Subscriber access provided by Fudan University
Article
In-use emissions and estimated impacts of traditional, natural- and forced-draft cookstoves in rural Malawi Roshan Wathore, Kevin Mortimer, and Andrew P. Grieshop Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b05557 • Publication Date (Web): 06 Jan 2017 Downloaded from http://pubs.acs.org on January 8, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 26
Environmental Science & Technology
1
In-use emissions and estimated impacts of traditional, natural- and forced-draft cookstoves
2
in rural Malawi
3
Roshan Wathore1, Kevin Mortimer2, Andrew P. Grieshop1*
4
1
5
University, Raleigh, North Carolina, 27695-7908, USA
6
2
7
5QA, United Kingdom
8
* Address correspondence to: Andrew P. Grieshop, Department of Civil, Construction and Environmental
9
Engineering, North Carolina State University, 431B Mann Hall, Raleigh, NC 27696-7908, USA. Email:
10
Department of Civil, Construction and Environmental Engineering North Carolina State
Department of Clinical Sciences, Liverpool School of Tropical Medicine, Liverpool, L3
[email protected]; Ph. +1 (919) 513-1181; Fax: +1 (919) 515-7908
11 12
Abstract
13
Emissions from traditional cooking practices in low- and middle-income countries have
14
detrimental health and climate effects; cleaner-burning cookstoves may provide “co-benefits”.
15
Here we assess this potential via in-home measurements of fuel-use and emissions and real-time
16
optical properties of pollutants from traditional and alternative cookstoves in rural Malawi.
17
Alternative cookstove models were distributed by existing initiatives and include a low-cost
18
ceramic model, two forced-draft cookstoves (FDCS; Philips™ HD4012LS and ACE-1), and
19
several institutional cookstoves. Among household cookstoves, emission factors (EF; g (kg
20
wood)-1) were lowest for the Philips, with statistically-significant reductions relative to baseline
21
of 45% and 47% for fine particulate matter (PM2.5) and carbon monoxide (CO), respectively. The
22
Philips was the only cookstove tested that showed significant reductions in elemental carbon
23
(EC) emission rate. Estimated health and climate co-benefits of alternative cookstoves were
24
smaller than predicted from laboratory tests due to the effects of real-world conditions including
25
fuel variability and non-ideal operation. For example, estimated daily PM intake and field-
26
measurement-based global warming commitment (GWC) for the Philips FDCS were a factor of
27
8.6 and 2.8 times higher, respectively, than those based on lab measurements. In-field
28
measurements provide an assessment of alternative cookstoves under real-world conditions and
ACS Paragon Plus Environment
Environmental Science & Technology
29
as such likely provide more realistic estimates of their potential health and climate benefits than
30
laboratory tests.
31 32
Graphical Abstract
33 34
1.0 Introduction
35
Roughly 2.7 billion people depend on burning of biomass and other solid fuels in three stone
36
fires (TSF) and other traditional cookstoves for their day-to-day cooking purposes1. Cookstoves
37
have environmental and health impacts on an enormous scale2,3, due in large part to emissions of
38
products of incomplete combustion (PIC) such as CO, PM2.5, methane (CH4), polycyclic
39
aromatic hydrocarbons (PAHs). Black carbon (BC), commonly known as soot, is an aerosol
40
component formed during combustion estimated to have the second highest global warming
41
impact after CO2.4,5 Approximately 25% of global annual BC emissions and 60-80% of Africa’s
42
and Asia’s BC emissions that a not from open burning (e.g. wildfires) are from domestic solid
43
fuel combustion.5 BC is co-emitted with organic carbon (OC), a component which is often
44
regarded to have a cooling impact on climate6, although recent studies suggest that the OC
45
fraction (generally called brown carbon, or BrC) that absorbs radiation at short wavelengths
46
contributes significantly to warming7–9. The net climate impacts of cooking-related aerosol
47
emissions are uncertain, though likely warming.10–13 Replacement of traditional cookstoves with
48
alternative technologies thus has the potential to provide considerable climate and health benefits
49
by reducing emissions and human exposures.14,15
50
Efforts to reduce these impacts have spurred the development of a range of alternative
51
cookstoves with varying configurations, levels of sophistication and performance. Models range
52
from rudimentary low-cost cookstoves often built from local materials to mass produced state-of-
53
the-art forced draft cookstoves (FDCS) which use electrically-driven fans for improved
ACS Paragon Plus Environment
Page 2 of 26
Page 3 of 26
Environmental Science & Technology
54
combustion efficiency. Using laboratory emission factors (EF; g (kg wood)-1), Grieshop et al.16
55
estimated that health (quantified as daily intake of PM2.5 for users) and climate impacts
56
(quantified as global warming commitment or GWC) of various cookstove-fuel combinations
57
can each span two orders of magnitude, with all biomass-burning cookstoves having greater
58
impacts than ‘modern' fuel stoves such as LPG and kerosene.
59
This variation across cookstoves types and the need to benchmark performance has led to the
60
development of a tier framework17, with emissions and other parameters quantified during
61
standardized laboratory testing (e.g., the water boiling test; WBT18). While laboratory testing is
62
required for benchmarking, field data indicate that laboratory tests typically greatly overestimate
63
performance relative to in-home use. For example, field PM EFs are 2-5 times higher than those
64
measured during WBT tests.19–21 This is important because benefit estimates for alternatives rely
65
on accurate estimates of real-world performance.20–22 FDCSs have the potential to greatly reduce
66
emissions via improved combustion efficiency; laboratory PM2.5 and elemental carbon (EC) EFs
67
are an order of magnitude lower than traditional stoves23,24, putting FDCSs in the highest tiers (3
68
or 4) for indoor PM emissions. However, in-field measurements of emissions from FDCS are
69
limited, report real-time BC concentrations (not EFs) and neglect other species (e.g., CO2, OC).
70
25,26
71
Carbon finance has been held up for its potential to yield co-benefits by enabling access to
72
improved cookstove technologies by poor households.27 While flagging carbon markets28,29 and
73
evidence from early efforts30 call the near-term practicality of this into question, it remains an
74
important possible source of finance. Current carbon finance methodologies include greenhouse
75
gases (GHGs) but fail to account for the climate impact of PICs such as BC, CO, OC and non-
76
methane hydrocarbons (NMHC), mainly because of the high uncertainty and variability in their
77
emissions28,31 and the differing spatial and temporal scales of their impacts relative to GHGs.32,33
78
BC dominates cookstove PIC climate impacts6,16 and has become a focus for mitigating near-
79
term climate change. In response, the Gold Standard Foundation recently developed a simplified
80
methodology34, which relies on either laboratory or (preferred) field-based emission
81
measurements, with the latter collected using the Kitchen Testing Protocol (KPT)35, to
82
incentivize BC mitigation efforts. However, the Gold Standard does not require field emission
83
measurements to be made (only measurements of fuel use reductions)28 and as noted above few
ACS Paragon Plus Environment
Environmental Science & Technology
84
cookstoves have actually been measured in the field. Therefore, an important missing piece is a
85
rigorous understanding of in-situ emissions from cookstove technologies and the extent to which
86
the emission reductions indicated by laboratory testing are achieved under real-world conditions.
87
In response, we conducted an evaluation of in-field emissions in Malawi, Africa focusing on two
88
pre-existing cookstove programs. The specific objectives of this work were: 1) to measure fuel
89
use and emission factors from in-home use of alternative and baseline household and
90
institutional cooking technologies; 2) compare emission factors and rates with existing
91
measurements and emission ‘tiers’; 3) analyze real-time optical properties (absorption and
92
scattering) of aerosols during in-home use; 4) estimate and compare health and climate
93
impacts/benefits suggested by lab and field-based measurements.
94 95
2.0 Methods
96
2.1 Study site details - Malawi
97
Malawi is a small, landlocked country in south-eastern Africa in which over 90% of the
98
population uses biomass as their main source of domestic energy.36,37 It is one of the most
99
densely populated countries in Sub-Saharan Africa and amongst the poorest in the world, ranking
100
173 among 188 countries in Human Development Index.38 High poverty rates, dependence on
101
unsustainably-harvested firewood and a predominantly rural population means there is a great
102
need for improvements in household energy systems and makes Malawi an ideal location to
103
study the impacts of alternative cookstove technologies.39–41
104
Household emission measurements of uncontrolled in-home cookstove use (following the KPT
105
protocol35) took place during routine cooking activities in September-October 2015 (the hot and
106
dry season). Emission tests were completed in two communities on cookstoves at opposite ends
107
of the technology spectrum discussed above. In one, the Cooking and Pneumonia Study (CAPS;
108
www.capstudy.org) led by the Liverpool School of Tropical Medicine (LSTM), distributed
109
limited quantities of two FDCS models (Philips™ HD4012LS and ACE-1; cost ~90 USD) as
110
part of pilot activities for this community-level randomized controlled trial of the effects of the
111
Philips™ HD4012LS cookstove on the incidence of pneumonia in children under the age of 5.42
112
FDCS use was not widespread in this community; on the order of 10-20 cookstoves had been
ACS Paragon Plus Environment
Page 4 of 26
Page 5 of 26
Environmental Science & Technology
113
distributed. In the other, the non-governmental organization (NGO) Concern Universal (CU;
114
www.concern-universal.org) helped establish nearly-universal distribution of the Chitetezo
115
Mbaula (CM) cookstove, a low-cost (~1-2 USD), locally-produced, natural-draft clay cookstove,
116
with the main objective of reducing fuel use by users and with funding from the sale of carbon
117
credits43. In both communities, traditional three stone fires or simple mud stoves (here grouped
118
together as ‘Traditional’) were in use by some households and were also tested. Cookstoves are
119
shown in Figure S1 in the online supporting information (SI). In-home cookstove use included
120
cooking of traditional foods such as Nsima (a corn-flour porridge, the staple food of Malawi) or
121
rice, preparing vegetables or meat and heating water for bathing, and took place inside, in semi-
122
covered verandas and outside.
123
In addition to in-home testing, Controlled Cooking Tests (CCT)44 were conducted on several
124
larger, wood-burning institutional cookstoves being piloted at an orphanage. Institutional
125
cookstoves are used where a large number of people are fed; they are much larger than
126
household cookstoves to accommodate a dedicated, large cooking pot (80-100 L) that sits inside
127
the stove body, enabling more efficient heat transfer. Institutional cookstoves tested included a
128
large institutional three stone fire (I-TSF), Aleva (AL), Mayankho (MA) and the JumboZama
129
(JZ). The JumboZama is a scaled-up version of the Zama Zama rocket gasifier cookstove
130
(Rocket Works, Durban, South Africa) built inside a masonry housing. Figure S2 (SI) shows the
131
institutional cookstoves tested and Table S1 summarizes tests conducted during the campaign.
132
2.2 Sampling Methodology
133
In-home emission measurements were performed using the portable Stove Emissions
134
Measurement System (STEMS; Figure S3 in SI), which utilizes the ‘sensor board’ from a
135
Portable Emission Measurement System (Aprovecho Research, Cottage Grove, OR). The
136
STEMS runs on a 12V battery and measures real-time (2 second) concentrations of carbon
137
dioxide (CO2), carbon monoxide (CO), temperature, relative humidity (RH) and particle light
138
scattering (Bsp; also used as a proxy for real-time PM2.5 mass concentration) with a laser
139
photometer (optical wavelength, λ = 635 nm). Real-time STEMS data were logged via a laptop.
140
Integrated filter samples were collected on two 47 mm diameter filter trains with equal flows for
141
gravimetric and thermo-optical OC/EC Analysis (See SI for details). One of the filter trains
142
contained a quartz filter and the other contained a Teflon filter followed by a backup quartz filter
ACS Paragon Plus Environment
Environmental Science & Technology
143
downstream to correct for gas phase absorption artifacts.45 Additional details on the STEMS
144
sensors, filter analysis and associated uncertainties, and quality assurance are provided in Section
145
S1 in the SI.
146
Real-time PM light absorption at λ = 880 nm was measured using an AE-51 MicroAeth
147
(AethLabs) incorporated within STEMS. To avoid excessive filter loadings and frequent filter
148
ticket changes in the field, an external flow meter (Honeywell AWM3150V) and vacuum source
149
were used in place of the internal pump and flow rate set at 10-25 cm3 min-1. The MicroAeth
150
filter loading artifact was corrected via the algorithm described by Park et al.46 Additional details
151
are described in SI Section S2.
152
A six-armed stainless-steel probe with sampling ports radially-centered in equal areas was used
153
to capture a representative sample of naturally-diluted emissions approximately 1-1.5 m above
154
the cookstove.47 From the probe, emissions passed through conductive sampling tubing to the
155
STEMS via a 2.5 µm cut-point cyclone (BGI Inc.). Background air was sampled for 5-10
156
minutes before and/or after each cooking session. Wood fuel was set aside before the start of
157
cooking and wood moisture and weight recorded as per the KPT protocol.35 Wood moisture
158
content was measured with an electronic moisture meter (Lignomat mini-Ligno S/DC). Wood
159
weight before and after cooking were used to determine wood consumed. The fire was started
160
using matches or hot charcoal left from a previous cooking session; the latter practice was more
161
common. It was not feasible to weigh starting or leftover char during the study. 1 kg of wood can
162
result in up to 161 grams of char being formed.48 Neglecting starting char likely biases high the
163
estimates of wood consumed, whereas neglecting left-over char results in a low bias to wood
164
consumed. To account for this, we assume a conservative 20% uncertainty in wood consumed. A
165
brief, anonymous survey was conducted after testing to collect user feedback on performance
166
and perception of alternative cookstoves.
167
2.3 Emission Factor and Emission Rate calculations
168
Fuel based emissions factors were calculated using the carbon balance method, assuming that
169
carbon comprises 50% of dry wood by weight and all gaseous carbon in the wood is emitted as
170
CO and CO2. Since the summed carbon mass obtained from background-corrected CO and CO2
171
concentrations serves as a tracer for the fuel consumed, the carbon balance does not require all
172
emissions to be captured. Other carbonaceous species (e.g. gaseous hydrocarbons) contribute a
ACS Paragon Plus Environment
Page 6 of 26
Page 7 of 26
Environmental Science & Technology
173
relatively small fraction (
