write:The ionic species NO2− NO3− and NH4+ are found in the aqueous phase. Nitrogen is the most abundant gas in the atmosphere. Under ambient conditions it is relatively unreact

NO
NO2
nitrate radical (NO3·)
dinitrogen pentoxide (N2O5)
HNO2
nitric acid (HNO3)
organic nitrates such as peroxyacyl nitrate (CH3COO2NO2)
i.e.
PAN
and reduced N compounds such as NH3 and hydrogen cyanide (HCN). The ionic species
NO2−
NO3−
and NH4+
are found in the aqueous phase. Nitrogen is the most abundant gas in the atmosphere. Under ambient conditions
it is relatively unreactive and plays no direct role in atmospheric chemistry. However
as a result of combustion reactions and biological processes
it serves as a precursor molecule for production of NO and NO2
which play significant roles in tropospheric and stratospheric chemistry. Because they are readily converted from one to the other
NO and NO2 concentrations are expressed as NOx. Reactive nitrogen (NOy) includes NOX compounds as well as their atmospheric oxidation products
e.g.
HNO2
HNO3
NO3·
N2O5
peroxynitric acid (HNO4)
PAN and its homologues
alkyl nitrates (RONO2)
and peroxyalkyl nitrates (ROONO2). Total NOy is a measure of the total oxidized N content of the atmosphere. Despite relatively low concentrations
NO
NO2
organic nitrates
gas- and particulate-phase N acids
and NH3 play significant roles in atmospheric chemistry (particularly in polluted environments). Nitric oxide and NO2 are of major environmental concern since atmospheric concentrations increase significantly as a result of human activities
and they serve as precursor molecules for many important atmospheric reactions. 2.3.3.1 Nitrous Oxide Nitrous oxide is a colorless
slightly sweet
relatively nontoxic gas. It is widely used as an anesthetic in medicine and dentistry. Human exposure to elevated concentrations produces a kind of hysteria
and as such
it is often referred to as laughing gas. Nitrous oxide concentrations in the atmosphere have been increasing steadily since preindustrial times
from ~280 to ~320 ppbv today. Estimated annual emissions to the atmosphere are 13.8 Tg (tetragrams) N/year
with ~70% being produced by nitrification and denitrification processes in undisturbed terrestrial environments and the world’s oceans. About 3 Tg N/year
or ~8%
is associated with agricultural tillage
fertilizer use
and animal wastes. Nitrous oxide has no known tropospheric sink. As a result
it has a very long atmospheric lifetime (~150 years). Its photolysis and subsequent oxidation by singlet oxygen (O(1D)) in the stratosphere is the only known sink process. As such
N2O is the major natural source of NOx in the stratosphere
where it plays a significant role in stratospheric O3 chemistry. Increased atmospheric N2O levels pose two major environmental concerns: stratospheric O3 depletion and
because of its thermal absorptivity
global warming (see Chapter 4). Air quality 42