Sorption of Pure N
2
O to Biochars and Other Organic and Inorganic
Materials under Anhydrous Conditions
Gerard Cornelissen,
‡,§,∥,
* David W. Rutherford,
†,
* Hans Peter H. Arp,
‡
Peter Dö rsch,
§
Charlene N. Kelly,
†
and Colleen E. Rostad
†
†
U.S. Geological Survey, Denver, Colorado 80225, United States
‡
Norwegian Geotechnical Institute (NGI), Department of Environmental Engineering, P.O. Box 3930, Ullevå l Stadion, NO-0806
Oslo, Norway
§
Department of Plant and Environmental Sciences (IPM), Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås,
Norway
∥
Department of Applied Environmental Sciences (ITM), Stockholm University, 10691 Sweden
* S Supporting Information
ABSTRACT: Suppression of nitrous oxide (N
2
O) emissions from soil is
commonly observed after amendment with biochar. The mechanisms
accounting for this suppression are not yet understood. One possible
contributing mechanism is N
2
O sorption to biochar. The sorption of N
2
O
and carbon dioxide (CO
2
) to four biochars was measured in an anhydrous
system with pure N
2
O. The biochar data were compared to those for two
activated carbons and other components potentially present in soils
uncharred pine wood and peatand five inorganic metal oxides with
variable surface areas. Langmuir maximum sorption capacities (Q
max
) for
N
2
O on the pine wood biochars (generated between 250 and 500 °C) and
activated carbons were 17−73 cm
3
g
−1
at 20 °C (median 51 cm
3
g
−1
), with
Langmuir affinities (b) of 2−5 atm
−1
(median 3.4 atm
−1
). Both Q
max
and b
of the charred materials were substantially higher than those for peat,
uncharred wood, and metal oxides [Q
max
1−34 cm
3
g
−1
(median 7 cm
3
g
−1
); b 0.4−1.7 atm
−1
(median 0.7 atm
−1
)]. This indicates that biochar can bind N
2
O more strongly than both mineral and
organic soil materials. Q
max
and b for CO
2
were comparable to those for N
2
O. Modeled sorption coefficients obtained with an
independent polyparameterlinear free-energy relationship matched measured data within a factor 2 for mineral surfaces but
underestimated by a factor of 5−24 for biochar and carbonaceous surfaces. Isosteric enthalpies of sorption of N
2
O were mostly
between −20 and −30 kJ mol
−1
, slightly more exothermic than enthalpies of condensation (−16.1 kJ mol
−1
). Q
max
of N
2
O on
biochar (50000−130000 μgg
−1
biochar at 20 °C) exceeded the N
2
O emission suppressions observed in the literature (range
0.5−960 μgg
−1
biochar; median 16 μgg
−1
) by several orders of magnitude. Thus, the hypothesis could not be falsified that
sorption of N
2
O to biochar is a mechanism of N
2
O emission suppression.
■
INTRODUCTION
Biochar is waste biomass charcoal that, due to its stability in soil,
could provide a wedge in climate change mitigation, while
simultaneously improving the fertility and quality of degraded or
polluted soils.
1
Apart from its carbon sequestration potential,
biochar has also been observed to inhibit the formation or
emission of the powerful greenhouse gas nitrous oxide
(N
2
O).
2−13
This gas is mostly formed as a nonstoichiometric
byproduct during microbial ammonia oxidation to NO
2
−
(“nitrification”), as an obligate intermediate during the
respiratory reduction of NO
3
−
to N
2
(“denitrification”), and in
the dissimilatory reduction of NO
3
−
to NH
4
+
(“DNRA”).
14,15
Yanai et al.
5
found that 10 wt-% biochar in open laboratory
incubations with soil reduced cumulative N
2
O emissions during a
168-h period by almost 90%. Spokas et al.,
6
in 100 d-batch
incubations, found N
2
O emission reductions of up to 75%. Singh
et al.
7
deployed soil columns for two soils over 150 d, and 0.8 wt-
% biochar treatments decreased N
2
O emissions by 14−73%.
Case et al.
8
found in a soil core study that cumulative N
2
O
production within 60 h of wetting was 19−98% lower in
treatments with 1−10 wt-% biochar than in a biochar-free
control. Van Zwieten et al.
10
found in batch microcosms that
amendment with 1 and 5 wt-% biochar reduced N
2
O emissions
by 50% and 80%, respectively. In field studies across China, N
2
O
emission reductions were 70%
9
(40 t ha
−1
biochar), 40%
11
(20 t
ha
−1
), and 60%
11
(40 t ha
−1
). Kammann et al.
2
found N
2
O
emission reductions up to 60% in biochar−compost systems. In
Received: February 12, 2013
Revised: May 24, 2013
Accepted: June 13, 2013
Article
pubs.acs.org/est
© XXXX American Chemical Society A dx.doi.org/10.1021/es400676q | Environ. Sci. Technol. XXXX, XXX, XXX−XXX