AI News, BOOK REVIEW: Salty snow could affect air pollution in the Arctic

Salty snow could affect air pollution in the Arctic

The Arctic's wintertime ice hit a record low this year, and its air is warming, according to NASA.

James Donaldson, Karen Morenz and colleagues took a closer look at how salt and nitrate content in snow could affect the levels of nitrogen oxides in the air during sunny conditions.

They found that under simulated sunlight, about 40 to 90 percent more nitrogen dioxide (NO2) was reformed from the snow with low levels of salt at environmentally relevant concentrations than snow with no salt.

Salty snow could affect air pollution in the Arctic

Previous research has shown that pollutants, including gaseous nitrogen oxides and ozone, have at times been recorded at levels similar to those one would see in more populated areas.

James Donaldson, Karen Morenz and colleagues took a closer look at how salt and nitrate content in snow could affect the levels of nitrogen oxides in the air during sunny conditions.

They found that under simulated sunlight, about 40 to 90 percent more nitrogen dioxide (NO2) was reformed from the snow with low levels of salt at environmentally relevant concentrations than snow with no salt.

The results suggest that sea ice and salty snow, which previously have not been considered as factors in the balance of ozone-forming chemicals in the atmosphere, should be a part of future models.

Salty snow could affect air pollution in the Arctic

The Arctic's wintertime ice hit a record low this year, and its air is warming, according to NASA.

Previous research has shown that pollutants, including gaseous nitrogen oxides and ozone, have at times been recorded at levels similar to those one would see in more populated areas.

James Donaldson, Karen Morenz and colleagues took a closer look at how salt and nitrate content in snow could affect the levels of nitrogen oxides in the air during sunny conditions.

DOI: 10.1021/acs.jpca.6b06685 Abstract Nitrate photolysis from snow can have a significant impact on the oxidative capacity of the local atmosphere, but the factors affecting the release of gas-phase products are not well understood.

Here, we report a systematic study of the amounts of NO, NO2, and total nitrogen oxides (NOy) emitted from illuminated snow samples as a function of both nitrate and total salt (NaCl and Instant Ocean) concentration.

The results provide experimental evidence that the release of nitrogen oxides to the gas phase is directly related to the expected nitrate concentration in the brine at the surface of the snow crystals.

In addition, for these frozen mixed nitrate (25 mM)–salt (0–500 mM) solutions, there is an increase in gas-phase NO2 seen at low added salt amounts, with NO2 production enhanced by up to 42% at low prefreezing [NaCl] (≤25 mM) and by up to 89% at prefreezing Instant Ocean concentrations lower than 200 mM [Cl–].

Sea Salts Could Be Causing Air Pollution in the Arctic

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The researchers simulated sunlight and found that about 40 to 90 percent more nitrogen dioxide (NO2) was reformed from the snow that had low levels of salt at environmentally relevant concentrations than the snow with no salt.

Ice sheets and nitrogen

First, considering nitrate and starting with Arctic records, several records covering the last century have been published from both Greenland and the nearby Canadian Arctic [14–17].

All records show an increase in concentration during the twentieth century, with the strongest slope from approximately 1950 to 1980 (examples from north and central Greenland are shown in figure 2).

They found that there had been an approximately fivefold increase in summer nitrate concentration over the last century, with the strongest rate of increase between 1960 and 1980, in agreement with at least one estimate [29] of emissions from France, Italy, Switzerland and Spain (WE4 nations).

The atmospheric flow suggests that the main sources to this site are from the west, and the increase appears consistent with the inventory trends in regional emissions from central and southwest Asia (semicircle of countries from Pakistan to Kazakhstan).

At the eastern end of the Himalayas, the situation is less clear: nitrate concentrations have increased significantly over recent decades compared with their 1000-year background at Dasuopu (7000 m.a.s.l.) [31], but the data resolution is insufficient to give a clear timing or magnitude of any increase.

Finally in Asia, an ice core further north, at Belukha in the Siberian Altai (4062 m.a.s.l.) shows a convincing increase (factor close to 2) between 1950 and 1980 [33], although this sits on a very noisy background.

For this core, as for some of the other non-polar ice cores where the combination of latitude and altitude is not sufficient to ensure cold summers, care must be taken in interpreting trends because the high percentage of melt layers in the core indicates that some percolation of water (and hence ionic load) could have occurred.

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