Motor vehicles moving through completed areas of the Big Dig have not released an excess of dangerous emissions into the atmosphere, but the situation will continue to be monitored, officials said yesterday during a presentation on the Central Artery/Tunnel Project Operation and Air Quality.

The Massachusetts Department of Environmental Protection (DEP) and special teams formed to oversee the emissions standards of the project have been monitoring the project since before its beginning in 1991.

Emissions standards, called National Ambient Air Quality Standards, must comply with those standards mandated by the Federal Highway Administration and the Environmental Protection Agency. With the northbound lanes of Interstate 93 set to open tomorrow, officials said so far the project has had very little effect on air quality in areas where traffic is already flowing.

‘The levels that we’ve seen for I-90 have been extremely low,’ said Alex Kasprak, lead air quality engineer for the project. However, Kasprak said traffic levels are currently at about 35,000 to 45,000 cars per day, less than the ultimate expected traffic limit of 90,000 cars per day.

Before the project began, computer technology was used to estimate the reality of air quality, said Robert Tuchmann, chair of the Central Artery Environmental Oversight Committee. He said data is monitored both in the tunnel for drivers and in the vent stacks where the air is released into the atmosphere, which could affect residents living near the stacks.

‘The goal is to protect all of us in cars and on the street,’ Tuchmann said.

But Tuchmann said a committee is limited in its control of air standards. He added that federal regulations for car exhaust systems should be improved to help overall air quality, a topic he said has not been discussed much in Congress.

The study tests for pollutants such as carbon monoxide, an asphyxiate; nitrous oxide, which poses a threat to the ozone layer; non-methane hydrocarbons and particulate matter that could cause respiratory problems, Kasprak said.

The project has posed some challenges for the engineers, most notably the lack of a set level of emissions for non-methane hydrocarbons (NMHC). The data collected for NMHC will be evaluated at the end of the project and compared to the data collected in 1991.

‘There’s been a lot of data collected, a lot of lessons learned,’ said Jerome Grafe, regional planner for Transportation Management Programs from the Massachusetts DEP. ‘It’s a unique project.’

Drivers can tolerate less carbon monoxide gas the longer they spend in a tunnel, Kasprak said. There are carbon monoxide detectors every 1,000 feet in the tunnel, and when a computer detects an excess of the gas, one of six ventilation towers included in the project is programmed to release more fresh air into the tunnel, he said. The air is circulated through jet fans and is released into the tunnels through slots originating underneath the roadway. The towers also release air from the tunnels back into the atmosphere.

DEP standards require data from the ventilation towers to be logged and recorded daily. The committee will offer monthly reports for the first year of the project and yearly reports thereafter, as per requirements. The data will then be reanalyzed every five years.

The committee is also required to identify ways to eliminate the occurrence of excess pollutants, show the impact of any possible excursions and provide mitigation plans to demonstrate how control measures will be implemented.

The project is expected to be completed in 2004. Emission data is expected to be ready 12 to 15 months after the opening.