2.9 Nitrogen Content in Seasonal Snow Covers in the Himalayas as
consequence of the Asian Brown Cloud – Preliminary Study of the
Possibility of ReNOxification.
C.N.R. – Istituto Inquinamento Atmosferico (IIA)
Principal investigator: Dr. Beine Harry
Introduction
Human activities have overloaded the nitrogen bio-geochemical cycle by 300% of the natural
background value with nitrogen oxides (NOx) and gaseous ammonia. The main
anthropogenic NOx sources are transportation, energy production, industrial processes and
agriculture. Overloading of the nitrogen cycle has caused serious ecosystem pollution and
human health problems, including photochemical smog, acid deposition, greenhouse
effects, and stratospheric ozone depletion.
In Asia, specifically, well-aged plumes of industrial pollution and biomass burning form the
great Indo-Asian haze, also called “Asian Brown Cloud”. This cloud contains sulfates,
nitrates, nitrogen reservoir species (NOy), such as peroxyacetynitrate (PAN), and organic
species, as well as other chemicals. This cloud is mostly recognized as an aerosol problem,
which affects visibility, and, through radiative forcing, the climate.
The character and impact of chemicals in this transboundary pollution problem was first
assessed in the Indian Ocean Experiment (INDOEX). High pollution levels from agricultural
burning and biofuel extend over the entire Northern Indian Ocean. The combination with
fossil fuel combustion causes a very high aerosol load. The main chemical components in
both the coarse and fine aerosol farction are sulfates, organics and black carbon. Nitrates
are present in the coarse aerosol fractions; their impact onto snow surfaces have not been
studies yet. The nitrate concentration for example in rainwater is increasing by 30%/year
since measurements were started in 1976, similar increases are naturally expected in snow.
The impact of the ‘Brown Cloud’ to the pristine regions of the Himalayas may be compared
to that of Arctic Haze to the high Arctic.
This Brown Cloud is transported over long
distances and across national and natural borders. It carries pollution along the slopes of
the Himalayas into the free troposphere, and deposits species such as nitrates and sulfates
onto pristine snow surfaces.
On the snow surfaces the deposited nitrates will under certain conditions be liberated as
NOx and HONO. This important nitrogen re-emissions source was only recently discovered:
the re-activation of nitrate in snow surfaces and the subsequent photochemical production
of NOx and HONO (ReNOxification). The basic mechanism of this process has been
investigated in recent international projects in the Arctic. The following cartoon shows the
basic mechanism working on snow surfaces:
The possible effects of this reaction cycle are fivefold, and coupled:
1. the re-activation of nitrate essentially enhances the lifetime of active nitrogen far beyond
the few days that are generally accepted as NOx lifetime. Thus increasing by far the range
that NOx may impact atmospheric photochemistry.
2. as a result, ozone tropospheric production may increase considerably. It is conceivable
that the nitrate re-activation process may contribute to the springtime O 3 maximum in
northern latitudes.
3. also, nitrogen deposition over snow surfaces would be smaller than commonly thought.
4. the production of OH radicals from either direct photolysis of NO 3 or released HONO
may in remote regions surpass OH production from O 3 photolysis. This also would have
serious consequences on the oxidative capacity of the troposphere, and the ability to clean
pollutants from the atmosphere.
5. the reactivation of NO3 is apparently coupled with a reactivation of snowpack organic
matter and will release organics, such as aldehydes, to the atmosphere.
The proposed study is understood as a preliminary step in understanding whether
reNOxification may occur also in the pristine seasonal snow covers of the Himalayas. In the
Arctic considerable differences are present between the snow ion contents, snow surface
areas, and salinity from one site to another.
These differences decide whether the
reactivation of NOx and HONO does occur or not. For example, at Alert, Nunavut, snow
surfaces were found to be an abundant source of NOx, whereas at Ny-Ålesund, in the
Norwegian high Arctic, salinity and temperatures of the snow suppress any emission of
NOx.
It was found that the mobility of NO 3- anions in the snow surface is a determining factor for
the emission of active nitrogen. Thus, if the mobility is low, NO 3- stays confined to subsurface layers of the snow, and even with abundant UV insolation no emission of NOx or
HONO occurs.
This proposed research project thus aims to investigate the nitrogen (and other ionic
species) content of Himalayan snow in the surface and in the sub-layers of the seasonal
snow pack over a time period of a few weeks, and derive the mobility of anions in these
snowlayers. The goal is to predict the possibility of ReNO xification.
Objectives
The specific objectives of this research project are to
1. investigate whether Re-NOxification may occur in Himalayan snow.
2. Assess the impact of the Asian Red Cloud on snow surfaces around the Pyramid
To accomplish these research objectives, we have the following work objectives in a 2-year
program.
1st Year:

Sample surface and sub-layer snow in the clean-air sector around the ‘Piramide’
station over a time period of 3 – 4 weeks on a fixed measurement schedule to
capture spatial and temporal trends.

Measure the ionic content of snow for both anions and cations with a special focus
on nitrogen compounds within 12 hours of sampling to avoid storage artefacts.

Derive nitrogen budgets (and those of other ionic species) and ionic balances (i.e.
snow-pH) for all measured layers and times. Derive ionic mobilities from these
measurements.

Correlate the snow chemistry to meteorology and UV light to derive whether
ReNOxification of nitrates in the surface snow layer may occur.

Combine the information and assess whether the Asian Brown Cloud reaches free
tropospheric air at the Pyramid. If that is the case, during the second year we will
measure the actual atmosphere with a larger program using small diffusion
denuders
2nd Year:

Measure pollutants in gas and particulate phases by diffusion denuder with special
focus on nitrogen species

Collect air samples at two different heights above the snow surface around the
‘Pyramid’ station over a time period of 5 – 6 weeks to investigate concentration
differences

Analyse the ionic content of air samples for both anions and cations within 12 hours
of sampling to avoid storage artefacts.

Identify the sources of NO3- in the snow and assess whether the Asian Brown Cloud
reaches free tropospheric air at Pyramid.
Work & Time Plan
Time Schedule; the actual project is 2 year, during the calendar years of 2004 and 05