Search Results
A broad supersaturation scanning (BS2) approach for rapid measurement of aerosol particle hygroscopicity and cloud condensation nuclei activity
2016, Su, Hang, Cheng, Yafang, Ma, Nan, Wang, Zhibin, Wang, Xiaoxiang, Pöhlker, Mira L., Nillius, Björn, Wiedensohler, Alfred, Pöschl, Ulrich
The activation and hygroscopicity of cloud condensation nuclei (CCN) are key to the understanding of aerosol–cloud interactions and their impact on climate. They can be measured by scanning the particle size and supersaturation in CCN measurements. The scanning of supersaturation is often time-consuming and limits the temporal resolution and performance of CCN measurements. Here we present a new approach, termed the broad supersaturation scanning (BS2) method, in which a range of supersaturation is simultaneously scanned, reducing the time interval between different supersaturation scans. The practical applicability of the BS2 approach is demonstrated with nano-CCN measurements of laboratory-generated aerosol particles. Model simulations show that the BS2 approach may also be applicable for measuring CCN activation of ambient mixed particles. Due to its fast response and technical simplicity, the BS2 approach may be well suited for aircraft and long-term measurements. Since hygroscopicity is closely related to the fraction of organics/inorganics in aerosol particles, a BS2-CCN counter can also serve as a complementary sensor for fast detection/estimation of aerosol chemical compositions.
Influence of biomass burning on mixing state of sub-micron aerosol particles in the North China Plain
2017, Kecorius, Simonas, Ma, Nan, Teich, Monique, van Pinxteren, Dominik, Zhang, Shenglan, Gröβ, Johannes, Spindler, Gerald, Müller, Konrad, Iinuma, Yoshiteru, Hu, Min, Herrmann, Hartmut, Wiedensohler, Alfred
Particulate emissions from crop residue burning decrease the air quality as well as influence aerosol radiative properties on a regional scale. The North China Plain (NCP) is known for the large scale biomass burning (BB) of field residues, which often results in heavy haze pollution episodes across the region. We have been able to capture a unique BB episode during the international CAREBeijing-NCP intensive field campaign in Wangdu in the NCP (38.6°N, 115.2°E) from June to July 2014. It was found that aerosol particles originating from this BB event showed a significantly different mixing state compared with clean and non-BB pollution episodes. BB originated particles showed a narrower probability density function (PDF) of shrink factor (SF). And the maximum was found at shrink factor of 0.6, which is higher than in other episodes. The non-volatile particle number fraction during the BB episode decreased to 3% and was the lowest measured value compared to all other predefined episodes. To evaluate the influence of particle mixing state on aerosol single scattering albedo (SSA), SSA at different RHs was simulated using the measured aerosol physical-chemical properties. The differences between the calculated SSA for biomass burning, clean and pollution episodes are significant, meaning that the variation of SSA in different pollution conditions needs to be considered in the evaluation of aerosol direct radiative effects in the NCP. And the calculated SSA was found to be quite sensitive on the mixing state of BC, especially at low-RH condition. The simulated SSA was also compared with the measured values. For all the three predefined episodes, the measured SSA are very close to the calculated ones with assumed mixing states of homogeneously internal and core-shell internal mixing, indicating that both of the conception models are appropriate for the calculation of ambient SSA in the NCP.
Sea salt emission, transport and influence on size-segregated nitrate simulation: A case study in northwestern Europe by WRF-Chem
2016, Chen, Ying, Cheng, Yafang, Ma, Nan, Wolke, Ralf, Nordmann, Stephan, Schüttauf, Stephanie, Ran, Liang, Wehner, Birgit, Birmili, Wolfram, van der Gon, Hugo A.C. Denier, Mu, Qing, Barthel, Stefan, Spindler, Gerald, Stieger, Bastian, Müller, Konrad, Zheng, Guang-Jie, Pöschl, Ulrich, Su, Hang, Wiedensohler, Alfred
Sea salt aerosol (SSA) is one of the major components of primary aerosols and has significant impact on the formation of secondary inorganic particles mass on a global scale. In this study, the fully online coupled WRF-Chem model was utilized to evaluate the SSA emission scheme and its influence on the nitrate simulation in a case study in Europe during 10–20 September 2013. Meteorological conditions near the surface, wind pattern and thermal stratification structure were well reproduced by the model. Nonetheless, the coarse-mode (PM1 − 10) particle mass concentration was substantially overestimated due to the overestimation of SSA and nitrate. Compared to filter measurements at four EMEP stations (coastal stations: Bilthoven, Kollumerwaard and Vredepeel; inland station: Melpitz), the model overestimated SSA concentrations by a factor of 8–20. We found that this overestimation was mainly caused by overestimated SSA emissions over the North Sea during 16–20 September. Over the coastal regions, SSA was injected into the continental free troposphere through an “aloft bridge” (about 500 to 1000 m above the ground), a result of the different thermodynamic properties and planetary boundary layer (PBL) structure between continental and marine regions. The injected SSA was further transported inland and mixed downward to the surface through downdraft and PBL turbulence. This process extended the influence of SSA to a larger downwind region, leading, for example, to an overestimation of SSA at Melpitz, Germany, by a factor of ∼ 20. As a result, the nitrate partitioning fraction (ratio between particulate nitrate and the summation of particulate nitrate and gas-phase nitric acid) increased by about 20 % for the coarse-mode nitrate due to the overestimation of SSA at Melpitz. However, no significant difference in the partitioning fraction for the fine-mode nitrate was found. About 140 % overestimation of the coarse-mode nitrate resulted from the influence of SSA at Melpitz. In contrast, the overestimation of SSA inhibited the nitrate particle formation in the fine mode by about 20 % because of the increased consumption of precursor by coarse-mode nitrate formation.
Strong impact of wildfires on the abundance and aging of black carbon in the lowermost stratosphere
2018, Ditas, Jeannine, Ma, Nan, Zhang, Yuxuan, Assmann, Denise, Neumaier, Marco, Riede, Hella, Karu, Einar, Williams, Jonathan, Scharffe, Dieter, Wang, Qiaoqiao, Saturno, Jorge, Schwarz, Joshua P., Katich, Joseph M., McMeeking, Gavin R., Zahn, Andreas, Hermann, Markus, Brenninkmeijer, Carl A. M., Andreae, Meinrat O., Pöschl, Ulrich, Su, Hang, Cheng, Yafang
Wildfires inject large amounts of black carbon (BC) particles into the atmosphere, which can reach the lowermost stratosphere (LMS) and cause strong radiative forcing. During a 14-month period of observations on board a passenger aircraft flying between Europe and North America, we found frequent and widespread biomass burning (BB) plumes, influencing 16 of 160 flight hours in the LMS. The average BC mass concentrations in these plumes (∼140 ng·m−3, standard temperature and pressure) were over 20 times higher than the background concentration (∼6 ng·m−3) with more than 100-fold enhanced peak values (up to ∼720 ng·m−3). In the LMS, nearly all BC particles were covered with a thick coating. The average mass equivalent diameter of the BC particle cores was ∼120 nm with a mean coating thickness of ∼150 nm in the BB plume and ∼90 nm with a coating of ∼125 nm in the background. In a BB plume that was encountered twice, we also found a high diameter growth rate of ∼1 nm·h−1 due to the BC particle coatings. The observed high concentrations and thick coatings of BC particles demonstrate that wildfires can induce strong local heating in the LMS and may have a significant influence on the regional radiative forcing of climate.
Helicopter-borne observations of the continental background aerosol in combination with remote sensing and ground-based measurements
2018, Düsing, Sebastian, Wehner, Birgit, Seifert, Patric, Ansmann, Albert, Baars, Holger, Ditas, Florian, Henning, Silvia, Ma, Nan, Poulain, Laurent, Siebert, Holger, Wiedensohler, Alfred, Macke, Andreas
This paper examines the representativeness of ground-based in situ measurements for the planetary boundary layer (PBL) and conducts a closure study between airborne in situ and ground-based lidar measurements up to an altitude of 2300 m. The related measurements were carried out in a field campaign within the framework of the High-Definition Clouds and Precipitation for Advancing Climate Prediction (HD(CP)2) Observational Prototype Experiment (HOPE) in September 2013 in a rural background area of central Europe. The helicopter-borne probe ACTOS (Airborne Cloud and Turbulence Observation System) provided measurements of the aerosol particle number size distribution (PNSD), the aerosol particle number concentration (PNC), the number concentration of cloud condensation nuclei (CCN-NC), and meteorological atmospheric parameters (e.g., temperature and relative humidity). These measurements were supported by the ground-based 3+2 wavelength polarization lidar system PollyXT, which provided profiles of the particle backscatter coefficient (σbsc) for three wavelengths (355, 532, and 1064 nm). Particle extinction coefficient (σext) profiles were obtained by using a fixed backscatter-to-extinction ratio (also lidar ratio, LR). A new approach was used to determine profiles of CCN-NC for continental aerosol. The results of this new approach were consistent with the airborne in situ measurements within the uncertainties. In terms of representativeness, the PNSD measurements on the ground showed a good agreement with the measurements provided with ACTOS for lower altitudes. The ground-based measurements of PNC and CCN-NC are representative of the PBL when the PBL is well mixed. Locally isolated new particle formation events on the ground or at the top of the PBL led to vertical variability in the cases presented here and ground-based measurements are not entirely representative of the PBL. Based on Mie theory (Mie, 1908), optical aerosol properties under ambient conditions for different altitudes were determined using the airborne in situ measurements and were compared with the lidar measurements. The investigation of the optical properties shows that on average the airborne-based particle light backscatter coefficient is 50.1 % smaller for 1064 nm, 27.4 % smaller for 532 nm, and 29.5 % smaller for 355 nm than the measurements of the lidar system. These results are quite promising, since in situ measurement-based Mie calculations of the particle light backscattering are scarce and the modeling is quite challenging. In contrast, for the particle light extinction coefficient we found a good agreement. The airborne-based particle light extinction coefficient was just 8.2 % larger for 532 nm and 3 % smaller for 355 nm, for an assumed LR of 55 sr. The particle light extinction coefficient for 1064 nm was derived with a LR of 30 sr. For this wavelength, the airborne-based particle light extinction coefficient is 5.2 % smaller than the lidar measurements. For the first time, the lidar ratio of 30 sr for 1064 nm was determined on the basis of in situ measurements and the LR of 55 sr for 355 and 532 nm wavelength was reproduced for European continental aerosol on the basis of this comparison. Lidar observations and the in situ based aerosol optical properties agree within the uncertainties. However, our observations indicate that a determination of the PNSD for a large size range is important for a reliable modeling of aerosol particle backscattering.
Significant concentrations of nitryl chloride sustained in the morning: Investigations of the causes and impacts on ozone production in a polluted region of northern China
2016, Tham, Yee Jun, Wang, Zhe, Li, Qinyi, Yun, Hui, Wang, Weihao, Wang, Xinfeng, Xue, Likun, Lu, Keding, Ma, Nan, Bohn, Birger, Li, Xin, Kecorius, Simonas, Größ, Johannes, Shao, Min, Wiedensohler, Alfred, Zhang, Yuanhang, Wang, Tao
Nitryl chloride (ClNO2) is a dominant source of chlorine radical in polluted environment, and can significantly affect the atmospheric oxidative chemistry. However, the abundance of ClNO2 and its exact role are not fully understood under different environmental conditions. During the summer of 2014, we deployed a chemical ionization mass spectrometer to measure ClNO2 and dinitrogen pentoxide (N2O5) at a rural site in the polluted North China Plain. Elevated mixing ratios of ClNO2 (> 350 pptv) were observed at most of the nights with low levels of N2O5 (< 200 pptv). The highest ClNO2 mixing ratio of 2070 pptv (1 min average) was observed in a plume from a megacity (Tianjin), and was characterized with a faster N2O5 heterogeneous loss rate and ClNO2 production rate compared to average conditions. The abundant ClNO2 concentration kept increasing even after sunrise, and reached a peak 4 h later. Such highly sustained ClNO2 peaks after sunrise are discrepant from the previously observed typical diurnal pattern. Meteorological and chemical analysis shows that the sustained ClNO2 morning peaks are caused by significant ClNO2 production in the residual layer at night followed by downward mixing after breakup of the nocturnal inversion layer in the morning. We estimated that ∼ 1.7–4.0 ppbv of ClNO2 would exist in the residual layer in order to maintain the observed morning ClNO2 peaks at the surface site. Observation-based box model analysis show that photolysis of ClNO2 produced chlorine radical with a rate up to 1.12 ppbv h−1, accounting for 10–30 % of primary ROx production in the morning hours. The perturbation in total radical production leads to an increase of integrated daytime net ozone production by 3 % (4.3 ppbv) on average, and with a larger increase of 13 % (11 ppbv) in megacity outflow that was characterized with higher ClNO2 and a relatively lower oxygenated hydrocarbon (OVOC) to non-methane hydrocarbon (NMHC) ratio.
Evaluation of the size segregation of elemental carbon (EC) emission in Europe: Influence on the simulation of EC long-range transportation
2016, Chen, Ying, Cheng, Ya-Fang, Nordmann, Stephan, Birmili, Wolfram, van der Gon, Hugo A.C. Denier, Ma, Nan, Wolke, Ralf, Wehner, Birgit, Sun, Jia, Spindler, Gerald, Mu, Qing, Pöschl, Ulrich, Su, Hang, Wiedensohler, Alfred
Elemental Carbon (EC) has a significant impact on human health and climate change. In order to evaluate the size segregation of EC emission in the EUCAARI inventory and investigate its influence on the simulation of EC long-range transportation in Europe, we used the fully coupled online Weather Research and Forecasting/Chemistry model (WRF-Chem) at a resolution of 2 km focusing on a region in Germany, in conjunction with a high-resolution EC emission inventory. The ground meteorology conditions, vertical structure and wind pattern were well reproduced by the model. The simulations of particle number and/or mass size distributions were evaluated with observations at the central European background site Melpitz. The fine mode particle concentration was reasonably well simulated, but the coarse mode was substantially overestimated by the model mainly due to the plume with high EC concentration in coarse mode emitted by a nearby point source. The comparisons between simulated EC and Multi-angle Absorption Photometers (MAAP) measurements at Melpitz, Leipzig-TROPOS and Bösel indicated that the coarse mode EC (ECc) emitted from the nearby point sources might be overestimated by a factor of 2–10. The fraction of ECc was overestimated in the emission inventory by about 10–30 % for Russia and 5–10 % for Eastern Europe (e.g., Poland and Belarus). This incorrect size-dependent EC emission results in a shorter atmospheric life time of EC particles and inhibits the long-range transport of EC. A case study showed that this effect caused an underestimation of 20–40 % in the EC mass concentration in Germany under eastern wind pattern.
A novel method for deriving the aerosol hygroscopicity parameter based only on measurements from a humidified nephelometer system
2017, Kuang, Ye, Zhao, Chunsheng, Tao, Jiangchuan, Bian, Yuxuan, Ma, Nan, Zhao, Gang
Aerosol hygroscopicity is crucial for understanding roles of aerosol particles in atmospheric chemistry and aerosol climate effects. Light-scattering enhancement factor f (RH, λ) is one of the parameters describing aerosol hygroscopicity, which is defined as f (RH, λ) = δsp(RH, λ)=δsp(dry, λ), where δsp(RH, λ) or δsp(dry, λ) represents δsp at wavelength λ under certain relative humidity (RH) or dry conditions. Traditionally, an overall hygroscopicity parameter κ can be retrieved from measured f (RH, λ), hereinafter referred to as κf(RH), by combining concurrently measured particle number size distribution (PNSD) and mass concentration of black carbon. In this paper, a new method is proposed to directly derive κf(RH) based only on measurements from a three-wavelength humidified nephelometer system. The advantage of this newly proposed approach is that κf(RH) can be estimated without any additional information about PNSD and black carbon. This method is verified with measurements from two different field campaigns. Values of κf(RH) estimated from this new method agree very well with those retrieved by using the traditional method: all points lie near the 1 : 1 line and the square of correlation coefficient between them is 0.99. The verification results demonstrate that this newly proposed method of deriving κf(RH) is applicable at different sites and in seasons of the North China Plain and might also be applicable in other regions around the world.
Variation of CCN activity during new particle formation events in the North China Plain
2016, Ma, Nan, Zhao, Chunsheng, Tao, Jiangchuan, Wu, Zhijun, Kecorius, Simonas, Wang, Zhibin, Größ, Johannes, Liu, Hongjian, Bian, Yuxuan, Kuang, Ye, Teich, Monique, Spindler, Gerald, Müller, Konrad, van Pinxteren, Dominik, Herrmann, Hartmut, Hu, Min, Wiedensohler, Alfred
The aim of this investigation was to obtain a better understanding of the variability of the cloud condensation nuclei (CCN) activity during new particle formation (NPF) events in an anthropogenically polluted atmosphere of the North China Plain (NCP). We investigated the size-resolved activation ratio as well as particle number size distribution, hygroscopicity, and volatility during a 4-week intensive field experiment in summertime at a regional atmospheric observatory in Xianghe. Interestingly, based on a case study, two types of NPF events were found, in which the newly formed particles exhibited either a higher or a lower hygroscopicity. Therefore, the CCN activity of newly formed particles in different NPF events was largely different, indicating that a simple parameterization of particle CCN activity during NPF events over the NCP might lead to poor estimates of CCN number concentration (NCCN). For a more accurate estimation of the potential NCCN during NPF events, the variation of CCN activity has to be taken into account. Considering that a fixed activation ratio curve or critical diameter are usually used to calculate NCCN, the influence of the variation of particle CCN activity on the calculation of NCCN during NPF events was evaluated based on the two parameterizations. It was found that NCCN might be underestimated by up to 30 % if a single activation ratio curve (representative of the region and season) were to be used in the calculation; and might be underestimated by up to 50 % if a fixed critical diameter (representative of the region and season) were used. Therefore, we suggest not using a fixed critical diameter in the prediction of NCCN in NPF. If real-time CCN activity data are not available, using a proper fixed activation ratio curve can be an alternative but compromised choice.
Heterogeneous N2O5 uptake coefficient and production yield of ClNO2 in polluted northern China: Roles of aerosol water content and chemical composition
2018, Tham, Yee Jun, Wang, Zhe, Li, Qinyi, Wang, Weihao, Wang, Xinfeng, Lu, Keding, Ma, Nan, Yan, Chao, Kecorius, Simonas, Wiedensohler, Alfred, Zhang, Yuanhang, Wang, Tao
Heterogeneous uptake of dinitrogen pentoxide (N2O5) and production of nitryl chloride (ClNO2) are important nocturnal atmospheric processes that have significant implications for the production of secondary pollutants. However, the understanding of N2O5 uptake processes and ClNO2 production remains limited, especially in China. This study presents a field investigation of the N2O5 heterogeneous uptake coefficient (γ(N2O5)) and ClNO2 production yield (ϕ) in a polluted area of northern China during the summer of 2014. The N2O5 uptake coefficient and ClNO2 yield were estimated by using the simultaneously measured ClNO2 and total nitrate in 10 selected cases, which have concurrent increases in the ClNO2 and nitrate concentrations and relatively stable environmental conditions. The determined γ(N2O5) and ϕ values varied greatly, with an average of 0.022 for γ(N2O5) (±0.012, standard deviation) and 0.34 for ϕ (±0.28, standard deviation). The variations in γ(N2O5) could not be fully explained by the previously derived parameterizations of N2O5 uptake that consider nitrate, chloride, and the organic coating. Heterogeneous uptake of N2O5 was found to have a strong positive dependence on the relative humidity and aerosol water content. This result suggests that the heterogeneous uptake of N2O5 in Wangdu is governed mainly by the amount of water in the aerosol, and is strongly water limited, which is different from most of the field observations in the US and Europe. The ClNO2 yield estimated from the parameterization was also overestimated comparing to that derived from the observation. The observation-derived ϕ showed a decreasing trend with an increasing ratio of acetonitrile to carbon monoxide, an indicator of biomass burning emissions, which suggests a possible suppressive effect on the production yield of ClNO2 in the plumes influenced by biomass burning in this region. The findings of this study illustrate the need to improve our understanding and to parameterize the key factors for γ(N2O5) and ϕ to accurately assess photochemical and haze pollution.