Abstract
<p><strong>Abstract.</strong> This study investigates the role of biomass burning and long-range transport in the anomalies of carbon monoxide (CO) regularly observed along the tropospheric vertical profiles measured in the framework of IAGOS. Considering the high interannual variability of biomass burning emissions and the episodic nature of pollution long-range transport, one strength of this study is the amount of data taken into account, namely 30,000 vertical profiles at 9 clusters of airports in Europe, North America, Asia, India and southern Africa over the period 2002&amp;ndash;2017. </p> <p> As a preliminary, a brief overview of the spatio-temporal variability, latitudinal distribution, interannual variability and trends of biomass burning CO emissions from 14 regions is provided. The distribution of CO mixing ratios at different levels of the troposphere is also provided based on the entire IAGOS database (125 million CO observations). </p> <p> This study focuses on the free troposphere (altitudes above 2<span class="thinspace"></span>km) where the long-range transport of pollution is favoured. Anomalies at a given airport cluster are here defined as departures from the local seasonally-averaged climatological vertical profile. The intensity of these anomalies varies significantly depending on the airport, with maximum (minimum) CO anomalies of 110&amp;ndash;150 (48)<span class="thinspace"></span>ppbv in Asia (Europe). Looking at the seasonal variation of the frequency of occurrence, the 25<span class="thinspace"></span>% strongest CO anomalies appears reasonably well distributed along the year, in contrast to the 5<span class="thinspace"></span>% or 1<span class="thinspace"></span>% strongest anomalies that exhibit a strong seasonality with for instance more frequent anomalies during summertime in northern United-States, during winter/spring in Japan, during spring in South-east China, during the non-monsoon seasons in south-east Asia and south India, and during summer/fall at Windhoek, Namibia. Depending on the location, these strong anomalies are observed in different parts of the free troposphere. </p> <p> In order to investigate the role of biomass burning emissions in these anomalies, we used the SOFT-IO v1.0 IAGOS added-value products that consist of FLEXPART 20-days backward simulations along all IAGOS aircraft trajectories, coupled with anthropogenic (MACCity) and biomass burning (GFAS) CO emission inventories and vertical injections. SOFT-IO estimates the contribution (in ppbv) of the recent (less than 20 days) primary worldwide CO emissions, tagged per source region. Biomass burning emissions are found to play an important role in the strongest CO anomalies observed at most airport clusters. The regional tags indicate a large contribution from boreal regions at airport clusters in Europe and North America during summer season. In both Japan and south India, the anthropogenic emissions dominate all along the year, except for the strongest summertime anomalies observed in Japan that are due to Siberian fires. The strongest CO anomalies at airport clusters located in south-east Asia are induced by fires burning during spring in south-east Asia and during fall in equatorial Asia. In southern Africa, the Windhoek airport was mainly impacted by fires in southern hemisphere Africa and South America. </p> <p> To our knowledge, no other studies have used such a large dataset of in situ vertical profiles for deriving a climatology of the impact of biomass burning versus anthropogenic emissions on the strongest CO anomalies observed in the troposphere, in combination with information on the source regions. This study therefore provides both qualitative and quantitative information for interpreting the highly variable CO vertical distribution in several regions of interest.</p>
Highlights
In contrast with most anthropogenic emissions primarily confined to the planetary boundary layer (PBL), compounds emitted during open fires may be subject to pyroconvection, allowing a quick uplift in the free troposphere (Val Martin et al, 2010) and even the lower stratosphere under extreme conditions (Fromm et al, 2000, 2005; Fromm and Servranckx, 2003; Jost et al, 2004; Trentmann et al, 2006; Cammas et al, 2009)
Averaged over 2004–2012, the Microwave Limb Sounder (MLS) observations of carbon monoxide (CO) in the upper troposphere and lower stratosphere (UTLS) showed that trans-Pacific transport of CO from Asia to North America is strongest during spring and summer (Huang et al, 2016)
In the framework of In-service Aircraft for a Global Observing System (IAGOS), vertical profiles of tropospheric CO have been routinely measured at worldwide international airports since 2002
Summary
Biomass burning represents a major source of pollution throughout the troposphere, with strong impacts on the atmospheric composition (Duncan et al, 2003; Hodzic et al, 2007; Sauvage et al, 2007; Konovalov et al, 2011; Parrington et al, 2012; Yamasoe et al, 2015), air quality (Bravo et al, 2002; Sapkota et al, 2005; Bowman and Johnston, 2005; Viswanathan et al, 2006) and radiative balance (Forster et al, 2007; Spracklen et al, 2008; Stone et al, 2008; Péré et al, 2014). In contrast with most anthropogenic emissions primarily confined to the planetary boundary layer (PBL), compounds emitted during open fires may be subject to pyroconvection, allowing a quick uplift in the free troposphere (Val Martin et al, 2010) and even the lower stratosphere under extreme conditions (Fromm et al, 2000, 2005; Fromm and Servranckx, 2003; Jost et al, 2004; Trentmann et al, 2006; Cammas et al, 2009) At such altitudes, long-range transport is again favoured by stronger winds, sometimes allowing plumes to circumnavigate the world in 2–3 weeks (Damoah et al, 2004; Dirksen et al, 2009)
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