Observation and Source Apportionment of Atmospheric Alkaline Gases in Urban Beijing.

Alkaline gases, including NH3, C1-3-amines, C1-3-amides, and C1-3-imines, were measured in situ using a water cluster-CIMS in urban Beijing during the wintertime of 2018, with a campaign average of 2.8 ± 2.0 ppbv, 5.2 ± 4.3, 101.1 ± 94.5, and 5.2 ± 5.4 pptv, respectively. Source apportionment analysis constrained by emission profiles of in-use motor vehicles was performed using a SoFi-PMF software package, and five emission sources were identified as gasoline-powered vehicles (GV), diesel-powered vehicles (DV), septic system emission (SS), soil emission (SE), and combustion-related sources (CS). SS was the dominant NH3 source (60.0%), followed by DV (18.6%), SE (13.1%), CS (4.3%), and GV (4.0%). GV and DV were responsible for 69.9 and 85.2% of C1- and C2-amines emissions, respectively. Most of the C3-amines were emitted from nonmotor vehicular sources (SS = 61.3%; SE = 17.8%; CS = 9.1%). DV accounted for 71.9 and 34.1% of C1- and C2-amides emissions, respectively. CS was mainly comprised of amides and imines, likely originating from the pyrolysis of nitrogen-containing compounds. Our results suggested that motor vehicle exhausts can not only contribute to criteria air pollutants emission but also promote new particle formation, which has not been well recognized and considered in current regulations. Urban residential septic system was the predominant contributor to background NH3. Enhanced NH3 emissions from soil and combustion-related sources were the major cause of PM2.5 buildup during the haze events. Combustion-related sources, together with motor vehicles, were responsible for most of the observed amides and imines and may be of public health concern within the vicinity of these sources.

The missing base molecules in atmospheric acid-base nucleation.

Transformation of low-volatility gaseous precursors to new particles affects aerosol number concentration, cloud formation and hence the climate. The clustering of acid and base molecules is a major mechanism driving fast nucleation and initial growth of new particles in the atmosphere. However, the acid-base cluster composition, measured using state-of-the-art mass spectrometers, cannot explain the measured high formation rate of new particles. Here we present strong evidence for the existence of base molecules such as amines in the smallest atmospheric sulfuric acid clusters prior to their detection by mass spectrometers. We demonstrate that forming (H2SO4)1(amine)1 is the rate-limiting step in atmospheric H2SO4-amine nucleation and the uptake of (H2SO4)1(amine)1 is a major pathway for the initial growth of H2SO4 clusters. The proposed mechanism is very consistent with measured new particle formation in urban Beijing, in which dimethylamine is the key base for H2SO4 nucleation while other bases such as ammonia may contribute to the growth of larger clusters. Our findings further underline the fact that strong amines, even at low concentrations and when undetected in the smallest clusters, can be crucial to particle formation in the planetary boundary layer.

Emissions of Ammonia and Other Nitrogen-Containing Volatile Organic Compounds from Motor Vehicles under Low-Speed Driving Conditions.

Emissions of NH3 and nine nitrogen-containing volatile organic compounds (NVOCs) (C1-3-amines, C1-3-amides, and C1-3-imines) from motor vehicles powered by gasoline, diesel, and natural gas under low-speed driving conditions from roadside in situ measurements were characterized using a water-cluster chemical ionization mass spectrometer and trace gas monitors. The total emission strength of diesel trucks was the greatest followed by those of gasoline cars and natural gas cars. NH3 emission per vehicle was found to be 2-3 orders of magnitude greater than that of all NVOCs, regardless of the type of vehicle. Although much lower than the emissions of amides or imines, emissions of amines were sufficient to produce atmospheric concentrations exceeding the threshold level for amines to enhance atmospheric nucleation by several orders of magnitude. Different engine emission reduction technologies (e.g., three-way catalytic converter vs selective catalytic reduction) can lead to different NH3 and NVOC emission profiles. During the lifetime of a vehicle, its emission level was most likely to increase with its mileage. Source profiles of NH3 and NVOC emissions from the three types of vehicles were also obtained from the measurements. These profiles can be a valuable contribution to the air pollution management system in terms of source apportionment, elucidating the emission contributions from a specific type of vehicle.

Identifying ecosystem service bundles and the spatiotemporal characteristics of trade-offs and synergies in coal mining areas with a high groundwater table.

Understanding the spatiotemporal characteristics of the interactions among ecosystem services (ESs) is a crucial but challenging task for maintaining human well-being and achieving sustainable regional development. However, understanding the spatiotemporal interactions of multiple ESs at different grid scales and within different ecosystem services bundles (ESBs) is relatively limited, particularly in coal mining areas with a high groundwater table (CMA-HGT) where the land use has drastically changed as a result of mining subsidence. This study examines CMA-HGT in Huainan, aiming to identify ESBs and explore the spatiotemporal characteristics of trade-offs/synergies among ESs at distinct grid scales and ESBs. Five ESs relating to provisioning, regulation, and maintenance, including food production (FP), water yield (WY), soil conservation (SC), carbon sequestration (CS), and biodiversity maintenance (BM) were quantified using different biological models during the period 1987-2018. Spatiotemporal trade-offs/synergies among ESs were explored using correlation analysis and significance tests at different scales. The spatiotemporal distributions and main characteristics of distinct ESBs were identified using a self-organizing map (SOM) and Calinski criterion. The interactions among ESs in different ESBs were detected. Relationships between ESs and land use or coal production (CP) were explored using redundancy analysis (RDA). The results demonstrate that spatiotemporal trade-offs were generally observed among provisioning services at distinct grid scales and within different ESBs. Meanwhile, spatiotemporal synergies generally appeared between regulation and maintenance services at distinct grid scales. Interactions among ESs presented temporal dynamic, spatial heterogeneity and scales dependence due to the relationships of FP-BM or SC-CS had changed with the increasing of research scales. Three ESBs-ESB1, ESB2, and ESB3-were identified at a grid of scale of 1000 m, and their spatial locations varied across different periods, but the areas of variation covered less than 24% of the study area. BM was synergistic with FP, WY, SC, and CS; while WY had only a trade-off relationship with FP in ESB1. WY had trade-off relationships with FP, SC, CS, and BM in ESB2. In ESB3, BM was synergistic with FP, SC, and CS; while it was in a trade-off relationship with WY. Cultivated land, construction land and CP were the main driving factors in the WSA, ESB1, ESB2 and ESB3. There was a certain degree of change in the relationships between ESs and land use/CP, and the relationships among ESs at different grid scales and ESBs over time and space, which indicates strong regional heterogeneity and scale dependence. These results can provide detailed guidelines for formulating spatially targeted ecosystem management, restoration programs and ES payment policies.

Seasonal Characteristics of New Particle Formation and Growth in Urban Beijing.

Understanding the atmospheric new particle formation (NPF) process within the global range is important for revealing the budget of atmospheric aerosols and their impacts. We investigated the seasonal characteristics of NPF in the urban environment of Beijing. Aerosol size distributions down to ∼1 nm and H2SO4 concentration were measured during 2018-2019. The observed formation rate of 1.5 nm particles (J1.5) is significantly higher than those in the clean environment, e.g., Hyytiälä, whereas the growth rate is not significantly different. Both J1.5 and NPF frequency in urban Beijing show a clear seasonal variation with maxima in winter and minima in summer, while the observed growth rates are generally within the same range around the year. We show that ambient temperature is a governing factor driving the seasonal variation of J1.5. In contrast, the condensation sink and the daily maximum H2SO4 concentration show no significant seasonal variation during the NPF periods. In all four seasons, condensation of H2SO4 and (H2SO4)n(amine)n clusters contributes significantly to the growth rates in the sub-3 nm size range, whereas it is less important for the observed growth rates of particles above 3 nm. Therefore, other species are always needed for the growth of larger particles.

Responses of gaseous sulfuric acid and particulate sulfate to reduced SO2 concentration: A perspective from long-term measurements in Beijing.

SO2 concentration decreased rapidly in recent years in China due to the implementation of strict control policies by the government. Particulate sulfate (pSO42-) and gaseous H2SO4 (SA) are two major products of SO2 and they play important roles in the haze formation and new particle formation (NPF), respectively. We examined the change in pSO42- and SA concentrations in response to reduced SO2 concentration using long-term measurement data in Beijing. Simulations from the Community Multiscale Air Quality model with a 2-D Volatility Basis Set (CMAQ/2D-VBS) were used for comparison. From 2013 to 2018, SO2 concentration in Beijing decreased by ~81% (from 9.1 ppb to 1.7 ppb). pSO42- concentration in submicrometer particles decreased by ~60% from 2012-2013 (monthly average of ~10 µg·m-3) to 2018-2019 (monthly average of ~4 µg·m-3). Accordingly, the fraction of pSO42- in these particles decreased from 20-30% to <10%. Increased sulfur oxidation ratio was observed both in the measurements and the CMAQ/2D-VBS simulations. Despite the reduction in SO2 concentration, there was no obvious decrease in SA concentration based on data from several measuring periods from 2008 to 2019. This was supported by the increased SA:SO2 ratio with reduced SO2 concentration and condensation sink. NPF frequency in Beijing between 2004 and 2019 remains relatively constant. This constant NPF frequency is consistent with the relatively stable SA concentration in Beijing, while different from some other cities where NPF frequency was reported to decrease with decreased SO2 concentrations.

On-line measurement of fluorescent aerosols near an industrial zone in the Yangtze River Delta region using a wideband integrated bioaerosol spectrometer.

In this work, we present on-line fluorescent aerosol measurements by the wideband integrated bioaerosol spectrometer (WIBS-4A) near an industrial zone in Nanjing, a megacity in the Yangtze-River-Delta (YRD) region. The fieldwork was conducted from April 1 to May 8, 2014. A TSI. 3321 aerosol-particle-sizer (APS) was simultaneously deployed to measure the total number size distribution of aerosol with diameter from 0.8-20 µm. Both WIBS-4A and APS reported similar number concentration and temporal profiles (R2 = 0.72). However, the daily average number of potential bioaerosols was only 0.5 ±â€¯0.2% of the total particles detected by the WIBS-4A and displayed a completely different diurnal profile from that of APS. In addition, WIBS-4A can only provide integrated fluorescent signals, which strongly limited the potential to specifically identify the bioaerosols. Accordingly, hierarchical-agglomerative-cluster-analysis (HACA) was utilized to identify and speciate the potential bioaerosols from the WIBS-4A dataset. By maximizing the total distances among all potential cluster centers, a 12-cluster solution was accepted as the optimum result. These clusters were further identified according to their fluorescent signatures, size, and morphology, i.e., non-bioaerosols, bacteria, and fungal spores and/or pollen fragments. Bacteria were the dominant bioaerosol species detected in this work. The diurnal profiles of bioaerosols correlated very well with relatively humidity (RH), reaching daily maxima around 3 AM~6 AM, indicating the presence of humidity controlled bioaerosol emission mechanism, i.e., bacteria may flourish under moderate ambient temperature, RH, and the absence of UV radiation. The size- and AF-distributions of bioaerosols indicated that bioaerosols normally varied substantially in size and assumed a rather irregular shape. Although the number concentration of bioaerosols was relatively small, most bioaerosols can efficiently serve as ice nuclei by providing rough and irregular surfaces, verified by the observation results. Therefore, WIBS-4A measurements can still be informative for investigations of bioaerosols in the atmosphere, especially when HACA method was incorporated into the data processing.