Long-term trends of black carbon and particle number concentration in the lower free troposphere in Central Europe

Abstract Background The implementation of emission mitigation policies in Europe over the last two decades has generally improved the air quality, which resulted in lower aerosol particle mass, particle number, and black carbon mass concentration. However, little is known whether the decreasing particle concentrations at a lower-altitude level can be observed in the free troposphere (FT), an important layer of the atmosphere, where aerosol particles have a longer lifetime and may affect climate dynamics. In this study, we used data from two high-Alpine observatories, Zugspitze-Schneefernerhaus (ZSF) and Jungfraujoch (JFJ), to assess the long-term trends on size-resolved particle number concentrations (PNCs) and equivalent black carbon (eBC) mass concentration separated for undisturbed lower FT conditions and under the influence of air from the planetary boundary layer (PBL) from 2009 to 2018. Results The FT and PBL-influenced conditions were segregated for both sites. We found that the FT conditions in cold months were more prevalent than in warm months, while the measured aerosol parameters showed different seasonal patterns for the FT and PBL-influenced conditions. The pollutants in the PBL-influenced condition have a higher chance to be transported to high-altitudes due to the mountainous topography, leading to a higher concentration and more distinct seasonal variation, and vice versa. The long-term trends of the measured aerosol parameters were evaluated and the decreased aerosol concentrations were observed for both FT and PBL-influenced conditions. The observed decreasing trends in eBC concentration in the PBL-influenced condition are well consistent with the reported trends in total BC emission in Germany and Switzerland. The decreased concentrations in the FT condition suggest that the background aerosol concentration in the lower FT over Central Europe has correspondingly decreased. The change of back trajectories in the FT condition at ZSF and JFJ was further evaluated to investigate the other possible drivers for the decreasing trends. Conclusions The background aerosol concentration in the lower FT over Central Europe has significantly decreased during 2009–2018. The implementation of emission mitigation policies is the most decisive factor and the decrease of the regional airmass occurrence over Central Europe also has contributed to the decreasing trends.

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Decreasing trends of particle number and black carbon mass concentrations at 16 observational sites in Germany from 2009 to 2018

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-7049-2020 ◽

2020 ◽

Vol 20 (11) ◽

pp. 7049-7068 ◽

Cited By ~ 6

Author(s):

Jia Sun ◽

Wolfram Birmili ◽

Markus Hermann ◽

Thomas Tuch ◽

Kay Weinhold ◽

...

Keyword(s):

Black Carbon ◽

Mass Concentration ◽

Particle Number ◽

Spatial Scales ◽

Road Transport ◽

Anthropogenic Emissions ◽

Emission Mitigation ◽

Atmospheric Particle ◽

Mitigation Policies

Abstract. Anthropogenic emissions are dominant contributors to air pollution. Consequently, mitigation policies have been attempted since the 1990s in Europe to reduce pollution by anthropogenic emissions. To evaluate the effectiveness of these mitigation policies, the German Ultrafine Aerosol Network (GUAN) was established in 2008, focusing on black carbon (BC) and sub-micrometre aerosol particles. In this study, long-term trends of atmospheric particle number concentrations (PNCs) and equivalent BC (eBC) mass concentration over a 10-year period (2009–2018) were determined for 16 GUAN sites ranging from roadside to high Alpine environments. Overall, statistically significant decreasing trends are found for most of these parameters and environments in Germany. The annual relative slope of eBC mass concentration varies between −13.1 % and −1.7 % per year. The slopes of the PNCs vary from −17.2 % to −1.7 %, −7.8 % to −1.1 %, and −11.1 % to −1.2 % per year for 10–30, 30–200, and 200–800 nm size ranges, respectively. The reductions in various anthropogenic emissions are found to be the dominant factors responsible for the decreasing trends of eBC mass concentration and PNCs. The diurnal and seasonal variations in the trends clearly show the effects of the mitigation policies for road transport and residential emissions. The influences of other factors such as air masses, precipitation, and temperature were also examined and found to be less important or negligible. This study proves that a combination of emission mitigation policies can effectively improve the air quality on large spatial scales. It also suggests that a long-term aerosol measurement network at multi-type sites is an efficient and necessary tool for evaluating emission mitigation policies.

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Decreasing Trends of Particle Number and Black Carbon Mass Concentrations at 16 Observational Sites in Germany from 2009 to 2018

10.5194/acp-2019-754 ◽

2019 ◽

Author(s):

Jia Sun ◽

Wolfram Birmili ◽

Markus Hermann ◽

Thomas Tuch ◽

Kay Weinhold ◽

...

Keyword(s):

Time Series ◽

Black Carbon ◽

Urban Areas ◽

Mass Concentration ◽

Particle Number ◽

Regional Scale ◽

Particle Diameter ◽

Anthropogenic Emissions ◽

Mitigation Policies ◽

Mass Concentrations

Abstract. Anthropogenic emissions are a dominant contributor to air pollution. Consequently, mitigation policies have attempted to reduce anthropogenic pollution emissions in Europe since the 1990s. To evaluate the effectiveness of these mitigation policies, the German Ultrafine Aerosol Network (GUAN) was established in 2008, focusing on black carbon and sub-micrometer aerosol particles, especially ultrafine particles. In this investigation, trends of the size-resolved particle number concentrations (PNC) and the equivalent black carbon (eBC) mass concentration over a 10-year period (2009–2018) were evaluated for 16 observational sites for different environments among GUAN. The trend analysis was done for both, the full-length time series and on subsets of the time series in order to test the reliability of the results. The results show generally decreasing trends of both, the PNCs for all size ranges as well as eBC mass concentrations in all environments, except PNC in 10–30 nm at regional background and mountain sites. The annual slope of the eBC mass concentration varies between −7.7 % and −1.8 % per year. The slopes of the PNCs varies from −6.3 % to 2.7 %, −7.0 % to −2.0 %, and −9.5 % to −1.5 % per year (only significant trends) for 10–30 nm, 30–200 nm, and 200–800 nm particle diameter, respectively. The regional Mann-Kendall test yielded regional-scale trends of eBC mass concentration, N[30–200] and N[200–800] of −3.8 %, −2.0 % and −2.4 %, respectively, indicating an overall decreasing trend for eBC mass concentration and sub-micrometer PNC (except N[10–30]) all over Germany. The most significant decrease was observed on working days and during daytime in urban areas, which implies a strong evidence of reduced anthropogenic emissions. For the seasonal trends, stronger reductions were observed in winter. Possible reasons for this reduction can be the increased average ambient temperatures and wind speed in winter, which resulted in less domestic heating and stronger dilution. In addition, decreased precipitation in summer also diminishes the decrease of the PNCs and eBC mass concentration. For the period of interest, there were no significant changes in long-range transport patterns. The most likely factors for the observed decreasing trends are declining anthropogenic emissions due to emission mitigation policies of the European Union.

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Long-term trends of MLT region winds over Central Europe

Physics and Chemistry of the Earth Parts A/B/C ◽

10.1016/j.pce.2005.01.004 ◽

2006 ◽

Vol 31 (1-3) ◽

pp. 16-21 ◽

Cited By ~ 10

Author(s):

Ch. Jacobi ◽

D. Kürschner

Keyword(s):

Central Europe ◽

Long Term Trends ◽

Mlt Region

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Long-term trends of black carbon and sulphate aerosol in the Arctic: changes in atmospheric transport and source region emissions

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-12133-2010 ◽

2010 ◽

Vol 10 (5) ◽

pp. 12133-12184 ◽

Cited By ~ 2

Author(s):

D. Hirdman ◽

J. F. Burkhart ◽

H. Sodemann ◽

S. Eckhardt ◽

A. Jefferson ◽

...

Keyword(s):

Black Carbon ◽

Atmospheric Circulation ◽

Atmospheric Transport ◽

Particle Dispersion ◽

Downward Trend ◽

The Arctic ◽

Northern Eurasia ◽

Source Regions ◽

Long Term Trends

Abstract. As a part of the IPY project POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols and Transport) and building on previous work (Hirdman et al., 2010), this paper studies the long-term trends of both atmospheric transport as well as equivalent black carbon (EBC) and sulphate for the three Arctic stations Alert, Barrow and Zeppelin. We find a general downward trend in the measured EBC concentrations at all three stations, with a decrease of −2.1±0.4 ng m−3 yr−1 (for the years 1989–2008) and −1.4±0.8 ng m−3 yr−1 (2002–2009) at Alert and Zeppelin respectively. The decrease at Barrow is, however, not statistically significant. The measured sulphate concentrations show a decreasing trend at Alert and Zeppelin of −15±3 ng m−3 yr−1 (1985–2006) and −1.3±1.2 ng m−3 yr−1 (1990–2008) respectively, while the trend at Barrow is unclear. To reveal the influence of different source regions on these trends, we used a cluster analysis of the output of the Lagrangian particle dispersion model FLEXPART run backward in time from the measurement stations. We have investigated to what extent variations in the atmospheric circulation, expressed as variations in the frequencies of the transport from four source regions with different emission rates, can explain the long-term trends in EBC and sulphate measured at these stations. We find that the long-term trend in the atmospheric circulation can only explain a minor fraction of the overall downward trend seen in the measurements of EBC (0.3–7.2%) and sulphate (0.3–5.3%) at the Arctic stations. The changes in emissions are dominant in explaining the trends. We find that the highest EBC and sulphate concentrations are associated with transport from Northern Eurasia and decreasing emissions in this region drive the downward trends. Northern Eurasia (cluster: NE, WNE and ENE) is the dominant emission source at all Arctic stations for both EBC and sulphate during most seasons. In wintertime, there are indications that the EBC emissions from the eastern parts of Northern Eurasia (ENE cluster) have increased over the last decade.

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Long-Term Trends in Marine Boundary Layer Properties over the Atlantic Ocean

Journal of Climate ◽

10.1175/jcli-d-18-0219.1 ◽

2019 ◽

Vol 32 (10) ◽

pp. 2991-3004 ◽

Cited By ~ 1

Author(s):

Juan P. Díaz ◽

Francisco J. Expósito ◽

Juan C. Pérez ◽

Albano González ◽

Yuqing Wang ◽

...

Keyword(s):

Boundary Layer ◽

Atlantic Ocean ◽

Marine Boundary Layer ◽

Inversion Layer ◽

Precipitable Water ◽

Cloud Formation ◽

Climate Projections ◽

Free Troposphere ◽

Long Term Trends

Abstract The marine boundary layer (MBL) is a key component of Earth’s climate system, and its main characteristics (height, entrainment efficiency, energy and mass fluxes, cloud formation processes, etc.) are closely linked to the properties of the inversion layer, which generally determines its height. Furthermore, cloud response to a warmer climate, one of the main sources of uncertainty in future climate projections, is highly dependent on changes in the MBL and in the inversion-layer properties. Long-term trends of the time series of MBL parameters at 32 stations in the Atlantic Ocean have been analyzed using conveniently homogenized radiosonde profiles from 1981 to 2010. In general, decreasing trends are found in the strength and thickness of the inversion layer and in the difference between the precipitable water vapor (PWV) in the free troposphere and the MBL. In contrast, positive trends are found in the height of the bottom of the inversion layer, the lapse rates of virtual and equivalent potential temperatures, the PWV within the boundary layer, and the sea surface temperature (SST). The weakening trend of the inversion layer and the increasing desiccation of the free troposphere relative to the MBL could have important consequences for both the evolution of low cloud cover in a greenhouse-warming climate and the fragile local ecosystems, such as “cloud forests.”

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