Upper-tropospheric CO and O<sub>3</sub> budget during the Asian summer monsoon

Abstract

Abstract. During the Asian summer monsoon, the circulation in the upper troposphere/lower stratosphere (UTLS) is dominated by the Asian monsoon anticyclone (AMA). Pollutants convectively uplifted to the upper troposphere are trapped within this anticyclonic circulation that extends from the Pacific Ocean to the Eastern Mediterranean basin. Among the uplifted pollutants are ozone (O 3 ) and its precursors, such as carbon monoxide (CO) and nitrogen oxides (NO x ). Many studies based on global modeling and satellite data have documented the source regions and transport pathways of primary pollutants (CO, HCN) into the AMA. Here, we aim to quantify the O 3 budget by taking into consideration anthropogenic and natural sources. We first use CO and O 3 data from the MetOp-A/IASI sensor to document their tropospheric distributions over Asia, taking advantage of the useful information they provide on the vertical dimension. These satellite data are used together with MOZAIC tropospheric profiles recorded in India to validate the distributions simulated by the global GEOS-Chem chemistry transport model. Over the Asian region, UTLS monthly CO and O 3 distributions from IASI and GEOS-Chem display the same large-scale features. UTLS CO columns from GEOS-Chem are in agreement with IASI, with a low bias of 11 ± 9 % and a correlation coefficient of 0.70. For O 3 , the model underestimates IASI UTLS columns over Asia by 14 ± 26 % but the correlation between both is high (0.94). GEOS-Chem is further used to quantify the CO and O 3 budget through sensitivity simulations. For CO, these simulations confirm that South Asian anthropogenic emissions have a more important impact on enhanced concentrations within the AMA (∼ 25 ppbv) than East Asian emissions (∼ 10 ppbv). The correlation between enhanced emissions over the Indo-Gangetic Plain and monsoon deep convection is responsible for this larger impact. Consistently, South Asian anthropogenic NO x emissions also play a larger role in producing O 3 within the AMA (∼ 8 ppbv) than East Asian emissions (∼ 5 ppbv), but Asian lightning-produced NO x is responsible for the largest O 3 production (10-14 ppbv). Stratosphere-to-troposphere exchanges are also important in transporting O 3 in the upper part of the AMA.

Dynamics and composition of the Asian summer monsoon anticyclone

“…Nevertheless our simulated net O 3 production rates in the ASMA (Fig. 7b) agree remarkably well with the independent estimate by Barret et al (2016).…”

“…We decided not to adapt the regions dynamically to the actual ASMA, because the boundary definitions we are aware of (Ploeger et al, 2015;Barret et al, 2016; emphasise the concept of a closed ASMA volume or transport barriers on monthly or seasonal timescales. However, the ASMA boundaries are not always well defined, particularly during transitions between different dynamical modes.…”

“…A mid-tropospheric (400-500 hPa) summertime O 3 maximum over the eastern Mediterranean/Middle Eastern region (Li et al, 2001;Lelieveld et al, 2009;Schuck et al, 2010;Akritidis et al, 2016) is enhanced by the Asian monsoon outflow (Y. Richards et al, 2013;Barret et al, 2016), but it is not clear whether O 3 in the ASMA plume is generally enhanced or depleted (Lawrence and Lelieveld, 2010).…”

A Portable Quantum Cascade Laser Spectrometer for Atmospheric Measurements of Carbon Monoxide

“…The red curve is the CO mean vertical profile obtained with the following procedure: we calculated the mean value of the CO mixing ratio for altitude intervals of 500 m; then we discarded the CO values which differ more than 90% from the mean value (in order to skip the CO anomalies); and finally we re-calculated the mean value in the altitude intervals. The CO vertical profiles shown in Figure 12 are consistent with CO data measured by other aircraft or satellite instruments [8,9,25,26]. …”

Climatology and long-term evolution of ozone and carbon monoxide in the UTLS at northern mid-latitudes, as seen by IAGOS from 1995 to 2013

“…In southern Asia, polluted surface air masses are uplifted by deep convection during the Asian Monsoon, up to the tropical UT. The western part of the anticyclonic circulation then transports poor-O 3 air masses northward and horizontally (Barret et al, 2016). This may impact the LS in MidE (Park et al, 2007), consistent with CH 4 measurements from IASI and AIRS and modelling with the CTM MOCAGE and the CCMs CNRM-AOCCM and LMDz-OR-INCA (Ricaud et al, 2014).…”