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    Ristovski, Zoran and Wardoyo, Arinto Y. P. and Morawska, Lidia and Jamriska, Milan and Carr, Stephen and Johnson, Graham R. (2010) Biomass burning influenced particles characteristics in Northern Territory Australia based on airborne measurements. Atmospheric Research, 96(1). pp. 103-109.

    © Copyright 2010 Elsevier

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    Biomass Burning Influenced Particles Characteristics in Northern Territory Australia Based on Airborne

    Measurements 1Zoran D. Ristovski*, 1,3Arinto Y.P. Wardoyo, 1Lidia Morawska, 2Milan Jamriska,

    2Stephen Carr and 1Graham Johnson.

    1International Laboratory for Air Quality and Health (ILAQH) Queensland University of Technology,

    GPO Box 2434, Brisbane, Queensland 4001, Australia. 2 Defence Science and Technology Organisation (DSTO)

    3Physics Department, Brawijaya University, Malang, Indonesia.

    *Corresponding Author: Phone +61 7 3138 1129; Email: z.ristovski@qut.edu.au Abstract Airborne measurements of particle number concentrations from biomass burning were

    conducted in the Northern Territory, Australia, during June and September campaigns in

    2003, which is the early and the late dry season in that region. The airborne

    measurements were performed along horizontal flight tracks, at several heights in order

    to gain insight into the particle concentration levels and their variation with height within

    the lower boundary layer (LBL), upper boundary layer (UBL), and also in the free

    troposphere (FT). The measurements found that the concentration of particles during the

    early dry season was lower than that for the late dry season. For the June campaign, the

    concentration of particles in LBL, UBL, and FT were (685 ± 245) particles/cm3, (365 ±

    183) particles/cm3, and (495 ± 45) particle/cm3 respectively. For the September

    campaign, the concentration of particles were found to be (1233 ± 274) particles/cm3 in

    the LBL, (651 ± 68) particles/cm3 in the UBL, and (568 ± 70) particles/cm3 in the FT.

    The particle size distribution measurements indicate that during the late dry season there

    was no change in the particle size distribution below (LBL) and above the boundary layer

    (UBL). This indicates that there was possibly some penetration of biomass burning

    particles into the upper boundary layer. In the free troposphere the particle concentration

    and size measured during both campaigns were approximately the same.

    Keywords: Biomass burning, particle number concentration, Northern Territory Australia,

    airborne measurements.

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    1. Introduction

    Biomass burning, including forest fires, agricultural waste burning, prescribed wild land

    burning, logging and land clearing slash, and burning for cooking and heating, has been

    identified as a major contributor of particles in the atmosphere (Areskoug, Camner et al.

    2000; Dennis, Fraser et al. 2002; Uherek 2004). Previous studies have shown that most of

    the particles from biomass burning were found to be of a size less than 1 μm in diameter

    (Ferge, Maguhn et al. 2005; Reid, Koppmann et al. 2005; Wieser and Gaegauf 2005) and

    that their presence in the air significantly affects atmospheric processes (Shaw 1987). The

    effects range from acidification of clouds, rain, and fog (Nichol 1997); altering cloud

    microphysical processes in a small scale and mesoscale; and altering the radiation

    balance of the earth, both directly, by absorbing and scattering incoming solar radiation,

    and indirectly, by acting as cloud condensation nuclei (CCN) (Kaufman, Hobbs et al.

    1998; Martins, Artaxo et al. 1998; Wurzler and Simmel 2005).

    Numerous studies investigated characteristics of particle from biomass burning in several

    regions, such as Africa (Anderson et al, 1996; Dubovik et al, 2002, Haywood et al,2003a,

    Eck et al, 2003), North America (Hobbs el al, 1996, Radke et al, 1991, Dubovik et al,

    2002), Eck el al, 2003), South America (Anderson et al,1996, Andreae et al, 1988,

    Dubovik et al,2002, Echalar et al, 1998, Eck et al, 2003, Reid et al, 1998b), and

    meditarian (Formenti et al, 2002). The reports showed that biomass burning particles

    found in different region vary in concentrations, emission factors, and sizes. The variety

    of particle characteristics may be due to several factors such as: intensity of fires, fuel

    types, moisture, weather condition, and other variables.

    Very few airborne measurements of atmospheric aerosols have been conducted over the

    continent of Australia, with one study conducted only in the Eastern part of the continent

    (Gras 1991) and a few other campaigns focused on characterizing the biomass burning

    plumes in both the Northern Territory and parts of Indonesia (Borneo) (Gras 1999;

    Tsutsumi 1999). Considering the size of Australia and the scale of biomass burning that

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    occurs annually, both as controlled and uncontrolled burning, there is a need to gain a

    better quantitative insight into the biomass burning emissions in this region. Such

    information is essential in developing better understanding of the potential impacts of the

    emissions as well as input into climate change forecasting models (Rotstayn, Cai et al.

    2007). To address this need a large program was undertaken involving Queensland

    University of Technology (QUT), the Defense Science and Technology Organization

    (DSTO), and the Australian Commonwealth Scientific and Industrial Research

    Organization (CSIRO), with the main focus on characterizing biomass burning aerosols

    in the Northern Territory, Australia, during the 2003 dry season. The specific objective of

    the part of work reported here was to conduct measurements of particle size and number

    concentration at different heights to provide an insight into the impact of biomass burning

    on the vertical particle profiles. Other characteristics of aerosol such as chemical and

    optical characteristics (Carr, Gras et al. 2005) and size distribution (Wardoyo, Morawska

    et al. 2007) were reported elsewhere.

    2. Experimental Methods

    2.1. Study Area

    The study was conducted over the large areas of tropical savannas of the Northern

    Territory, Australia. The dominant vegetation type of these savannas is a mixture of

    annual grasses, such as Sorghum species and perennial grasses, and tropical savanna

    woodland, made up of sporadic trees, predominantly the Eucalyptus miniatia (Wilson,

    Brocklehurst et al. 1990; Williams, Cook et al. 1999). A large fraction of the vegetation is

    burnt annually by naturally occurring fires (Russell-Smith, Ryan et al. 1997).

    The climate in the savanna region of the Northern Territory is highly seasonal and has a

    distinctive dry and wet season. The wet season is hot and humid, occurring from

    November to April. The entire average annual precipitation, of over 1000 mm, nearly

    always occurs during this period. The rainfall pattern for the region varies greatly from

    year to year due to the Southern oscillation (McKeon, Day et al. 1990). In comparison,

    the dry season is mild to warm and extends from May to October. Naturally biomass

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    burning occurs during almost every dry season (Gill, Ryan et al. 2000). These fires are

    usually of a mild intensity in the early dry season (EDS) and of a high intensity in late dry

    season (LDS) (Williams, Gill et al. 1998).

    2.2. Measurement Times and Locations

    The airborne measurements of particle number concentration and particle size

    distribution were conducted during two campaigns, in June and September 2003, which

    were in the EDS and the LDS, respectively. The measurements were performed both in

    the morning and in the afternoons with the duration of each flight leg from 20 to 30

    minutes. The total time spent for each measurement for every flight was approximately

    four hours. This included transit from Darwin to on station, a vertical stack of horizontal

    flight legs and return transit to Darwin. In June the flights were on the Monday, Tuesday

    and Thursday afternoons with the final flight on the Friday morning. In September

    campaign, the fights were conducted two times in the morning (Tuesday and Thursday)

    and two in the afternoon (Monday and Friday).

    The airborne measurements were carried out along a predetermined horizontal path, that

    extended from a point South West (SW) of Jabiru (13.08 South (S) 132.32 East (E)) to a

    point North East of Jabiru (12.11 S 133.15 E), in Kakadu National Park, Northern

    Territory. The orientation of the flight path was chosen so that the flight track was

    perpendicular to prevailing wind directions on the ground. The wind was predominantly

    coming from the South East (SE) during the June campaign and from the North West

    (NW) during the September campaign. The wind direction did vary somewhat from day

    to day and from morning to afternoon, however the variation was in general not

    significant enough to influence the choice of the predetermined flight direction. Figure 1

    presents a map of Australia with the enlarged top end of the North