asthmatics, children, and the elderly).  The secondary standard was established to address public welfare and the environment.  Recent health studies have linked short-term (e.g. ranging from 5 minutes to 24-hours) SO2 exposures to adverse respiratory effects including increased asthma symptoms and bronchoconstriction.

The EPA is currently taking comments on the new 1-hour standard ranging from 50 and 100 parts per billion (ppb).  Since the revised standard would be more protective, the EPA is proposing to revoke the current 24-hour and annual standard.  The current proposal only addresses the primary standards.  EPA will address the secondary standard (e.g. 3-hour) under a second proposal in 2011.  The current and proposed SO2 standards are presented in the following tables.

Current Standards

Averaging Time

Primary Standards

Secondary Standards

3-Hour

none

500 ppb

24-Hour

140 ppb

none

Annual

30 ppb

none

Proposed Standards

Averaging Time

Primary Standards

Secondary Standards

1-Hour

(50 to 100 ppb)

none

3-Hour

none

500 ppb

24-Hour

Revoke

none

Annual

Revoke

None

EPA is also proposing changes to the monitoring requirements for SO2.  Monitors would be placed in urban areas and areas with high SO2 emission levels.  The proposal includes changing the Air Quality Index (AQI) to reflect the new standards thereby improving states’ abilities to alert the public when short-term levels may affect their health.

The public comment period is open for 60 days after the proposal is published in the Federal Register.  EPA will hold a public hearing on January 5, 2010 in Atlanta.   EPA must issue a final decision by June 2, 2010.

The proposed SO2 revision comes off the heels of EPA’s recent proposal to revise the nitrogen dioxide (NO2) standard.  EPA is proposing to include a new 1-hour NO2 standard ranging from 80-100 ppb while also soliciting comments as low as 65 ppb and  up to 150 ppb.  The proposal would retain the current annual standard of 53 ppb.  The comment period has closed on the NO2 standard and EPA must issue a final decision by January 22, 2010.

These proposed standards will affect all types of emission sources, including aviation.  For areas in non-attainment and maintenance regions, general conformity determinations will need to demonstrate that project emissions will not exceed these standards prior to FAA approving federal funding.