Global Atmosphere Watch Station Research Articles

Atmospheric black carbon in the metropolitan area of La Paz and El Alto, Bolivia: concentration levels and emission sources

Abstract. Black carbon (BC) is a major component of submicron particulate matter (PM), with significant health and climate impacts. Many cities in emerging countries lack comprehensive knowledge about BC emissions and exposure levels. This study investigates BC concentration levels, identifies its emission sources, and characterizes the optical properties of BC at urban background sites of the two largest high-altitude Bolivian cities: La Paz (LP) (3600 m above sea level) and El Alto (EA) (4050 m a.s.l.), where atmospheric oxygen levels and intense radiation may affect BC production. The study relies on concurrent measurements of equivalent black carbon (eBC), elemental carbon (EC), and refractory black carbon (rBC) and their comparison with analogous data collected at the nearby Chacaltaya Global Atmosphere Watch Station (5240 m a.s.l). The performance of two independent source apportionment techniques was compared: a bilinear model and a least-squares multilinear regression (MLR). Maximum eBC concentrations were observed during the local dry season (LP: eBC = 1.5 ± 1.6 µg m−3; EA: 1.9±2.0 µg m−3). While eBC concentrations are lower at the mountain station, daily transport from urban areas is evident. Average mass absorption cross sections of 6.6–8.2 m2 g−1 were found in the urban area at 637 nm. Both source apportionment methods exhibited a reasonable level of agreement in the contribution of biomass burning (BB) to absorption. The MLR method allowed the estimation of the contribution and the source-specific optical properties for multiple sources, including open waste burning.

Multiparameter Detection of Summer Open Fire Emissions: The Case Study of GAW Regional Observatory of Lamezia Terme (Southern Italy)

In Southern Mediterranean regions, the issue of summer fires related to agriculture practices is a periodic recurrence. It implies a significant increase in carbon dioxide (CO2) emissions and other combustion-related gaseous and particles compounds emitted into the atmosphere with potential impacts on air quality and global climate. In this work, we performed an analysis of summer fire events that occurred on August 2021. Measurements were carried out at the permanent World Meteorological Organization (WMO)/Global Atmosphere Watch (GAW) station of Lamezia Terme (Code: LMT) in Calabria, Southern Italy. The observatory is equipped with greenhouse gases and black carbon analyzers, an atmospheric particulate impactor system, and a meteo-station for atmospheric parameters to characterize atmospheric mechanisms and transport for land and sea breezes occurrences. High mole fractions of carbon monoxide (CO) and carbon dioxide (CO2) coming from quadrants of inland areas were correlated with fire counts detected via the MODIS satellite (GFED-Global Fire Emissions Database) at 1 km of spatial resolution. In comparison with the typical summer values, higher CO and CO2 were observed in August 2021. Furthermore, the growth in CO concentration values in the tropospheric column was also highlighted by the analyses of the L2 products of the Copernicus SP5 satellite. Wind fields were reconstructed via a Weather Research and Forecasting (WRF) output, the latter suggesting a possible contribution from open fire events observed at the inland region near the observatory. So far, there have been no documented estimates of the effect of prescribed burning on carbon emissions in this region. This study suggested that data collected at the LMT station can be useful in recognizing and consequently quantifying emission sources related to open fires.

A quality-assured dataset of nine radiation components observed at the Shangdianzi regional GAW station in China (2013–2022)

Abstract. The New Baseline Surface Radiation (NBSR) system was established at the Shangdianzi (SDZ) regional Global Atmosphere Watch (GAW) station in 2013 to observe nine broadband radiation components, i.e. the global, direct, diffuse, and upwelling shortwave irradiance (GSWI, DSWI, DifSWI, and UpSWI); the photosynthetically active radiation (PAR); the ultraviolet irradiance (UVAI and UVBI); and the down- and upwelling longwave irradiance (DnLWI and UpLWI). To test the 1 min raw radiometric data, a Hybrid Algorithm for Radiation Data Quality Control (HARDQC) is presented in this study based on well-established methods, together with the solar irradiance dataset and the spectral features of the instrument bands. Subsequently, a NBSR dataset, which consists of radiation data at multiple timescales (i.e. 1 min, hourly, daily, monthly, monthly average hourly, and monthly average daily) over 2013–2022, is established and evaluated. Results show that more than 98.7 % of all radiation components passed the physical possibility test. The percentages of those that passed the extremely rare test are greater than 98.6 % for all radiation components except for the DnLWI (97.1 %). The percentages of those that passed the comparison test are greater than 83.3 % (GSWI), 78.3 % (DSWI), 81.7 % (DifSWI), 93.1 % (UpSWI), 88.9 % (PAR), 95.6 % (UVAI), 96.3 % (UVBI), 99.8 % (DnLWI), and 99.7 % (UpLWI), respectively. Due to data logger faults, removal of the instruments for calibration, and lightning strikes, some apparent data gaps in the upwelling radiation components (January 2015–August 2017) and all radiation components (December 2018; July to September 2021) were detected. Despite the existence of a few imperfections in the NBSR dataset, it is still reliable to apply it in many fields such as the validation of satellite products and numerical models, the investigation of relationships between radiation and atmospheric composition, and the detection of changes in the surface fluxes. The dataset described in this paper is available at https://doi.org/10.1594/PANGAEA.963330 (Quan et al., 2023b).

Investigating the differences in calculating global mean surface CO2 abundance: the impact of analysis methodologies and site selection

Abstract. The World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) coordinates high-quality atmospheric greenhouse gas observations globally and provides these observations through the WMO World Data Centre for Greenhouse Gases (WDCGG) supported by Japan Meteorological Agency. The WDCGG and the National Oceanic and Atmospheric Administration (NOAA) analyse these measurements using different methodologies and site selection to calculate global annual mean surface CO2 and its growth rate as a headline climate indicator. This study introduces a third hybrid method named GFIT, which serves as an independent validation and open-source alternative to the methods described by NOAA and WDCGG. We apply GFIT to incorporate observations from most WMO GAW stations and 3D modelled CO2 fields from CarbonTracker Europe (CTE). We find that different observational networks (i.e. NOAA, GAW, and CTE networks) and analysis methods result in differences in the calculated global surface CO2 mole fractions equivalent to the current atmospheric growth rate over a 3-month period. However, the CO2 growth rate derived from these networks and the CTE model output shows good agreement. Over the long-term period (40 years), both networks with and without continental sites exhibit the same trend in the growth rate (0.030 ± 0.002 ppm yr−1 each year). However, a clear difference emerges in the short-term (1-month) change in the growth rate. The network that includes continental sites improves the early detection of changes in biogenic emissions.

Sources and long-term variability of carbon monoxide at Mount Kenya and in Nairobi

Abstract. Carbon monoxide (CO) concentrations in the troposphere are decreasing globally, with Africa as an exception. Yet, the region is understudied, with a deficit of ground-based observations and highly uncertain CO emission inventories. This paper reports multiyear observational CO data from the Mt. Kenya Global Atmosphere Watch (GAW) station, as well as summertime CO isotope observations from both Mt. Kenya and Nairobi, Kenya. The CO variability at Mt. Kenya is characterized by slightly increased concentrations during dry periods and a strong influence of short-term pollution events. While some data gaps and differences in instrumentation complicate decadal-scale trend analysis, a small long-term increase is resolved. High-pollution events are consistent with isotopic signal from downwind savanna fires. The isotope fingerprint of CO in Nairobi indicates an overwhelming dominance (near 100 %) of primary emissions from fossil fuel combustion with implications for air pollution policy. In contrast, the isotope signature of CO intercepted at the large-footprint Mt. Kenya region suggests that at least 70 % is primary sourced, with a predominance likely from savanna fires in Africa. Taken together, this study provides quantitative constraints of primary vs. secondary CO in the eastern Africa region and in urban Nairobi, with implications for satellite-based emission inventories as well as for chemical transport and climate modeling.

Local comparisons of tropospheric ozone: vertical soundings at two neighbouring stations in southern Bavaria

Abstract. In this study ozone profiles of the differential-absorption lidar at Garmisch-Partenkirchen are compared with those of ozone sondes of the Forschungszentrum Jülich and of the Meteorological Observatory Hohenpeißenberg (German Weather Service). The lidar measurements are quality assured by the highly accurate nearby in situ ozone measurements at the Wank (1780 m a.s.l.) and Zugspitze (2962 m a.s.l.) summits and at the Global Atmosphere Watch station Schneefernerhaus (UFS, 2670 m a.s.l.), at distances of 9 km or less from the lidar. The mixing ratios of the lidar agree with those of the monitoring stations, with a standard deviation (SD) of 1.5 ppb, and feature a slight positive offset of 0.6 ± 0.6 ppb (SD) conforming to the known −1.8 % calibration bias of the in situ instruments. Side-by-side soundings of the lidar and electrochemical (ECC) sonde measurements in February 2019 by a team of the Forschungszentrum Jülich shows small positive ozone offsets for the sonde with respect to the lidar and the mountain stations (0.5 to 3.4 ppb). After applying an altitude-independent bias correction to the sonde data an agreement to within just ±2.5 ppb in the troposphere was found, which we regard as the wintertime uncertainty of the lidar. We conclude that the recently published uncertainties of the lidar in the final configuration since 2012 are realistic and rather small for low to moderate ozone concentrations. Comparisons of the lidar with the Hohenpeißenberg routine measurements with Brewer-Mast sondes are more demanding because of the distance of 38 km between the two sites implying significant ozone differences in some layers, particularly in summer. Our comparisons cover the 3 years September 2000 to August 2001, 2009, and 2018. A slight negative average offset (−3.64 ± 3.72 ppb (SD)) of the sondes with respect to the lidar was found. We conclude that most Hohenpeißenberg sonde data could be improved in the troposphere by recalibration with the Zugspitze station data (1978 to 2011 summit, afterwards UFS). This would not only remove the average offset but also greatly reduce the variability of the individual offsets. The comparison for 2009 suggests a careful partial re-evaluation of the lidar measurements between 2007 and 2011 for altitudes above 6 km, where occasionally a negative bias occurred.

On the Large Variation in Atmospheric CO2 Concentration at Shangdianzi GAW Station during Two Dust Storm Events in March 2021

Dust storms have large impacts on air quality and meteorological elements; however, their relationships with atmospheric greenhouse gases (e.g., CO2) and radiation components remain uncertain. In this study, the co-variation of dust and CO2 concentrations and its possible influencing mechanism are examined using observations at the Shangdianzi (SDZ) regional Global Atmosphere Watch (GAW) station along with simulations of the Vegetation Photosynthesis and Respiration Model coupled with the Weather Research and Forecasting model (WRF-VPRM), during two dust storm events on 15 and 28 March 2021. During these events, hourly CO2 concentrations decreased by 40–50 ppm at SDZ while dust concentrations increased to 1240.6 and 712.4 µg m−3. The elevated dust increased diffusive shortwave irradiance by 50–60% and decreased direct shortwave irradiance by ~60% along with clouds. The dust events were attributed to the passages of two cold front systems over northern China. At SDZ, during the frontal passages, wind speed increased by 3–6 m s−1, and relative humidity decreased by 50–60%. The CO2 variations associated with the frontal systems were captured by the WRF-VPRM despite the overestimated surface CO2 level at SDZ. Biogenic CO2 flux plays an indistinctive role in the large CO2 variation at SDZ, as it is weak during the non-growing season. The cold fronts pushed polluted air southeastward over the North China Plain and replaced it with low-CO2 air from Northwest China, leading to the decline in CO2. These findings demonstrate that mesoscale synoptic conditions significantly affect the regional transport and dispersion of CO2, which can influence the prediction of terrestrial carbon balance on a regional scale.

Measurement report: Long-range transport and the fate of dimethyl sulfide oxidation products in the free troposphere derived from observations at the high-altitude research station Chacaltaya (5240 m a.s.l.) in the Bolivian Andes

Abstract. Dimethyl sulfide (DMS) is the primary natural contributor to the atmospheric sulfur burden. Observations concerning the fate of DMS oxidation products after long-range transport in the remote free troposphere are, however, sparse. Here we present quantitative chemical ionization mass spectrometric measurements of DMS and its oxidation products sulfuric acid (H2SO4), methanesulfonic acid (MSA), dimethylsulfoxide (DMSO), dimethylsulfone (DMSO2), methanesulfinic acid (MSIA), methyl thioformate (MTF), methanesulfenic acid (MSEA, CH3SOH), and a compound of the likely structure CH3S(O)2OOH in the gas phase, as well as measurements of the sulfate and methanesulfonate aerosol mass fractions. The measurements were performed at the Global Atmosphere Watch (GAW) station Chacaltaya in the Bolivian Andes located at 5240 m above sea level (a.s.l.). DMS and DMS oxidation products are brought to the Andean high-altitude station by Pacific air masses during the dry season after convective lifting over the remote Pacific ocean to 6000–8000 m a.s.l. and subsequent long-range transport in the free troposphere (FT). Most of the DMS reaching the station is already converted to the rather unreactive sulfur reservoirs DMSO2 in the gas phase and methanesulfonate (MS−) in the particle phase, which carried nearly equal amounts of sulfur to the station. The particulate sulfate at Chacaltaya is however dominated by regional volcanic emissions during the time of the measurement and not significantly affected by the marine air masses. In one of the FT events, even some DMS was observed next to reactive intermediates such as methyl thioformate, dimethylsulfoxide, and methanesulfinic acid. Also for this event, back trajectory calculations show that the air masses came from above the ocean (distance >330 km) with no local surface contacts. This study demonstrates the potential impact of marine DMS emissions on the availability of sulfur-containing vapors in the remote free troposphere far away from the ocean.

Wet season chemical composition of atmospheric wet deposition at Cape Point

The measurement of precipitation chemistry enables the assessment of the temporal and spatial evolution of the chemical composition of the atmosphere associated with atmospheric physical and chemical mechanisms. The aims of this study were to report the chemical composition of rainwater collected at a marine environment, i.e. the Cape Point Global Atmosphere Watch (CPT GAW) station from 2004 to 2012. As expected, the volume weighted mean (VWM) concentrations of Na+ (298.64 μEq.L-1) and Cl- (354.18 μEq.L-1) were significantly higher compared to the VWM concentrations of other ionic species, as well as compared to the VWM concentrations thereof at the sites in the South African interior. The average pH of rainwater was slightly lower than the pH of unpolluted rainwater, mainly due to NO3- associated with the occasional influence of the Cape Town metropole. In contrast to the sites situated in the north-eastern South African interior, where anthropogenic SO42- was the major constituent in rainwater, SO42- at CPT GAW was entirely associated with marine air with no anthropogenic contribution. It was also indicated that 94% of the chemical content at CPT GAW can be attributed to the marine source.

Background levels of black carbon over remote marine locations

Approximately 80% of the Southern Hemisphere (SH) surface is oceanic, while the Northern Hemisphere (NH) hosts 85% of the world's population along with a broadly equivalent anthropogenic emissions contribution. Consequently, the so-called ‘background’ marine air loading would be expected to be notably lower, or cleaner, in the SH than that over the NH. To test this supposition, we investigate the levels of air pollution over the Northeast Atlantic, at the Mace Head Global Atmospheric Watch station (located 53.3253°N, 9.9044°W), and on a ship-borne cruise in the Southern Ocean (50–65°S and 40–65°W). The highly sensitive single-particle soot photometer (SP2) was deployed to measure refractory black carbon (BC) at one-minute temporal resolution during the Austral Summer from January 2nd – February 12th 2015 for the SH campaign and April 2nd – 20th 2015 for the NH campaign. The aerosol organic matter (OM) was also measured as a relevant adjunct measurement. We found the percentage ‘frequency-of-occurrence’ of BC mass concentration ranging from 0 to 1000 ng m−3. For both the SH and NH distributions, we found that these distributions could be fitted by a series of lognormal distributions (8-modes). The SH distribution had four modes with BC concentrations <0.1 ng m−3, while the NH distribution had only one mode at concentrations <0.1 ng m−3. Both distributions had a maximum modal occurrence of ~270 ng m−3. The lognormal distributions are statistical representations of particular aerosol sources or ageing. In this context, we can regard the lower concentration modes in the frequency-of-occurrence distribution as representative of the marine background. Consequently, we conclude, using BC as an anthropogenic tracer, that while both oceans show low background concentrations of refractory BC, the SH campaign was cleaner much more frequently. The addition of regression and correlation analysis of OM vs BC also define what levels of BC can be regarded as thresholds for distinguishing between natural and anthropogenic OM over oceans, particularly in the NH where biogenic OM may be significantly greater than in the SH.

Hydrochemistry of atmospheric precipitation over an urban station in the peninsular India: Assessment of the long-term data

Long-term data on precipitation chemistry is crucial for the formulation of climatology of major acidifying as well as neutralizing components and their trends over the years. Rain water samples were collected during the monsoon season (June to September) for three decades (1981–2016) at Pune, an urban global atmospheric watch (GAW) station in the peninsular India. The long-term volume weighted mean (VWM) pH was 5.91 ± 0.57. The pH showed a significantly decreasing trend with about 9% acidic occurrences. Temporal variation of annual mean nss SO42- and NO3-showed an increasing trend whereas, a decreasing trend of NH4+and an increasing trend of Ca 2+was observed. The lowest mean wet deposition flux during the monsoon season over the entire period was observed for NH4+and highest was for NO3-. Source apportionment for ionic components through Positive Matrix Factorization (PMF) indicated the factor comprising of crustal source contributed 35% to the total ionic concentration followed by the sea salt ions that comprised of 33%. The anthropogenic sources mainly comprising of industrial, vehicular, agricultural and residential activities also contributed significantly (25%) indicating the importance of man-made emissions in driving the rain water composition and the associated pH around the region.

The SALTENA Experiment: Comprehensive Observations of Aerosol Sources, Formation, and Processes in the South American Andes

Abstract This paper presents an introduction to the Southern Hemisphere High Altitude Experiment on Particle Nucleation and Growth (SALTENA). This field campaign took place between December 2017 and June 2018 (wet to dry season) at Chacaltaya (CHC), a GAW (Global Atmosphere Watch) station located at 5,240 m MSL in the Bolivian Andes. Concurrent measurements were conducted at two additional sites in El Alto (4,000 m MSL) and La Paz (3,600 m MSL). The overall goal of the campaign was to identify the sources, understand the formation mechanisms and transport, and characterize the properties of aerosol at these stations. State-of-the-art instruments were brought to the station complementing the ongoing permanent GAW measurements, to allow a comprehensive description of the chemical species of anthropogenic and biogenic origin impacting the station and contributing to new particle formation. In this overview we first provide an assessment of the complex meteorology, airmass origin, and boundary layer–free troposphere interactions during the campaign using a 6-month high-resolution Weather Research and Forecasting (WRF) simulation coupled with Flexible Particle dispersion model (FLEXPART). We then show some of the research highlights from the campaign, including (i) chemical transformation processes of anthropogenic pollution while the air masses are transported to the CHC station from the metropolitan area of La Paz–El Alto, (ii) volcanic emissions as an important source of atmospheric sulfur compounds in the region, (iii) the characterization of the compounds involved in new particle formation, and (iv) the identification of long-range-transported compounds from the Pacific or the Amazon basin. We conclude the article with a presentation of future research foci. The SALTENA dataset highlights the importance of comprehensive observations in strategic high-altitude locations, especially the undersampled Southern Hemisphere.

Measurement report: Long-term variations in surface NO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; and SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; mixing ratios from 2006 to 2016 at a background site in the Yangtze River Delta region, China

Abstract. China has been experiencing rapid changes in emissions of air pollutants in recent decades. Increased emissions of primary particulates and reactive gases caused severe haze in several polluted regions including the Yangtze River Delta (YRD). Measures implemented in recent years for improving air quality have reduced the emissions of NOx, SO2, etc. The emission changes in these gases are reflected by tropospheric columns from satellite observations and surface measurements of surface concentrations from urban sites. However, little is known about the long-term variations in regional background NOx and SO2. In this study, we present NOx and SO2 measurements from the Lin'an station (LAN; 30∘18' N, 119∘44′ E; 138.6 m a.s.l.), one of the Global Atmosphere Watch (GAW) stations in China. We characterize the seasonal and diurnal variations and study the long-term trends of NOx and SO2 mixing ratios observed at LAN from 2006 to 2016. We also interpret the observed variations and trends in terms of changes in meteorological conditions as well as emission of these gases. The overall average mixing ratios of NOx (NO2) and SO2 during 2006–2016 were 13.6 ± 1.2 ppb (12.5 ± 4.6) and 7.0 ± 4.2 ppb, respectively. The averaged seasonal variations showed maximum values of NOx and SO2 in December (23.5 ± 4.4 ppb) and January (11.9 ± 6.2 ppb), respectively, and minimum values of 7.1 ± 0.8 and 2.8 ± 2.3 ppb (both in July), respectively. The average diurnal variation characteristics of NOx and SO2 differed considerably from each other, though the daily average mixing ratios of both gases were significantly correlated (R2=0.29, P&lt;0.001). The annual average mixing ratio of NOx increased during 2006–2011 and then decreased significantly at 0.78 ppb/yr (−5.16 %/yr, P&lt;0.01). The annual 95th and 5th percentiles of hourly NOx mixing ratios showed upward trends until 2012 and 2014, respectively, before a clear decline. The annual average mixing ratio of SO2 decreased significantly at 0.99 ppb/yr (−8.27 %/yr, P&lt;0.01) from 2006–2016. The annual 95th and 5th percentiles of hourly SO2 mixing ratios all exhibited significant (P&lt;0.001) downward trends at 3.18 and 0.19 ppb/yr, respectively. Changes in the total NOx and SO2 emissions as well as the industrial emissions in the YRD region were significantly correlated with the changes in annual NOx and SO2 mixing ratios. The significant decreases in NOx from 2011 to 2016 and SO2 from 2006 to 2016 highlight the effectiveness of relevant control measures on the reduction in NOx and SO2 emissions in the YRD region. A decrease in annual SO2 / NOx ratio was found, suggesting a better efficacy in the emission reduction in SO2 than NOx. We found gradual changes in average diurnal patterns of NOx and SO2, which could be attributed to increasing contributions of vehicle emissions to NOx and weakening impacts of large sources on the SO2 concentration. This study reaffirms China's success in controlling both NOx and SO2 in the YRD but indicates at the same time a necessity to strengthen the NOx emission control.

Speciated atmospheric mercury at the Waliguan Global Atmosphere Watch station in the northeastern Tibetan Plateau: implication of dust-related sources for particulate bound mercury

Abstract. To understand the ambient levels and sources of atmospheric mercury (Hg) in the Tibetan Plateau, a full-year continuous measurement of speciated atmospheric mercury was conducted at the Waliguan (WLG) Baseline Observatory (3816 m a.s.l.) from May 2012 to April 2013. Mean concentrations (± 1 SD) of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particulate bound mercury (PBM) during the whole study period were 1.90±0.80 ng m−3, 12.0±10.6 and 65.4±63.2 pg m−3, respectively. Seasonal variations of GEM were very small, while those of PBM were quite large with mean values being 4 times higher in the cold (102.3±66.7 pg m−3) than warm (22.8±14.6 pg m−3) season. Anthropogenic emissions to the east of the Tibetan Plateau contributed significantly to GEM pollution at WLG, while dust particles originating from desert and Gobi regions in Xinjiang province and the Tibetan Plateau to the west of WLG were responsible for PBM pollution at WLG. This finding is also supported by the significant positive correlation between daily PBM concentration and daily cumulative absorbing aerosol index (AAI) in air masses transported during the preceding 2 d.

Evaluation of regional simulation of surface ozone over Southeast Asia using ground-based observation at two existing Global Atmospheric Watch stations

High level of ground level ozone concentrations was found in most of Southeast Asian (SEA) large cities and often exceeded the national ambient air quality standard. Ozone and PM10 are among of the critical air quality parameters that cause the unhealthy air quality index. Effort to mitigate ozone pollution is greatly complicated due to the photochemistry processes therefore photochemical smog modelling has been widely used. Surface ozone simulation in SEA was done using CHIMERE and weather research forecast (WRF) model. Emission inventory of ozone precursors was done for three countries in the domain, i.e. Indonesia, Thailand and Cambodia. Modelling performance evaluation for meteorological parameters and ozone at the SEA big cities was done in another study. This paper focused on the model evaluation conducted at the two remote sites represented by 2 (two) global atmospheric watch (GAW) remote stations of Bukit Kototabang (BKT) and Danum Valley (DNV). Evaluation result showed an overestimation of observed ozone in BKT while a contradictive result was seen in DNV station which was due to the ozone chemistry and inaccurate estimation of emissions (both anthropogenic and biogenic emission). The evaluation conducted at the remote sites was not even better than that conducted previously at the urban areas. Statistically, only mean normalized gross error and unpaired peak accuracy values that satisfy the criteria for surface ozone modelling suggesting major improvement required for ozone precursors emission inventory data.

Absorption instruments inter-comparison campaign at the Arctic Pallas station

Abstract. Aerosol light absorption was measured during a 1-month field campaign in June–July 2019 at the Pallas Global Atmospheric Watch (GAW) station in northern Finland. Very low aerosol concentrations prevailed during the campaign, which posed a challenge for the instruments' detection capabilities. The campaign provided a real-world test for different absorption measurement techniques supporting the goals of the European Metrology Programme for Innovation and Research (EMPIR) Black Carbon (BC) project in developing aerosol absorption standard and reference methods. In this study we compare the results from five filter-based absorption techniques – aethalometer models AE31 and AE33, a particle soot absorption photometer (PSAP), a multi-angle absorption photometer (MAAP), and a continuous soot monitoring system (COSMOS) – and from one indirect technique called extinction minus scattering (EMS). The ability of the filter-based techniques was shown to be adequate to measure aerosol light absorption coefficients down to around 0.01 Mm−1 levels when data were averaged to 1–2 h. The hourly averaged atmospheric absorption measured by the reference MAAP was 0.09 Mm−1 (at a wavelength of 637 nm). When data were averaged for &gt;1 h, the filter-based methods agreed to around 40 %. COSMOS systematically measured the lowest absorption coefficient values, which was expected due to the sample pre-treatment in the COSMOS inlet. PSAP showed the best linear correlation with MAAP (slope=0.95, R2=0.78), followed by AE31 (slope=0.93). A scattering correction applied to PSAP data improved the data accuracy despite the added noise. However, at very high scattering values the correction led to an underestimation of the absorption. The AE31 data had the highest noise and the correlation with MAAP was the lowest (R2=0.65). Statistically the best linear correlations with MAAP were obtained for AE33 and COSMOS (R2 close to 1), but the biases at around the zero values led to slopes clearly below 1. The sample pre-treatment in the COSMOS instrument resulted in the lowest fitted slope. In contrast to the filter-based techniques, the indirect EMS method was not adequate to measure the low absorption values found at the Pallas site. The lowest absorption at which the EMS signal could be distinguished from the noise was &gt;0.1 Mm−1 at 1–2 h averaging times. The mass absorption cross section (MAC) value measured at a range 0–0.3 Mm−1 was calculated using the MAAP and a single particle soot photometer (SP2), resulting in a MAC value of 16.0±5.7 m2 g−1. Overall, our results demonstrate the challenges encountered in the aerosol absorption measurements in pristine environments and provide some useful guidelines for instrument selection and measurement practices. We highlight the need for a calibrated transfer standard for better inter-comparability of the absorption results.

The innovative development of atmospheric background stations in China: Thoughts and recommendations

Atmospheric background monitoring refers to the long-term observation of atmospheric composition that is well mixed and not affected by local pollution at a fixed location which is far from the influence of human activities. Atmospheric background monitoring can reflect the long-term changes of atmospheric composition caused by human activities on a global or regional scale. Therefore, it plays a very important role in both socioeconomic development and scientific research. Since the 1950s, some observation stations abroad have carried out background observation of the main atmospheric components such as carbon dioxide, ozone and atmospheric heavy metals. Additionally, the Global Ozone Observing System (GO₃OS) and the Background Air Pollution Monitoring Network (BAPMoN) were established by the World Meteorological Organization (WMO) in 1957 and 1968 to fulfill long-term and continuous observation of the chemical constituents of reactive gases, greenhouse gases, aerosols and acid rain. In 1989, WMO integrated GO₃OS and BAPMoN into the Global Atmosphere Watch (GAW). WMO/GAW has achieved great accomplishments owing to its long-term, systematic and accurate observation of the physical and chemical characteristics of atmospheric composition. During the period of 1981 to 2007, China Meteorological Administration (CMA) has built six representative regional GAW (Global Atmosphere Watch) stations, i.e., Shangdianzi (117.12°E, 40.65°N, <sc>293.3 m</sc> asl), Lin’an (119.75°E, 30.28°N, <sc>138.6 m</sc> asl), Longfengshan (127.60°E, 44. 73°N, <sc>331 m</sc> asl), Akedala (87.93°E, 47.10°N, <sc>562 m</sc> asl), Shangri-La (99.73°E, 28.01°N, <sc>3580 m</sc> asl), and Jinsha (114.2°E, 29.63°N, <sc>750 m</sc> asl), following the construction criteria of the GAW regional background stations. In addition, in accordance with the requirements of GAW global background station site selection, the Chinese government and the UN Global Environmental Facility (GEF) jointly invested and established a global GAW station in China, namely, the China GAW Baseline Observatory (CGAWBO), located at Mt. Waliguan (100.89°E, 36.28°N, <sc>3816 m</sc> asl) in Qinghai Province in 1994. These seven global/regional GAW stations build the current operational network of atmospheric background observation stations in China. Thanks to their long-term continous and precise atmospheric composition monitoring data and special representations, the stations at Mt. Waliguan, Shangdianzi, Lin’an, and Longfengshan were selected as the National Field Scientific Observation and Research Stations by the Ministry of Science and Technology of the People’s Republic of China in 2005. It is well known that the long-time series and excellent data on meteorological and atmospheric composition obtained from these seven global/regional GAW stations have played an unique role in China’s efforts on addressing climate change, climate change diplomacy and negotiation, air pollution control, and scientific research. With China’s socioeconomic development stepping into the new era, however, the deficiencies of the current GAW stations have become increasingly significant. Major problems lie in the unbalanced and insufficient development of these stations, as well as in the lack of innovation and demonstration. In this article, the status and the achievements of these seven stations are reviewed and summarized for the first time, followed by the identification and analysis of major problems of development. At last, it is recommended that future endeavors should be concentrated on enhancing the comprehensive observation capability and international cooperation, as well as further improving the construction and capacities of the national field scientific research stations. Besides, it is also suggested that the development of atmospheric background station shall serve China’s national and local development strategy, as well as strengthen its role in China’s progress of ecological civilization.

Analytical study on the primary and secondary organic carbon and elemental carbon in the particulate matter at the high-altitude Monte Curcio GAW station, Italy.

This study provides a thorough investigation of the trends of organic carbon (OC) and elemental carbon (EC) in particulate matter (PM)10 and PM2.5 samples collected at the Monte Curcio Observatory (1780 m a.s.l.), a station of the Global Atmosphere Watch (GAW) program and Global Mercury Observation System (GMOS) network. Although the drawn attention toward these pollutants, there is still a lack of data for southern Italy, and this work is a contribution toward the filling of this gap. PM was sampled daily in 2016 and analyzed by thermo-optical transmittance method, while equivalent black carbon (eBC) concentrations in PM10 were simultaneously measured using a multiangle absorption photometer. The results showed that in PM10, the average values of OC and EC were 1.43 μgC/m3 and 0.12 μgC/m3, whereas in PM2.5, these concentrations were 1.09 μgC/m3 and 0.12 μgC/m3, respectively. We detected a clear seasonal variability in OC and EC with higher concentrations during the warm period. Moreover, the analysis of the OC/EC ratio revealed that most of the carbonaceous aerosol was transported by long-range air masses, as further confirmed by the use of the concentration-weighed trajectory (CWT) model. The mass absorption cross-section at 632 nm of EC (MACEC) over the entire period was 9.67 ± 4.86 m2/g and 8.70 ± 3.18 m2/g in PM2.5 and PM10, respectively, and did not exhibit a clear seasonal variation. The concentrations for OC and EC were also used for the computation of the secondary organic carbon (SOC) content, whose outcomes resulted in a seasonal trend similar to those obtained for OC and EC. As regards the eBC, its weekly pattern showed a slight increase during the weekend in the warm period, consistent with the anthropic activities in the touristic area surrounding the observatory.

Variability of PM10 in a Global Atmosphere Watch Station near the equator

Particulate Matter or aerosol is associated with climate change and global warming through the effect called radiative forcing. Biomass burning aerosol consists of Black Carbon, which has a positive radiative forcing that warms the atmosphere. The goal of this study is to ascertain biomass burning in Sumatera Island’s effect on aerosol concentration. We used Particulate Matter with diameter less than 10 µm (PM10) concentration in the near equator Global Atmosphere Watch Bukit Kototabang (GAW-BKT) and biomass burning in Sumatera Island from Visible Infrared Imaging Radiometer Suite (VIIRS) hotspot count. The statistical and spatial analysis was done for 2014-2018, which include the severe 2015 biomass-burning season. From the analysis of PM10 concentration and hotspot (R2=0.85) and air mass trajectories, biomass burning in Sumatera is the source of PM10 in GAW-BKT. Statistical analysis showed that hotspot in Sumatera, as well as PM10 concentration, follows a monsoonal pattern where the 90th percentile of the hotspot and PM10 concentration fell on dry season. The seasonal variabilities of particulates suggest the strong contribution of biomass open burning which occurred annually with different intensities.

Coastal meteorology on the dispersion of air particles at the Bachok GAW Station

Meteorology over coastal region is a driving factor to the concentration of air particles and reactive gases. This study aims to conduct a research to determine the level of year-round air particles and the interaction of the meteorological driving factors with the particle number and mass in 2018, which is moderately influenced by Southeast Asian haze. We obtained the measurement data for particle number count (PNC), mass, reactive gases, and meteorological factors from a Global Atmospheric Watch (GAW) station located at Bachok Marine Research Center, Bachok, Kelantan, Malaysia. For various timeseries and correlation analyses, a 60-second resolution of the data has been averaged hourly and daily and visualized further. Our results showed the slight difference in particle behavior that is either measured by unit mass or number count at the study area. Diurnal variations showed that particles were generally high during morning and night periods. Spike was observed in August for PM2.5/PNC2.5 and PM10/PNC10 and in November for PMCoarse/PNCCoarse. From a polar plot, the particles came from two distinct sources (e.g., seaside and roadside) at the local scale. Regional wind vector shows two distinct wind-blown directions from northeast and southwest. The air mases were transported from northeast (e.g., Philippines, mainland China, and Taiwan) or southwest (e.g., Sumatra) region. Correlation analysis shows that relative humidity, wind direction, and pressure influence the increase in particles, whereas negative correlation with temperature is observed, and wind speed may have a potential role on the decline of particle concentration. The particles at the study area was highly influenced by the changes in regional wind direction and speed.