Tropospheric nitric oxide measurements over the Amazon Basin

Abstract

Horizontal and vertical distributions of nitric oxide (NO) were measured over the Amazon Basin during NASA's Global Tropospheric Experiment (GTE) Amazon Boundary Layer Experiment (ABLE 2A) mission in July-August 1985. During transit flights between the Virginia coast and Manaus, Brazil, NO mixing ratios were 12-15 parts per trillion by volume (pptv) at 5 km altitude. Values up to 200 pptv were observed in electrically active clouds. During longitudinal surveys over the Amazon region, NO mixing ratios in the lower planetary boundary layer decreased from 25-60 pptv over the central basin to 10-12 pptv in coastal regions. In the convective cloud layer or free troposphere, NO mixing ratios averaged 13 pptv in regions not influenced by biomass burning. No longitudinal trend above the mixed layer could be detected. A steep negative gradient with increasing altitude was noted within the mixed layer before midday. Mixing ratios decreased from 60 pptv at 0.2 km to about 15 pptv at the top of the mixed layer (1 km). No further change in mixing ratio with altitude through the convective cloud layer and lower edge of the free troposphere could be detected at this time. By midday, growth of the mixed layer height and enhanced mixing reduced the gradient, and evidence for mixing of NO into the convective cloud layer was noted. INTRODUCTION Tropical forests, soils, and wetland environments within the Amazon Basin ecosystem represent significant natural emission sources of many species important to atmospheric chemistry [Mayer et al., 1982; Crutzen and Gidel, 1983; Keller et al., 1986; Logan, 1983; Zimmerman et al., this issue; Kaplan et al., this issue; Bartlett et al., this issue; Rasmussen and Khalil, this issue]. In addition to natural sources, there are large anthropogenic emissions produced by biomass burning for agricultural purposes [Delany et al., 1985; Crutzen et al., 1985; Greenberg et al., 1984; Andreae et al., this issue]. The Amazon Boundary Layer Experiment (ABLE 2A) was an investigation of tropospheric chemistry over the Amazon Basin and of how this chemistry is affected by biosphere-atmosphere interactions [Harriss et al., this issue]. We present in this paper results of atmospheric nitric oxide (NO) measurements made during the ABLE 2A experiment. Intense solar flux and high concentrations of hydrocarbons and moisture in regions such as the Amazon Basin result in complex photochemical processes involving many species. These processes are often important sources or sinks for these species and, consequently, control their abundances and distributions [Logan et al., 1981; National Research Council, 1984]. This is especially true for ozone [Logan, 1985; Delany et al., 1985; Fishman et al., 1986, 1987; Jacob and Wofsy, this issue], one of the most important of the trace gases because of its role in hydroxyl radical production [Levy, 1972; 1973]. Photochemical production of ozone depends critically on the amount of nitric oxide that is present [Chameides, 1978; Fishman and Crutzen, 1978; Crutzen, 1979; Fishman et al.,

Ozone production and transport over the Amazon Basin during the dry-to-wet and wet-to-dry transition seasons

“…However, at night, dry deposition to the forest caused O 3 to drop below 5 ppb. Model results were consistent with the NO values of 25-60 ppt observed in the lower boundary layer over central Amazonia (Torres and Buchan, 1988). Isoprene emissions were found to have little effect on O 3 levels, as the oxidation of CO would produce sufficient hydrogen oxides (HO x ) to generate 20 ppb of O 3 .…”

“…13 and 15, respectively. Mean profiles from longitudinal surveys over Amazonia of O 3 during ABLE-2A and ABLE-2B (Harriss et al, 1990) and NO during ABLE-2A (Torres and Buchan, 1988) are included for comparison. In BARCA B, O 3 values were at or near background values in all regions, ranging from 8-15 ppb at the surface to 2-15 ppb at 4-4.5 km, and the models are generally within 5-10 ppb of the observations.…”

Impact of Manaus City on the Amazon Green Ocean atmosphere: ozone production, precursor sensitivity and aerosol load

“…Although the data base in tropical areas is still quite sparse, ground-based observations in the remote Amazon forest (not under the direct influence of biomass burning) appear to range from 20 to 100 ppt of NO. The somewhat higher NO x concentrations found in tropical forests, as compared to those observed in remote marine locations could result from the primary continental sources of biomass burning or from NO x emissions by soil (Kaplan et al, 1988;Torres and Buchan, 1988;Gut et al, 2002;Ganzeveld et al, 2002;Rummel et al, 2002). Alternatively they may derive from lightning activity within thunderstorms as observed over southern Brazil by Huntrieser et al (2007).…”

“…Singh et al (1990) reported a median NO concentration as low as 8 ppt at 0-6 km altitude over the Amazon basin in April-May 1987 (wet season), with little vertical gradient. Torres and Buchan (1988) observed boundary layer NO concentrations in the range 25-60 ppt over the central Amazon in July-August 1985. Although the data base in tropical areas is still quite sparse, ground-based observations in the remote Amazon forest (not under the direct influence of biomass burning) appear to range from 20 to 100 ppt of NO.…”

Biomass burning emissions disturbances on the isoprene oxidation in a tropical forest

“…During SAMBBA field experiment, in BG conditions (i.e., CO < 150 ppbv), the NOx mixing ratio ranged from 50 pptv to 200 pptv. Torres and Buchan (1988) (Table 3). This value of 40 ppbv at 600 m altitude is nearly two times the mean value of the O3 mixing ratio that we used as background in the enhancement ratio, and even out of the range of the standard deviation (21 ppbv, SD=7).…”