Mixing Layer Height Research Articles

Mixing layer transport flux of particulate matter in Beijing, China

Abstract. Quantifying the transport flux (TF) of atmospheric pollutants plays an important role in understanding the causes of air pollution and in making decisions regarding the prevention and control of regional air pollution. In this study, the mixing layer height (MLH) and wind profile were measured by a ceilometer and Doppler wind radar, respectively, and the characteristics of the atmospheric dilution capability were analyzed using these two datasets. The ventilation coefficient (VC) appears to be the highest in the spring (3940±2110 m2 s−1) and lower in the summer (2953±1322 m2 s−1), autumn (2580±1601 m2 s−1) and winter (2913±3323 m2 s−1). Combined with the backscatter measured by the ceilometer, vertical profiles of the PM2.5 concentration were obtained and the PM2.5 TF in the mixing layer was calculated. The TF was the highest in the spring at 4.33±0.69 mg m−1 s−1 and lower in the summer, autumn and winter, when the TF values were 2.27±0.42, 2.39±0.45 and 2.89±0.49 mg m−1 s−1, respectively. Air pollutants transport mainly occurs between 14:00 and 18:00 LT. The TF was large in the pollution transition period (spring: 5.50±4.83 mg m−1 s−1; summer: 3.94±2.36 mg m−1 s−1; autumn: 3.72±2.86 mg m−1 s−1; winter: 4.45±4.40 mg m−1 s−1) and decreased during the heavy pollution period (spring: 4.69±4.84 mg m−1 s−1; summer: 3.39±1.77 mg m−1 s−1; autumn: 3.01±2.40 mg m−1 s−1; winter: 3.25±2.77 mg m−1 s−1). Our results indicate that the influence of the air pollutants transport in the southern regions should receive more focus in the transition period of pollution, while local emissions should receive more focus in the heavy pollution period.

Seasonal Characteristics of Atmospheric Boundary Layer and its Associated Dynamics over Central India

Atmospheric boundary-layer studies have applications in lower tropospheric processes, air pollution meteorology, weather prediction and climate monitoring. Despite this, very few studies are available over tropics, especially over central India. Here, we analyse, high resolution vertical profiles of meteorological parameters corresponding to fully developed mixed layer obtained using balloon borne radiosonde to study characteristics of atmospheric boundary layer over Nagpur (21.15 °N, 79.15 °E). Study reveals that, within the mixed layer, variation in RH is very less (within 20%) while above mixed layer, large variations are seen. Back trajectory analysis confirms that the moist days (dry days) are associated with the transport of air masses from the Arabian Sea (from arid locations). Mixed layer heights derived through gradients in Virtual Potential Temperature (VPT) showed highest values during Pre monsoon (2564 ± 867 m) and lowest (788 ± 477 m) in Monsoon season. Specific Humidity varies in the range from 0 to 10 g/kg during pre-monsoon and 0–20 g/kg during monsoon season. D-theta exhibits lowest values in monsoon and highest values during pre-monsoon season while Parcel saturation pressure difference exhibits highest values in monsoon and lowest values during pre-monsoon season. During the monsoon and early post monsoon there is a presence of high moist static energy (Theta-e ~ 365 K) at the surface and moderate during mid-winter. We have examined, for the first time, the spatial (vertical) coherence of VPT using a novel technique of auto correlation analysis. Coherence length scales, derived with this method are found to be Maximum (1129 ± 48 m) in winter and minimum (694 ± 281 m) in Pre monsoon season.

A Review of Techniques for Diagnosing the Atmospheric Boundary Layer Height (ABLH) Using Aerosol Lidar Data

The height of the atmospheric boundary layer (ABLH) or the mixing layer height (MLH) is a key parameter characterizing the planetary boundary layer, and the accurate estimation of that is critically important for boundary layer related studies, which include air quality forecasts and numerical weather prediction. Aerosol lidar is a powerful remote sensing instrument frequently used to retrieve the ABLH through detecting the vertical distributions of aerosol concentration. Presently available methods for ABLH determination from aerosol lidar are summarized in this review, including a lot of classical methodologies as well as some improved versions of them. Some new recently developed methods applying advanced techniques such as image edge detection, as well as some new methods based on multi-wavelength lidar systems, are also summarized. Although a lot of techniques have been proposed and have already given reasonable results in several studies, it is impossible to recommend a technique which is suitable in all atmospheric scenarios. More accurate instantaneous ABLH from robust techniques is required, which can be used to estimate or improve the boundary layer parameterization in the numerical model, or maybe possible to be assimilated into the weather and environment models to improve the simulation or forecast of weather and air quality in the future.

Implementation of a 2D Wavelet Method to Probe Mixed Layer Height Using Lidar Observations

A new method was developed to estimate mixed layer (ML) height with light detection and ranging (lidar) observations using a 2Dimensional (2D) wavelet method, which can consider the diurnal variation characteristics of ML height. Ideal signals and real lidar observations in Shanghai, China were used to evaluate the new method. The results showed that the new method is insensitive to the type of wavelet filters. The estimated ML heights obtained by the 2D wavelet method agreed well with both of the previous methods developed for the ML height probing using lidar, including the gradient method, the 1D-wavelet method, the standard deviation method, and the conventional radiosonde method. The primary differences among the results obtained via the different lidar methods occurred in the early morning or later afternoon; when the ML is well mixed, very small differences were observed among the different lidar methods. The new method showed better determination skills than other methods when compared to the radiosonde observation results. It also performed well when there were missing profiles or observation errors and it made the new method suitable for operations where data quality control may be missed.

Hurricane Boundary Layer Height Relative to Storm Motion from GPS Dropsonde Composites

This study investigates the asymmetric distribution of hurricane boundary layer height scales in a storm-motion-relative framework using global positioning system (GPS) dropsonde observations. Data from a total of 1916 dropsondes collected within four times the radius of maximum wind speed of 37 named hurricanes over the Atlantic basin from 1998 to 2015 are analyzed in the composite framework. Motion-relative quadrant mean composite analyses show that both the kinematic and thermodynamic boundary layer height scales tend to increase with increasing radius in all four motion-relative quadrants. It is also found that the thermodynamic mixed layer depth and height of maximum tangential wind speed are within the inflow layer in all motion-relative quadrants. The inflow layer depth and height of the maximum tangential wind are both found to be deeper in the two front quadrants, and they are largest in the right-front quadrant. The difference in the thermodynamic mixed layer depth between the front and back quadrants is smaller than that in the kinematic boundary layer height. The thermodynamic mixed layer is shallowest in the right-rear quadrant, which may be due to the cold wake phenomena. The boundary layer height derived using the critical Richardson number ( R i c ) method shows a similar front-back asymmetry as the kinematic boundary layer height.

Analysis of aerosol scattering properties and PM10 concentrations at a mountain site influenced by mineral dust transport

Aerosol scattering properties (ASP) i.e., scattering and backscattering coefficients (σsp, σbsp, 525 nm), scattering Ångström exponent (SAE, 450–635 nm) and backscatter ratio (b, 525 nm) along with PM10 concentrations were measured from November 2015 to October 2016 at a mountain site (1558 m a.s.l) located in the southwestern Mediterranean. ASP and PM10 average values obtained for the whole period were: 26.2 Mm−1, 3.5 Mm−1, 1.42, 0.139 and 12.4 μg/m3, respectively. The study was aimed at analyzing: a) the seasonal variability of the measured parameters, b) the impact of mineral dust from North Africa on PM10 and optical properties and c) the variation of ASP values and PM10 concentrations as a function of the mixing layer height. The extensive scattering properties had values ∼35% higher during the warm period, while SAE and b were similar during both the cold and warm seasons. σsp and σbsp increased under Saharan dust events (SDE). In contrast, SAE and b values showed a decrease due to the increase in coarse particle concentrations during this type of event. On non-event days, the lowest values of σsp and PM10 were recorded under free troposphere (FT) conditions (10.5 Mm−1, 3 μg/m3). Conversely, SAE recorded its highest value (∼2.00) under these conditions, pointing to a predominance of fine particles in this layer. Average values of σsp and PM10 increased with the increase in the height of the Planetary Boundary Layer (PBL), while the SAE value progressively decreased to a steady value of 1.50–1.60. The average value of the mass scattering efficiency (MSE) during the study period was 1.35 m2/g.

Atmospheric boundary layer dynamics from balloon soundings worldwide: CLASS4GL v1.0

Abstract. The coupling between soil, vegetation and atmosphere is thought to be crucial in the development and intensification of weather extremes, especially meteorological droughts, heat waves and severe storms. Therefore, understanding the evolution of the atmospheric boundary layer (ABL) and the role of land–atmosphere feedbacks is necessary for earlier warnings, better climate projection and timely societal adaptation. However, this understanding is hampered by the difficulties of attributing cause–effect relationships from complex coupled models and the irregular space–time distribution of in situ observations of the land–atmosphere system. As such, there is a need for simple deterministic appraisals that systematically discriminate land–atmosphere interactions from observed weather phenomena over large domains and climatological time spans. Here, we present a new interactive data platform to study the behavior of the ABL and land–atmosphere interactions based on worldwide weather balloon soundings and an ABL model. This software tool – referred to as CLASS4GL (http://class4gl.eu, last access: 27 May 2018) – is developed with the objectives of (a) mining appropriate global observational data from ∼15 million weather balloon soundings since 1981 and combining them with satellite and reanalysis data and (b) constraining and initializing a numerical model of the daytime evolution of the ABL that serves as a tool to interpret these observations mechanistically and deterministically. As a result, it fully automizes extensive global model experiments to assess the effects of land and atmospheric conditions on the ABL evolution as observed in different climate regions around the world. The suitability of the set of observations, model formulations and global parameters employed by CLASS4GL is extensively validated. In most cases, the framework is able to realistically reproduce the observed daytime response of the mixed-layer height, potential temperature and specific humidity from the balloon soundings. In this extensive global validation exercise, a bias of 10.1 m h−1, −0.036 K h−1 and 0.06 g kg−1 h−1 is found for the morning-to-afternoon evolution of the mixed-layer height, potential temperature and specific humidity. The virtual tool is in continuous development and aims to foster a better process understanding of the drivers of the ABL evolution and their global distribution, particularly during the onset and amplification of weather extremes. Finally, it can also be used to scrutinize the representation of land–atmosphere feedbacks and ABL dynamics in Earth system models, numerical weather prediction models, atmospheric reanalysis and satellite retrievals, with the ultimate goal of improving local climate projections, providing earlier warning of extreme weather and fostering a more effective development of climate adaptation strategies. The tool can be easily downloaded via http://class4gl.eu (last access: 27 May 2018) and is open source.

Climatology of mixing layer height in China based on multi-year meteorological data from 2000 to 2013

Atmospheric aerosol levels are high in different regions of China. Changes in atmospheric stability and mixing layer height (MLH) may affect the vertical aerosol distribution during pollution events. Here, we continuous studied the spatiotemporal distribution of MLH in China over 2000–2013 to characterize the regional-scale properties of atmospheric boundary layers. MLH was larger in the Southern Coastal and Southeastern China (1241.5 ± 73.5 and 632.7 ± 61.8 m, respectively), but lower in Eastern and Southwestern China (518.1 ± 63.6 and 462.7 ± 88.5 m, respectively). We divided the monitoring stations into 11 regions; these regions could be classified into three types with an increasing linear trend (95% confidence level), with a decreasing linear trend (95% confidence level), and with fluctuation changes. In all regions, MLH was higher in spring and summer than in autumn and winter. The spatial distribution of the diurnal MLH increased significantly at 1400 BJT (Beijing time) in all regions, with the strongest radiation being noted during the daytime. Higher levels of PM2.5 with corresponding lower MLH were noted during winter, indicating that lower MLH could confine the pollutant diffusion to near the surface. By contrast, in spring, higher MLH could be potentially due to the dynamic condition. In general, the poor air quality days occurred more frequently in winter than in other seasons. As the air quality worsened, most MLH showed a decreasing trend in almost all regions. This work provides information that aids in further understanding not only MLH distribution in China but also specific PM–MLH interaction to facilitate regional atmospheric environment monitoring and prediction.

Effects of Continental Clouds on Surface Aitken and Accumulation Modes

AbstractRelationships between clouds and surface aerosol are investigated at the Oklahoma Atmospheric Radiation Measurements Southern Great Plains site. Cloud chemical transformations, coalescence, and Brownian capture increase material within cloud droplets. Then when cloud droplets evaporate, as they often do, their residuals are larger than unnucleated particles. This creates a bimodal particle size distribution by moving some Aitken mode (25‐ to 100‐nm diameter) particles to the accumulation mode (100‐ to 825‐nm diameter). Clouds also block solar radiation that causes photochemical reactions that produce small particles that grow by coagulation and condensation into the Aitken mode. Highly significant positive correlations of remotely sensed cloud fraction (cf) with time‐lagged Aitken and accumulation mode mean particle diameter (mpd) isolated the effects of cloud processing on both modes. Positive correlations of cf with accumulation concentrations and negative correlations of cf with Aitken concentrations also provided evidence of cloud processing. Photochemical production of very small particles under clear daylight skies worked together with cloud processing to enhance Aitken mpd and concentration correlations with cf. Cloud‐processed aerosol was evident only during daylight and when the boundary layer mixing height exceeded the remotely sensed cloud base altitude. Greater cf, especially consecutive high cf hours increased accumulation and Aitken mpd and accumulation concentrations while it decreased Aitken concentrations. Lower cf, especially consecutive hours of no clouds, decreased overall mpd and did not enhance the accumulation mode. All of these results implicated clouds as a source of the accumulation mode, and thus, clouds seemed to explain bimodal aerosol over the mid‐North American continent.

Ceilometer Monitoring of Boundary-Layer Height and Its Application in Evaluating the Dilution Effect on Air Pollution

The dilution effect caused by boundary-layer evolution over land has strong influences on air quality. Accurate and continuous measurements of the boundary-layer height over urban areas are therefore needed for complete air-quality assessments. Commercial ceilometers, in combination with reliable and simple methodologies, can be used to retrieve the mixed-layer height, and represent a means of obtaining information on vertical mixing and atmospheric structure above cities. Here, we evaluate various retrieval algorithms based on the gradient method against high-temporal-resolution radiosonde observations. Based on the results, we propose a simple algorithm by using the gradient method, the correction of background noise and the moving averages, with the minimum number of parameters that need to be adjusted to the local properties and the instrument itself. The algorithm is adjusted for Seoul, Korea, and improves the retrieval performance by reducing high-frequency noise. The algorithm is used to investigate the relationship between the evolution of the daytime mixed-layer height and air pollution under a two-layer mixing model where changes in concentration depend only on the urban boundary-layer growth and air entrainment from the free atmosphere. Using 2 months of ceilometer retrievals of mixed-layer height and air-quality data from across the city, we find strong negative correlations for primary emitted pollutants such as NO2, CO, SO2, and particulate matter smaller than 10 µm, and a modest positive correlation for O3. The results provide insight into the significant influence of urban boundary-layer evolution on Seoul’s air quality.

Synergistic effect of the occurrence of African dust outbreaks on atmospheric pollutant levels in the Madrid metropolitan area

The occurrence of African dust outbreaks over specific areas of the Mediterranean basin has been associated with increases in the PM10 concentration levels and also in the mortality rates. Different hypothesis have been proposed in the last years to explain the processes by which African dust storms generates negative health effect over urban areas in southern Europe but are still not clear. Some authors have suggested the existence of an interaction between air pollutants from local sources and the occurrence of African dust outbreaks, with a consequent increase in the risk of mortality due to exposure to these anthropogenic emissions. This study sought to identify such a synergistic effect in the Madrid metropolitan area. To this end, an assessment of the influence of African dust on air quality levels, the vertical structure of the atmosphere over Madrid and daily mortality was carried out. Our results indicated that African dust caused a reduction of the mixing layer height and the surface wind speed, by reducing the amount of solar radiation reaching the ground. These facts favored the accumulation of air pollutants emissions from local anthropogenic sources. Moreover, when the dust contribution to PM10 levels exceeded a threshold value (8 μg/m3), particulate matter mass (PM10, PM2.5) and number (ultra-fine particles) concentration as well as levels of gaseous air pollutants (CO, NO and NO2) registered at urban-background and urban-traffic monitoring sites, increased with statistical significance. In these conditions, it was found a statistically significant increase in risk of daily mortality in the PM10 exposure. Hence, ambient air in Madrid was more toxic during African dust events of increasing intensity due to this synergistic effect. Because it can be envisaged that the frequency, duration and intensity of dust storms will increase in the north of Africa due to climate change, it will be a priority to put forward and assess proposals to mitigate the adverse effects on health, focused on the reduction of air pollutant emissions from local sources, as well as proposals regarding the adaptation of the population in urban areas across the Mediterranean basin.

Improved estimation of air pollutant emissions from landing and takeoff cycles of civil aircraft in China

Civil aircraft emissions during landing and takeoff (LTO) are important air pollutant sources, but have been given insufficient attention in China. Accurate estimation of these emissions is limited by a lack of important parameters, such as detailed flight information and the dynamic time in climb and approach modes during LTO that are dependent on mixing layer height (MLH). We developed a flight-time/flight-height relationship using real-time height information in Aircraft Meteorological Data Relay data, and then calculated the actual time for each flight in those two modes based on the actual MLH from meteorological observation. Hourly emissions of civil aircraft were then estimated based on the database of each flight. Total emissions of NOx, CO, SO2, HC and PM from LTO cycles of domestic flights in China during 2015 were 37.78 Gg, 30.25 Gg, 12.00 Gg, 2.38 Gg and 0.75 Gg, respectively. Substantial monthly, daily and hourly variations of emissions due to the flight schedule as well as MLH were calculated. Large differences were found between the new estimation and emissions calculated based on traditional method. Compared with the emissions estimated based on default parameter obtained from International Civil Aviation Organization, the average difference of annual emission among airports with new estimation for various pollutants was approximately 30.3% in climb mode and 81.4% in approach mode; compared with the emissions estimated based on the method proposed by China National Guide, the average difference of annual emission among airports were 37.4% (NOx), 8.4% (CO), 73.1% (HC) and 58.1% (PM) during LTO process. The monthly airport-specific emissions per LTO were also proposed. These can provide necessary and meaningful support for the revision of the values in National Guide.

Case study of the effects of aerosol chemical composition and hygroscopicity on the scattering coefficient in summer, Xianghe, southeast of Beijing, China

The aerosol scattering coefficient is mainly affected by various factors, such as aerosol chemical composition, hygroscopicity and relative humidity. A comprehensive observation of the chemical and physical properties of aerosols was conducted in Xianghe, southeast of Beijing, from June 15 to 26, 2018. Five specific cases were analysed during this observation: (1) rainy (RA); (2) low visibility during the day (LD); (3) high visibility during the day (HD); (4) low visibility at night (LN); and (5) high visibility at night (HN). The mass percentages of a secondary inorganic aerosol (nitrate, sulfate and ammonium) measured with a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) were 64.5% and 68.3% during LD and LN, which were higher than those (63.6% and 46.1%) observed during HD and HN, respectively. The mass percentages of secondary organic aerosol (SOA) and primary organic aerosol (POA) to organic aerosol were 76.6% and 23.4%, respectively, during LD. The hygroscopic parameters κ were 0.59 and 0.60 during LD and LN, which were slightly higher than those (0.57 and 0.58) observed during HD and HN, respectively, indicating that the variation of aerosol chemical composition had a limited impact on hygroscopicity. The average proportion, measured with a single particle aerosol mass spectrometer (SPAMS), of biomass burning, dust, heavy metal, soot-like, sea salt, secondary aerosols and other particles were 12.3%, 2.9%, 16.2%, 36.1%, 8.8%, 21.0% and 2.7%. The average proportions of soot-like and secondary aerosols were 42.4% and 19.2% from 0.2 to 1.0 μm. Although the variation and height of the mixing layer were similar between LD and HD, clouds reduced the solar radiation during LD, which caused a higher relative humidity (RH) (67.5%) than that (45.9%) observed during HD. A larger wind speed below 850 hpa during HN caused the mixing layer height (MLH) to reach 1910 m, which resulted in a lower RH (64.8%) than that (68.0%) observed during LN. The light scattering enhancement factors f(RH) during low visibility events were almost greater than those observed during high visibility events, regardless of they were measured during the day (0–9.7%) or night (0–13.1%). The aerosol hygroscopic growth factor (GF) maintained a similar trend with RH, indicating that RH was the main factor affecting the hygroscopic growth of the aerosol, resulting in the decrease in visibility.

Summertime Urban Mixing Layer Height over Sofia, Bulgaria

Mixing layer height (MLH) is a crucial parameter for air quality modelling that is still not routinely measured. Common methods for MLH determination use atmospheric profiles recorded by radiosonde but this process suffers from coarse temporal resolution since the balloon is usually launched only twice a day. Recently, cheap ceilometers are gaining popularity in the retrieval of MLH diurnal evolution based on aerosol profiles. This study presents a comparison between proprietary (Jenoptik) and freely available (STRAT) algorithms to retrieve MLH diurnal cycle over an urban area. The comparison was conducted in the summer season when MLH is above the full overlapping height of the ceilometer in order to minimize negative impact of the biaxial LiDAR’s drawback. Moreover, fogs or very low clouds which can deteriorate the ceilometer retrieval accuracy are very unlikely to be present in summer. The MLHs determined from the ceilometer were verified against those measured from the radiosonde, which were estimated using the parcel, lapse rate, and Richardson methods (the Richardson method was used as a reference in this study). We found that the STRAT and Jenoptik methods gave lower MLH values than radiosonde with an underestimation of about 150 m and 650 m, respectively. Additionally, STRAT showed some potential in tracking the MLH diurnal evolution, especially during the day. A daily MLH maximum of about 2000 m was found in the late afternoon (18–19 LT). The Jenoptik algorithm showed comparable results to the STRAT algorithm during the night (although both methods sometimes misleadingly reported residual or advected layers as the mixing layer (ML)). During the morning transition the Jenoptik algorithm outperformed STRAT, which suffers from abrupt changes in MLH due to integrated layer attribution. However, daytime performance of Jenoptik was worse, especially in the afternoon when the algorithm often cannot estimate any MLH (in the period 13–16 LT the method reports MLHs in only 15–30% of all cases). This makes day-to-day tracing of MLH diurnal evolution virtually impracticable. This problem is possibly due to its early version (JO-CloVis 8.80, 2009) and issues with real-time processing of a single profile combined with the low signal-to-noise ratio of the ceilometer. Both LiDAR-based algorithms have trouble in the evening transition since they rely on aerosol signature which is more affected by the mixing processes in the past hours than the current turbulent mixing.

Vertical characterization of aerosol optical properties and brown carbon in winter in urban Beijing, China

Abstract. Aerosol particles are of importance in the Earth's radiation budget since they scatter and absorb sunlight. While extensive studies of aerosol optical properties have been conducted at ground sites, vertical measurements and characterization are very limited in megacities. In this work, we present simultaneous real-time online measurements of aerosol optical properties at ground level and at 260 m on a meteorological tower from 16 November to 13 December in 2016 in Beijing along with measurements of continuous vertical profiles during two haze episodes. The average (±1σ) scattering and absorption coefficients (bsca and babs; λ=630 nm) were 337.6 (±356.0) and 36.6 (±33.9) Mm−1 at 260 m, which were 26.5 % and 22.5 % lower than those at ground level. Single scattering albedo (SSA), however, was comparable between the two heights, with slightly higher values at ground level (0.89±0.04). Although bsca and babs showed overall similar temporal variations between ground level and 260 m, the ratios of 260 m to ground varied substantially from less than 0.4 during the clean stages of haze episodes to > 0.8 in the late afternoon. A more detailed analysis indicates that vertical profiles of bsca, babs, and SSA in the low atmosphere were closely related to the changes in meteorological conditions and mixing layer height. The mass absorption cross section (MAC) of equivalent black carbon (eBC, λ=630 nm) varied substantially from 9.5 to 13.2 m2 g−1 in winter in Beijing, and it was strongly associated with the mass ratio of coating materials on refractory BC (rBC) to rBC (MR), and also the oxidation degree of organics in rBC-containing particles. Our results show that the increases in MAC of eBC in winter were mainly caused by photochemically produced secondary materials. Light absorption of organic carbon (brown carbon, BrC) was also important in winter, which on average accounted for 46 (±8.5) % and 48 (±9.3) % of the total absorption at 370 nm at ground level and 260 m, respectively. A linear regression model combined with positive matrix factorization analysis was used to show that coal combustion was the dominant source contribution of BrC (48 %–55 %) followed by biomass burning (17 %) and photochemically processed secondary organic aerosol (∼20 %) in winter in Beijing.

Intercomparison of Mixing Layer Heights from the National Weather Service Ceilometer Test Sites and Collocated Radiosondes

AbstractA network of automated weather stations (AWS) with ceilometers can be used to detect sky conditions, aerosol dispersion, and mixing layer heights, in addition to the routine surface meteorological parameters (temperature, pressure, humidity, etc.). Currently, a dense network of AWSs that observe all of these parameters does not exist in the United States even though networks of them with ceilometers exist. These networks normally use ceilometers for determining only sky conditions. Updating AWS networks to obtain those nonstandard observations with ceilometers, especially mixing layer height, across the United States would provide valuable information for validating and improving weather/climate forecast models. In this respect, an aerosol-based mixing layer height detection method, called the combined-hybrid method, is developed and evaluated for its uncertainty characteristics for application in the United States. Four years of ceilometer data from the National Weather Service Ceilometer Proof of Concept Project taken in temperate, maritime polar, and hot/arid climate regimes are utilized in this evaluation. Overall, the method proved to be a strong candidate for estimating mixing layer heights with ceilometer data, with averaged uncertainties of 237 ± 398 m in all tested climate regimes and 69 ± 250 m when excluding the hot/arid climate regime.

Airborne Particulate Pollution Measured in Bangladesh from 2014 to 2017

ABSTRACT Recently, the World Health Organization ranked Narayanganj, Chittagong, and Dhaka among the top 25, 40, and 45 cities, respectively, for high ambient PM2.5 concentrations. Bangladesh has instituted an air quality monitoring system operated by the Department of Environment. PM2.5 and PM10 were measured hourly from January 2014 through December 2017 in Dhaka, Gazipur, Narayanganj, Chittagong, Sylhet, and Barisal. All sites registered concentrations for both pollutants that exceeded the 24-h Bangladesh National Ambient Air Quality Standards. The particulate matter (PM) concentrations varied significantly seasonally and with different diel patterns from city to city. The highest concentrations were observed during the winter, typically when wind speeds and mixed layer heights are low and pollutant concentrations are increased by transport from the northwest. The PM2.5 concentrations from the 1st quarters of 2014 and 2015 were compared to assess whether political unrest that appeared to reduce vehicular moment to very low levels affected the observed values. However, the PM2.5 concentrations were statistically similar at the Dhaka, Narayanganj, and Sylhet sites and different for the Gazipur, Chittagong, and Barisal locations. Thus, the PM2.5 concentrations during the political unrest in the 1st quarter of 2015 were not consistently lower across the measurement sites. These results indicate that vehicular emission contributions to PM2.5 concentrations are smaller than in the past, which agrees with recent source apportionment studies showing that brick kilns have become the dominant source of PM.

Mixed Layer Height Calculated from Mie Lidar Data over Tsukuba and Saga: Diurnal and Seasonal Variations and Comparison with Radiosonde and Objective Analysis Data

Mixed Layer Height Calculated from Mie Lidar Data over Tsukuba and Saga: Diurnal and Seasonal Variations and Comparison with Radiosonde and Objective Analysis Data

Development and application of a twin open-top chambers method to measure soil HONO emission in the North China Plain

HONO (nitrous acid) is a crucial precursor for tropospheric OH radicals, and its sources are not well understood. In the past decade, soil was proven to be a potential source for HONO. However, more field measurements of soil HONO emission flux are needed to explore the mechanism and its impact on regional air quality. Here, we developed a system based on twin open-top chambers (OTCs) and wet chemical methods to measure HONO emission flux from agricultural soil in the North China Plain (NCP). The performance of the OTC system was tested under laboratory and field measurement conditions. The results showed that the system could reflect the strength (>90%) and variation of gas emission with an average residence time of 4–5 min. The greenhouse effect and chemical reaction interference in the chamber was proven to have no significant influence on the HONO flux measurement. Field measurement revealed that agricultural soil before fertilization was an important source of HONO. The emission flux showed radiation-dependent or temperature-dependent variation, with a peak of 3.21 ng m−2 s−1 at noontime that could account for approximately 67 pptv h−1 of the missing HONO source under an assumed mixing layer height of 300 m. Fertilization substantially accelerated HONO emission, which was rationally attributed to biological processes including nitrification. Considering the high fertilization rate in the NCP and other similar regions in China, HONO emission from agricultural soil likely has enormous impact on regional photochemistry and air quality, suggesting that more research should be conducted on this aspect.

Aerosol and pollutant characteristics in Delhi during a winter research campaign.

Urban areas in developing countries are major sources of carbonaceous aerosols and air pollutants, pointing out the need for a detailed assessment of their levels and origin close to the source. A multi-instrument research campaign was performed in Delhi during December 2015-February 2016 aimed at exploring the pollution levels and the contribution of various sources to particulate matter (PM) concentrations, black carbon (BC) aerosols, and trace gases. The weak winds (< 5-6ms-1) along with the shallow boundary layer favoured the formation of thick and persistent fog conditions, which along with the high BC (24.4 ± 12.2μgm-3) concentrations lead to the formation of smog. Very high pollution levels were recorded during the campaign, with mean PM10, PM2.5, CO, NO, and O3 concentrations of 245.5 ± 109.8μgm-3, 145.5 ± 69.5μgm-3, 1.7 ± 0.5ppm, 7.9 ± 2.3ppb, and 31.3 ± 18.4ppb, respectively. This study focuses on examining the daily/diurnal cycles of the aerosol optical properties (extinction, scattering, absorption coefficients, single scattering albedo), as well as of PM and other pollutant concentrations, along with changes in meteorology (mixing-layer height and wind speed). In addition, the hot-spot pollution sources in the greater Delhi area were determined via bivariate plots and conditional bivariate probability function (CBPF), while the distant sources were examined via the concentration weighted trajectory (CWT) analysis. The results show that the highest aerosol absorption and scattering coefficients, PM, and trace gas concentrations are detected for weak winds (< 2ms-1) with a preference for eastern directions, revealing high contribution from local sources and accumulation of pollutants within urban Delhi.