Greenhouse gas relationships in the Indian summer monsoon plume measured by the CARIBIC passenger aircraft

Abstract

Abstract. During the Indian summer monsoon period 2008, regular measurement flights were performed by the CARIBIC aircraft between Germany and India. Measurements included whole air sampling and subsequent analysis for greenhouse gases (CH 4 , CO 2 , N 2 O, SF 6 ) and in-situ measurements of CO, O 3 , and H 2 O. For all these tracers a distinct monsoon signature was observed in the longitude range 50-80 • E south of 40 • N at flight altitudes 8-12.5 km. The formation of a monsoon plume with enhanced mixing ratios was observed for CH 4 , N 2 O, SF 6 , CO and H 2 O. The plume began to develop in May and persisted through September, and maximum mixing ratios and maximum spatial extension of the plume were observed in August. For CO 2 and O 3 a minimum was observed. The amplitude of the CO 2 seasonal cycle was larger than at comparable latitudes outside the monsoon region, and the CO 2 spring maximum was observed with a delay of one month. Different tracer relationships show strong spatial variations across the plume. The comparison with NOAA ground station data shows a clear enhancement for CH 4 , N 2 O, SF 6 and CO and a decrease in CO 2 mixing ratios. Assuming seasonally invariant SF 6 emissions based on the EDGAR 4.0 inventory, monthly emissions were estimated for the period June-September for CH 4 , N 2 O, and CO, and the CO 2 uptake was estimated. While for N 2 O an emission decrease during the monsoon period was derived, emissions of CH 4 were highest in September indicating a different seasonal cycle of emissions. Net CO 2 uptake by the vegetation was largest in September.

The impact of the chemical production of methyl nitrate from the NO + CH<sub>3</sub>O<sub>2</sub> reaction on the global distributions of alkyl nitrates, nitrogen oxides and tropospheric ozone: a global modelling study

“…We use in situ measurements made from April until December 2008 made during flights from Frankfurt, Germany (50.0 • N, 8.5 • E) to Chennai, India (13.0 • N, 80.2 • E). The flights to and from Chennai take similar routes to those shown in Schuck et al (2010), providing a monthly snapshot of the distribution of NO y at the cruise altitude of 10-12 km throughout a large fraction of the year. The uncertainty associated with the CARIBIC NO y measurements is ∼ 8 % for mixing ratios around 450 ppt.…”

“…Examining the seasonal trend in the observations shows that between 15-25 • N there is a maximum in NO y mixing ratios towards the start of the year, which generally decreases by ∼ 30-50 % towards December. Previous studies have shown that emissions directly below the flight path have an impact on composition of the UT over India (Schuck et al, 2010). This reduction in NO y through the year may be partially explained by the occurrence of the Indian monsoon, where a larger fraction of NO y is lost via wet deposition, but also by the change in the location of the tropopause.…”

“…Williams et al, 2012). In this study the loss of CO at the surface by enzymatic processes in the soil (Yonemura et al, 2000) is parameterised with respect to the soil moisture content according to Sanderson et al (2003). The resistive fluxes are then passed into the dry deposition scheme of Ganzeveld and Lelieveld (1995).…”

Acetone variability in the upper troposphere: analysis of CARIBIC observations and LMDz-INCA chemistry-climate model simulations

“…Model and satellite data consistently localised high mixing ratios of CH 4 between 60 • E and 120 • E around 30 • N, a region included in our extended South Asian region (Table 2) at and above cruising altitude, at pressure altitudes between 300 and 100 hPa (Park et al, 2004;Xiong et al, 2009). Schuck et al (2010) showed that air masses sampled north of 30 • N generally travel for more than a week, in contrast with air masses south of 30 • N which had ground contact within the last four days prior to sampling. Baker et al (2011) confirmed that in the southern monsoon region, sampled air masses travelled 3 to 6 days before sampling, and 9 to 12 days in northern monsoon region.…”

Temporal variations of atmospheric CO<sub>2</sub> and CO at Ahmedabad in western India

“…Most of these measurements are made at weekly or fortnightly time intervals. Two aircraft-based measurement programmes, namely, Civil Aircraft for the regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) (Brenninkmeijer et al, 2007) and Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) (Machida et al, 2008) have provided an important first look at the southern Asian CO 2 budget, but these data have their own limitations (Patra et al, 2011;Schuck et al, 2010Schuck et al, , 2012. It is pertinent to mention here that until now, there have been no reports of CO 2 measurements over an urban location in India.…”