Nitrate flux in the Arctic not following the decreasing NOx emissions in neighboring countries

February 20, 2018, Hokkaido University
The camp at Southeastern Greenland Dome for drilling the ice core and its location shown on the map. Credit: Collage provided by Shohei Hattori, Tokyo Institute of Technology

Nitrate deposits in the Arctic remains high even after the turn of the century, despite environmental policies adopted by neighboring countries in the late 20th century to cut nitrogen oxide (NOx) emissions.

Aerosols less than 2.5 micrometers are known as particulate matter (PM) 2.5 and are hazardous to human health. Large aerosol particles, on the other hand, help form sun-blocking clouds that cool the Earth's surface. Concentrations of sulfide oxide (SOx) and NOx which can form aerosols were on the rise from the Industrial Revolution of the mid-18th century to 1980, causing serious air pollution in the 1970s and 1980s.

But regulations imposed by the United States, European countries and other developed nations have led to a reduction in SOx and NOx emissions since 1990s. That said, emissions from emerging economies such as China and India have remained high so far.

The team including Yoshinori Iizuka of Hokkaido University drilled a 90-meter from the Southeastern Greenland Dome, an ice sheet dome in Greenland that has been used for research on atmospheric aerosol depositions in ice cores from 1957 to 2014. The sample was kept frozen as it was transported to a cold room at the university's Institute of Low Temperature Science in 2015. Analysis of the ice core began the following year by melting it to measure the concentration of ions such as sulfate and nitrate.

The researchers in the drilling operation (left) and the drilled samples (right). Credit: Hokkaido University

In a previous study, the team succeeded in determining the precise ages of ice core over the six decades with an accuracy of a few months. In the study published in the Journal of Geophysical Research: Atmospheres, they proposed a dating method based on matching oxygen isotope variations between ice core records and simulations using isotope-enabled climate models – the close similarity of which allowed the precise determination of the ages.

In the present study published in the same journal, the team compared sulfate and nitrate fluxes in the ice core over the four decades with SOx and NOx emissions in the air.

To investigate the sources of the chemicals preserved in the ice core, transport pathways of air masses were analyzed using a method called Backward Trajectory Analysis. The results indicated that the highest percentage of air masses came from North America, while lower but still high percentages came from Europe and Russia. The researchers multiplied each region's NOx and SO x emissions by its air-mass contributions to calculate the volumes of NOx and SOx that reached the Southeastern Greenland Dome.

Nitrate influx did not reflect the decreasing trend of NOx emissions (left) while sulfate flux well correlated with the decreasing SOx emissions (right) from neighboring countries. Credit: Hokkaido University

The results showed that the sulfate flux reflected the history of decreasing SOx emissions from neighboring countries, mainly the United States, where the researchers believe the emissions come from. In contrast, the decadal trend of nitrate flux differed from the trend of NOx emissions, which have been declining since the 1970s or 1980s. Nitrate flux in the ice core peaked in the 1990s, and levels in the 21st Century have remained higher than that those from the period from the 1960s to the 1980s, despite efforts by the United States and European countries reduce emissions.

While the cause of this discrepancy remains a mystery, the team is examining the complicated chemical changes involving NOx that occur during atmospheric transport as a possible cause. The team plans to conduct further research on this topic, as well as evaluate other chemicals preserved in the ice core.

Explore further: Greenland ice sheet carries evidence of increased atmospheric acidity

Related Stories

Well-traveled atmospheric particles, put to the test

August 3, 2016

How do you test a model simulator? Compare it to real life. That's what scientists at Pacific Northwest National Laboratory did when they compared several observational sets with a simulation of how tiny atmospheric particles ...

Recent mercury pollution on the rise, but quick to change

June 29, 2015

A Dartmouth-led study using a 600-year-old ice core shows that global mercury pollution increased dramatically during the 20th century, but that mercury concentrations in the atmosphere decreased faster than previously thought ...

Recommended for you

Evidence of earliest life on Earth disputed

October 17, 2018

When Australian scientists presented evidence in 2016 of life on Earth 3.7 billon years ago—pushing the record back 220 million years—it was a big deal, influencing even the search for life on Mars.

Arctic greening thaws permafrost, boosts runoff

October 17, 2018

A new collaborative study has investigated Arctic shrub-snow interactions to obtain a better understanding of the far north's tundra and vast permafrost system. Incorporating extensive in situ observations, Los Alamos National ...

Arctic ice sets speed limit for major ocean current

October 17, 2018

The Beaufort Gyre is an enormous, 600-mile-wide pool of swirling cold, fresh water in the Arctic Ocean, just north of Alaska and Canada. In the winter, this current is covered by a thick cap of ice. Each summer, as the ice ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.