Speciated online PM1 from South Asian combustion sources – Part 1: Fuel-based emission factors and size distributions
Authors: Goetz J. Douglas , Giordano Michael R. , Stockwell Chelsea E. , Christian Ted J. , Maharjan Rashmi , Adhikari Sagar , Bhave Prakash V. , Praveen Puppala S. , Panday Arnico K. , Jayarathne Thilina , Stone Elizabeth A. , Yokelson Robert J. , DeCarlo Peter F. 
Published: October 2018

Abstract. Combustion of biomass, garbage, and fossil fuels in South Asia has led to
poor air quality in the region and has uncertain climate forcing impacts.
Online measurements of submicron aerosol (PM1) emissions were conducted
as part of the Nepal Ambient Monitoring and Source Testing Experiment
(NAMaSTE) to investigate and report emission factors (EFs) and vacuum
aerodynamic diameter (dva) size distributions from prevalent but
poorly characterized combustion sources. The online aerosol instrumentation
included a “mini” aerosol mass spectrometer (mAMS) and a dual-spot
eight-channel aethalometer (AE33). The mAMS measured non-refractory PM1
mass, composition, and size. The AE33-measured black carbon (BC) mass and
estimated light absorption at 370 nm due to organic aerosol or brown
carbon. Complementary gas-phase measurements of carbon dioxide (CO2),
carbon monoxide (CO), and methane (CH4) were collected using a
Picarro Inc. cavity ring-down spectrometer (CRDS) to calculate fuel-based EFs
using the carbon mass balance approach. The investigated emission sources
include open garbage burning, diesel-powered irrigation pumps, idling
motorcycles, traditional cookstoves fueled with dung and wood, agricultural
residue fires, and coal-fired brick-making kilns, all of which were tested in
the field. Open-garbage-burning emissions, which included mixed refuse and
segregated plastics, were found to have some of the largest PM1 EFs
(3.77–19.8 g kg−1) and the highest variability of the investigated
emission sources. Non-refractory organic aerosol (OA) size distributions
measured by the mAMS from garbage-burning emissions were observed to have
lognormal mode dva values ranging from 145 to 380 nm.
Particle-phase hydrogen chloride (HCl) was observed from open garbage
burning and was attributed to the burning of chlorinated plastics. Emissions
from two diesel-powered irrigation pumps with different operational ages were
tested during NAMaSTE. Organic aerosol and BC were the primary components of
the emissions and the OA size distributions were centered at ∼80 nm
dva. The older pump was observed to have significantly larger
EFOA than the newer pump (5.18 g kg−1 compared to
0.45 g kg−1) and similar EFBC. Emissions from two distinct
types of coal-fired brick-making kilns were investigated. The less advanced,
intermittently fired clamp kiln was observed to have relatively large EFs of
inorganic aerosol, including sulfate (0.48 g kg−1) and ammonium
(0.17 g kg−1), compared to the other investigated emission sources.
The clamp kiln was also observed to have the largest absorption
Ångström exponent (AAE = 4) and organic carbon (OC) to BC ratio
(OC : BC = 52). The continuously fired zigzag kiln was
observed to have the largest fraction of sulfate emissions with an
EFSO4 of 0.96 g kg−1. Non-refractory aerosol size
distributions for the brick kilns were centered at ∼400 nm
dva. The biomass burning samples were all observed to have
significant fractions of OA and non-refractory chloride; based on the
size distribution results, the chloride was mostly externally mixed from the
OA. The dung-fueled traditional cookstoves were observed to emit ammonium,
suggesting that the chloride emissions were partially neutralized. In
addition to reporting EFs and size distributions, aerosol optical properties
and mass ratios of OC to BC were investigated to make comparisons with other
NAMaSTE results (i.e., online photoacoustic extinctiometer (PAX) and off-line
filter based) and the existing literature. This work provides critical field
measurements of aerosol emissions from important yet under-characterized
combustion sources common to South Asia and the developing world.