<s>
A	O
nitrogen	B-Algorithm
oxide	I-Algorithm
sensor	I-Algorithm
or	O
sensor	O
is	O
typically	O
a	O
high-temperature	O
device	O
built	O
to	O
detect	O
nitrogen	O
oxides	O
in	O
combustion	O
environments	O
such	O
as	O
an	O
automobile	O
,	O
truck	O
tailpipe	O
or	O
smokestack	O
.	O
</s>
<s>
Many	O
governments	O
around	O
the	O
world	O
have	O
passed	O
laws	O
to	O
limit	O
their	O
emissions	O
(	O
along	O
with	O
other	O
combustion	O
gases	O
such	O
as	O
SOx	B-Operating_System
(	O
oxides	O
of	O
sulfur	O
)	O
,	O
CO	O
(	O
carbon	O
monoxide	O
)	O
and	O
CO2	O
(	O
carbon	O
dioxide	O
)	O
and	O
hydrocarbons	O
)	O
.	O
</s>
<s>
Therefore	O
,	O
in	O
many	O
applications	O
with	O
exhaust-gas	O
treatment	O
systems	O
,	O
one	O
NOx	B-Algorithm
sensor	I-Algorithm
is	O
used	O
upstream	O
of	O
the	O
exhaust-gas	O
treatment	O
system	O
(	O
upstream	O
)	O
and	O
a	O
second	O
sensor	O
is	O
used	O
downstream	O
of	O
the	O
exhaust-gas	O
treatment	O
system	O
.	O
</s>
<s>
To	O
get	O
a	O
signal	O
from	O
the	O
sensor	O
a	O
pair	O
of	O
high-temperature	O
electrodes	O
such	O
as	O
noble	O
metals	O
(	O
platinum	B-Operating_System
,	O
gold	O
,	O
or	O
palladium	O
)	O
or	O
other	O
metal	O
oxides	O
are	O
placed	O
onto	O
the	O
surface	O
and	O
an	O
electrical	O
signal	O
such	O
as	O
the	O
change	O
in	O
voltage	O
or	O
current	O
is	O
measured	O
as	O
a	O
function	O
of	O
concentration	O
.	O
</s>
<s>
In	O
addition	O
due	O
to	O
the	O
harsh	O
environment	O
of	O
combustion	O
the	O
high	O
gas	O
flow	O
rate	O
can	O
cool	O
the	O
sensor	O
which	O
alters	O
the	O
signal	O
or	O
it	O
can	O
delaminate	O
the	O
electrodes	O
over	O
time	O
and	O
soot	B-Language
particles	O
can	O
degrade	O
the	O
materials	O
.	O
</s>
<s>
High	O
amount	O
of	O
cross	O
sensitivity	O
has	O
been	O
observed	O
in	O
gas	O
sensors	O
due	O
to	O
similarity	O
in	O
electron	B-General_Concept
exchange	I-General_Concept
mechanism	O
between	O
target	O
gases	O
and	O
water	O
molecules	O
.	O
</s>
