The atmospheric chemistry of trace gases and particulate matter emitted by different land uses in Borneo

Abstract

We report measurements of atmospheric composition over a tropical rainforest and over a nearby oil palm plantation in Sabah, Borneo. The primary vegetation in each of the two landscapes emits very different amounts and kinds of volatile organic compounds (VOCs), resulting in distinctive VOC fingerprints in the atmospheric boundary layer for both landscapes. VOCs over the Borneo rainforest are dominated by isoprene and its oxidation products, with a significant additional contribution from monoterpenes. Rather than consuming the main atmospheric oxidant, OH, these high concentrations of VOCs appear to maintain OH, as has been observed previously over Amazonia. The boundary-layer characteristics and mixing ratios of VOCs observed over the Borneo rainforest are different to those measured previously over Amazonia. Compared with the Bornean rainforest, air over the oil palm plantation contains much more isoprene, monoterpenes are relatively less important, and the flower scent, estragole, is prominent. Concentrations of nitrogen oxides are greater above the agro-industrial oil palm landscape than over the rainforest, and this leads to changes in some secondary pollutant mixing ratios (but not, currently, differences in ozone). Secondary organic aerosol over both landscapes shows a significant contribution from isoprene. Primary biological aerosol dominates the super-micrometre aerosol over the rainforest and is likely to be sensitive to land-use change, since the fungal source of the bioaerosol is closely linked to above-ground biodiversity.

Figure 1.

The geographical region (northern Borneo) studied in OP3/ACES. Shading shows land use; white areas are predominantly oil palm plantation. The coloured dots are isoprene mixing ratios measured by the FAAM BAe146 research aircraft flying when in the boundary layer. The strong black line shows the path usually taken by the BAe146 to reach Bukit Atur at low altitude, and is the section along which the measurements shown in figure 4 were made. The location of the oil palm site and the nearest urban area are shown. Adapted from fig. 1 of Hewitt et al. [31].

Figure 2.

Time-sequence of photographs from the GAW tower at Bukit Atur through a typical day.

Figure 3.

Mean vertical profiles of dry-bulb potential temperature over the rainforest (squares) and oil palm plantation (circles) landscapes from observations using the FAAM BAe146 research aircraft during OP3-III. Data are binned in 100 m bins plotted at the mid-point of the bin, and are plotted against height above ground. Horizontal bars are ± 1 s.d.

Figure 4.

The influence of land use on atmospheric composition, as shown by aircraft data in flight segments traversing plantation and rainforest at low altitude. From top to bottom panels, the quantities plotted are: isoprene mixing ratio (pptv), NO_x (pptv), CO (ppbv), acetone (pptv), peroxy acetyl nitrate (PAN, pptv), O₃ (ppbv), sulphate aerosol mass concentration (g m⁻³) and organic aerosol mass concentration (g m⁻³).

Figure 5.

Average proton-transfer reaction mass spectrometer (PTR-MS) fingerprints from (a) the rainforest at Danum and the (b) nearby Sabahmas oil palm plantation. Peaks are assigned, as discussed in the main text. Tentative assignments are given in grey. Note the different y-axes on the plots.

Figure 6.

Average diurnal cycles of VOCs targeted in the PTR-MS observations, measured at 75 m above ground at the Bukit Atur rainforest site. Grey shading and error bars show the variability (±1 s.d.) about the mean. Solid line, rainforest; circles with solid line, oil palm.

Figure 7.

Diurnal average mixing ratios of the monoterpenes camphene, limonene and γ-terpinene and the isoprene breakdown product methacrolein, as measured by gas chromatography at 5 m above ground at the Bukit Atur rainforest site.

Figure 8.

Mean hourly averaged HO₂ + ΣRO₂ diurnal cycles taken at Bukit Atur during OP3-I (Apr/May 2008) and OP3-III (June/July 2008). Diamonds with solid line, HO₂+RO₂/OP3-I; triangles with solid line, HO₂+RO₂/OP3-III.

Figure 9.

Mean day-time cycle for net rate of ozone change, N[O₃] (asterisks with solid line), ozone production rate, P[O₃] (plus symbols with solid line), and ozone loss rate, L[O₃] (triangles with solid line), from OP3-I.