Acknowledgements: We gratefully acknowledge Paraiso D’Angelo and it’s owner Sr. D’Angelo, the captains and crew of the boats, and the staff from the MPI workshop. This project was funded by the Max Planck Society.

For further information please contact: Ivonne TrebsE-mail: ivonne@mpch-mainz.mpg.deTel.: 49-6131-305-306Fax: 49-6131-305-579

“Manaus Case”“Background Case”Date: 20-21 July, 2001; Location: 3.092° S, 60.197° W

Figure 1: Satellite image of the area of Manaus (Amazonia/Brazil); colored lines indicate the tracks of the boat, squares frame the specific study areas considered for the “Background case” and “Manaus case”, respectively.

Date: 09-10-11 of July, 2001; Location: 3.033° S, 61.345° W

I. Trebs(1), O. L. Mayol-Bracero(2), F.X. Meixner(1), M. O. Andreae(1), U. Rummel(1), P. Artaxo(3), A. Camargo(3), T. Pauliquevis(3), M. Richardson(4)

(1) Max Planck Institute for Chemistry, Biogeochemistry Department, Mainz, Germany, (2) Institute for Tropical Ecosystem Studies, University of Puerto Rico, San Juan, Puerto Rico, USA (3) Instituto de Física, Universidad de São Paulo, São

Paulo, Brasil (4) Universidad Federal de Alagoas, AL, Brasil

DIEL VARIATIONS OF NO, NODIEL VARIATIONS OF NO, NO22, O, O33 AND CO AND CO22 MIXING RATIOS IN A TROPICAL MIXING RATIOS IN A TROPICAL

ENVIRONMENT- OBSERVATIONS FROM A BOAT PLATFORM ON THE AMAZONENVIRONMENT- OBSERVATIONS FROM A BOAT PLATFORM ON THE AMAZON

Introduction Implementation

Figure 2: The two boat platforms navigating on Rio Negro

During the Cooperative LBA(*) AIrborne Regional Experiment 2001 (CLAIRE 2001) we measured NO, NO2, O3 and CO2 mixing ratios on a boat platform which was cruising on rivers Rio Manacapuru and Rio Negro near Manaus (Amazonia/Brazil) (see Figure 1). Within CLAIRE 2001, the main purpose of this study was to provide surface based measurements for the companion airborne investigations [see Thielmann et al., 2003] in order to study the location, the chemical composition and the temporal behavior of polluted air masses originating from the city of Manaus. Therefore, it was intended to sample (a) polluted air masses which have interacted with the rainforest and (b) “background” air from pristine rainforests. Measurements were supported by monitoring of meteorological quantities (i.e. wind speed, wind direction, relative humidity, ambient temperature), as well as the geographical position of the boat platform. Here, we present diel variations of NO, NO2, O3 and CO2 mixing ratios for two contrasting cases, the “background case” (Rio Manacapuru) and the “Manaus case” (Rio Negro).

(*)LBA = Large Scale Biosphere-Atmosphere experiment in Amazonia

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Figure 4: Distribution of wind direction during the “background case”, 09-11-JUL-2001 (calculated from individual 1 min data).

Figure 3: The boat position (white star) during the “background case”,09-11-JUL-2001 (white- framed box in Figure 1).

Figure 9: Distribution of wind direction during the “Manaus case”, 20-21-JUL-2001 (calculated from individual 1 min data).

Figure 8: The boat’s position (red star) during the “Manaus case”, 20-21-JUL-2001 (red-framed box in Figure 1).

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Figure 5: Mean diel variation of NO, NO2 and O3 mixing ratios averaged for the entire period of the “background case”, 09-11-JUL-2001 (10 min averages calculated from individual 1 min data). Detection limits (1-definition) are indicated by arrows. Gaps are caused by rejection of corresponding mixing ratios due to (a) contamination by boats and/or diesel generator and (b) meeting the “below detection limit” criterion.

Figure 6: Mean diel variation of CO2 mixing ratio and absolute humidity averaged for the entire period of the “background case”, 09-11-JUL-2001 (10 min averages calculated from individual 1 min data). Gaps are caused by rejection of corresponding mixing ratios due to contamination by boats and/or diesel generator.

Figure 7: Mean diel variation of relative humidity, air temperature and global radiation averaged for the entire period of the “background case”, 09-11-JUL-2001 (10 min averages calculated from individual 1 min data).

The measured NO, NO2, O3 and CO2 mixing ratios in this case are considered to be representative for the remote Amazonian background, since the boat’s position on Rio Manacapuru was entirely surrounded by rain forest (Figure 3) and ~130 km distant from the city borders of Manaus (Figure 1). Wind directions ranged from E to SE (Figure 4). Mixing ratios of NO and NO2 were well below 1 ppb and remained virtually constant (NO: 0.270.08 ppb; NO2: 0.640.13 ppb) during this period. In contrast, O3 mixing ratio reveals a marked diel cycle featuring ~20 ppb in the afternoon and ~8 ppb at nighttime (Figure 5). Nighttime O3 values on Rio Manacapuru were considerably higher than comparable tower-based measurements (< 3 ppb, Reserva Biologica Jaru (Rondonia/Brazil), see [Andreae et al., 2002]. This can be explained by (a) lower O3 deposition velocities [Erisman et al., 1994] and (b) less stable nocturnal thermal stratification over (still warm) water surfaces than over rainforest ecosystems, respectively.

Figure 10: Diel variation of NO, NO2 and O3 mixing ratios during the period of the “Manaus case”, 20-21-JUL-2001 (10 min averages calculated from individual 1 min data). Gaps are caused by rejection of corresponding mixing ratios due to contamination by boats and/or diesel generator. NO2 measurements are not available from 06:00 of 21 July due to instrument failure.

Figure 11: Diel variation of CO2 mixing ratio, particle scattering coefficient, and absolute humidity during the period of the “Manaus case”, 20-21-JUL-2001 (10 min averages calculated from individual 1 min data). Gaps are caused by rejection of corresponding mixing ratios due to contamination by boats and/or diesel generator.

Figure 12: Diel variation of relative humidity, air temperature and global radiation averaged for the period of the “Manaus case”, 20-21-JUL-2001 (10 min averages calculated from individual 1 min data).

Figure 13: Diel variation of wind speed and wind direction averaged for the period of the “Manaus case”, 20-21-JUL-2001 (10 min averages calculated from individual 1 min data).

In the “Manaus case” the boat platforms were located rather close (~30 km) to the city border of Manaus (Figures 1 & 8). Measurements of trace substances were strongly influenced by pollution from Manaus (via transport from the NE to SE sectors; see (Figure 9). On 20 July, we observed the usual mid-morning steep increase of O3 mixing ratio, which was suddenly interrupted at 12:00 (50 ppb 30 ppb). This event is accompanied by high NO (up to 4 ppb) and NO2 (up to 7 ppb) mixing ratios (arriving from the SE sector) indicating a “young” pollution plume (Figure 10). With the change of wind direction from SE to SW/W (20:00-21:00, 20 July, Figure 13) an obviously aged plume arrived which lasted to 03:00 on 21 July, characterized by enhanced NO2 and low NO mixing ratios, as well as high particle scattering coefficients (Figures 10 & 11). Again, around noon on 21 July, O3 mixing ratios were very high (up to 85 ppb, Figure 10).

Around 3:00 on 21 July, O3 declined to  5 ppb (Figure 10), when wind direction changed from SW/W to NW/NE sectors and wind speed nearly ceased (< 0.5 m/s) (Figure 13). Since the boat’s position was very close to the river bank, corresponding air masses were definitely of rain forest origin. Low O3 mixing ratios (due to deposition on wet surfaces, [see Gut et al., 2002] are accompanied by enhanced NO mixing ratios (around 1 ppb) which originate from biogenic soil sources and consequent accumulation in the trunk space of the rain forest [see Rummel et al., 2002]. This supports the conclusion that a “forest-river breeze” was present, which was established by relatively warm (rising) air over the river causing advection of cooler air from the rain forest.

A “forest-river breeze” on Rio Negro?!

"Background case“ and "Manaus case“ revealed marked differences in trace gas mixing ratios. "Manaus case“ was characterized by enhanced O3 and NO2 mixing ratios, up to 2-3 and 7 times higher than in the “background case”, respectively. When corresponding air masses originated from the river’s surface layer, nighttime O3 mixing ratios of ~8 to 10 ppb have been observed, which are considerably higher than those observed at nighttime over terrestrial surfaces. This behavior is attributed to lower O3 deposition velocities and less stable nocturnal thermal stratification over water surfaces than over rainforest ecosystems, respectively. From corresponding trace gas observations we found evidence for a (very local) “forest-river breeze” on Rio Negro. However, from our measurements of trace gases at the boat platform alone, origin and age of polluted air masses are difficult to assess; effects of small scale (very local) thermo-orographic wind systems have to be considered in detail.

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Two boat platforms were used during our experiment (Figure 2). The 1st (leading) boat was equipped with the analytical and sampling instrumentation, while the 2nd boat carried a diesel generator providing 15 kW for operation of the instruments. The power cable (d= 2 cm, 40 m long) was connected to an electrical manifold onboard of the 1st boat and kept on the water surface using floating devices. The 2nd boat was pulled by the 1st boat using a 5 mm steel rope and was kept always downwind of the 1st boat to minimize the risk of local contamination. The inlet for trace gas sampling was located 3 m above the water surface and meteorological quantities were measured on a mast at a height of 8 m. Sensitive chemiluminescense and NDIR analyzers (see Table 1) were applied to measure NO, NO2, O3 and CO2 mixing ratios. Extensive aerosol sampling was also performed during the entire campaign [see Mayol-Bracero et al., 2003].

Detection Type Detection limit/

Precision

NO Gas-phase chemiluminescence

CLD 780 TR (Eco Physics, Switzerland)

100± 50 ppt

NO2 Photolysis to NO, Gas-phase chemiluminescense

PLC 760/ CLD 780 TR (Eco Physics, Switzerland)

400± 150 ppt

O3 UV absorption Model 49, Thermo Environment, USA) 2± 1 ppb

CO2 IR absorption Model LI-6262, (LiCor, USA)

± 2 ppm

Table 1: Specification of the instruments applied

Rio Negro

Rio Manacapuru

61.0°W 60.5°W 60.0°W

Manaus

2.5°S

3.0°S

3.5°S

CO2 shows the expected typical diel variation: maximum values just before sunrise (> 400 ppm) and background values (~340 ppm) in the late afternoon due to dominant nighttime soil- & plant respiration and effective turbulent mixing/photosynthesis activity during daytime, respectively (Figure 6). Diel variation of air temperature, relative humidity and global radiation are characteristic for a tropical rainforest environment (Figure 7).

A similar behavior could not be observed in the previous night (00:00-06:00, 20 July), since corresponding air masses were transported from the E/NE sector (over extended water surfaces) with relatively high (nighttime) wind speeds (> 1 m/s) (Figure 13). Corresponding NO, NO2 and O3 values resemble those of the “background case” on Rio Manacapuru (Figure 5).

References: Andreae, M.O. et al. (2002): Biogeochemical cycling of carbon, water, energy, trace gases and aerosols in Amazonia: The LBA-EUSTACH experiments, Journal of Geophysical Research, 107 (D20), 8066, doi:10.1029/2001JD000524

Erisman et al. (1994): Parameterization of surface resistance for the quantification of atmospheric deposition of acidifying pollutants and ozone, Atmospheric Environment, 28

Gut, A. et al. (2002): Exchange fluxes of NO, NO2, and O3 at soil and leaf surfaces in an Amazonian rain forest, Journal of Geophysical Research, 107 (D20), 8060, doi:10.1029/2001JD000654.

Mayol-Bracero et al. (2003): EGS-Poster P0714. Rummel, U. et al. (2002): Eddy covariance measurements of nitric oxide flux within an Amazonian rain forest, Journal of Geophysical Research, 107

(D20), 8050, doi:10.1029/2001JD000520. Thielmann et al. (2003): EGS-AS16 oral presentation.