Abstract. 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 the In-service
Aircraft for a Global Observing System (IAGOS). Considering the high
interannual variability of biomass burning emissions and the episodic nature
of long-range pollution transport, one strength of this study is the amount
of data taken into account, namely 30 000 vertical profiles at nine clusters
of airports in Europe, North America, Asia, India and southern Africa over
the period 2002–2017. As a preliminary, a brief overview of the spatiotemporal 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). This study focuses on the free troposphere (altitudes above 2 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 110–150 (48) ppbv in Asia (Europe). Looking at the seasonal variation of
the frequency of occurrence, the 25 % strongest CO anomalies appear
reasonably well distributed throughout the year, in contrast to the 5 % or 1 %
strongest anomalies that exhibit a strong seasonality with, for instance, more
frequent anomalies during summertime in the 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 in Windhoek, Namibia. Depending on the location, these strong
anomalies are observed in different parts of the free troposphere. In order to investigate the role of biomass burning emissions in these
anomalies, we used the SOFT-IO (SOft attribution using FlexparT and carbon
monoxide emission inventories for In-situ Observation database) v1.0 IAGOS
added-value products that consist of FLEXible PARTicle dispersion model (FLEXPART) 20-day
backward simulations along all IAGOS aircraft trajectories, coupled with
anthropogenic Monitoring Atmospheric Composition and Climate (MACC)/CityZEN
EU projects (MACCity) and biomass burning Global Fire Assimilation System
(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 the summer
season. In both Japan and south India, the anthropogenic emissions dominate
all throughout 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. 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.
Tropospheric CO vertical profiles measured by IAGOS aircraft in
2002–2017 and the role of biomass burning
