Carbon Emissions: Improving the Estimate in New York


New York City’s carbon emissions would have exceeded 50.7 million tons in 2017 according to some estimates. However, it is quite difficult to know if these data are really accurate, as they are collected on only a few pollution sources. Thus, if the calculations are incorrect or the process is flawed, the emissions inventory could be skewed.

Carbon emissions: the current situation in New York

On New York City’s carbon emissions, Roisin Commane, an atmospheric chemist at Columbia University’s Lamont-Doherty Earth Observatory, has developed a way to directly measure the city’s greenhouse gas (GHG) emissions.

The chemist’s process would like to put an instrument on a large building in Harlem to measure local air pollutant levels from top to bottom.

Currently, estimates of carbon dioxide, methane, and carbon monoxide emissions from New York City vary considerably depending on the method used for the calculations.

Roisin Commane explains that:

Some seem more realistic than others. But we don’t know what is correct without these “top-down” measurements in the atmosphere, and we won’t know what we are missing.

The Commane method

Start of measurements in 2019

As of January 2019, Commane and his team have begun measuring greenhouse gas emissions from the rooftop observatory at City College of New York.

The observatory is located close enough to the city center so that the measuring instrument can detect the different levels of pollution in the air.

Roisin Commane explained in an article of
Earth Institute Columbia University

“It’s unusual to have a site that can do that […] We can’t exactly put a tower in the middle of New York City, so that’s kind of the next best thing.”

Since then, the device has already begun to prove itself. In particular, it revealed temporary reductions in air pollution and global warming emissions while the city was dealing with Covid-19. For example, during the New York City shutdown in March, the instrument measured a 10% decrease in CO2 and methane levels and a 50% decrease in carbon monoxide concentration compared to the previous spring.

The ring cavity spectrometer

The device set up by Ms. Commane’s team is known as a ring cavity spectrometer. The latter works by bouncing an infrared laser several times through a tube filled with air drawn from the surrounding environment.

This machine allows the team to determine the concentration of greenhouse gases in the atmosphere.

So when the spectrometer measures a change in air concentrations, Dr. Luke Schiferl analyzes the results. In effect, Schiferl is analyzing how much of the change is due to an increase or decrease in the city’s emissions.

Elise Gout, explains in an article of the
Earth Institute Columbia University

“For example, on a windy day, measurements of greenhouse gas levels could be lower even though the emissions are the same. And because the measurement site is far from the emission sources, the team must also consider where the air has been. Air quality measurement sites that regularly monitor carbon monoxide throughout New York and New Jersey help the team determine what was in the air before it arrived in the city. Atmospheric models that include wind speed and direction help Schiferl determine how much greenhouse gas the air might have picked up as it passed over a chimney or other emissions source.”

The objectives of Ms. Commane’s team

In the coming year, this team hopes to establish a network of sites measuring greenhouse gas concentrations around New York City, in upper New Jersey and Connecticut.

Commane’s affiliation with academia would allow it to conduct measurements in every state in the country, as environmental agencies cannot undertake this type of project.

Roisin Commane explained in an article of
Earth Institute Columbia University

“Much of the transportation and import of goods occurs in the Port of New York and New Jersey…If we are careful about how we do this, we could get a much better estimate of emissions for the greater metropolitan area. “

In the future, better estimates will allow local governments to track the effectiveness of their environmental plans. For example, last year New York City committed to an 80% reduction in GHG emissions by 2050.

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