Aerosol liquid water content (ALWC) has an important effect on atmospheric visibility as well as heterogeneous chemical reactions. In this paper, we used the data size-resolved particle hygroscopic ...growth factor, and particle number size distribution (PNSD) obtained from H-TDMA and SMPS to compute ALWC at the Guangzhou Panyu site from the winter of 2014 and the spring of 2015. The corresponding results were relatively consistent with the trend for ALWCISO calculated from the ISORROPIA II thermodynamic equilibrium model based on the measurement of aerosol water-soluble ionic compositions obtained from MARGA, with a linear fit yielding an R2 value of 0.76. The fact that ALWCHTDMA was somewhat higher than ALWCISO at low RH values was at least partially attributable to the fact that effects resulting from organic matter hygroscopicity were not taken into account when computing ALWCISO. In sensitivity testing, ambient relative humidity, PNSD and particle hygroscopicity were all found to affect ALWC, in that order. Particles of different modes made different contributions to ALWC with the contributions of nuclear, Aitken, accumulation and coarse modes assessed at <1%, 3%, 85% and 12%, respectively, indicating that the contribution of accumulation mode particles to ALWC dominated among all the aerosol particle modes. During clean processes, decreases in relative humidity and PM2.5 both resulted in a decrease in ALWC. During the pollution processes, calm winds caused local particle accumulation, with ALWC increasing as RH increased. Intraday trends in ALWC and relative humidity were consistent, with minimum mean values observed in the afternoon due to low ambient relative humidity inhibiting an increase in ALWC. However, diurnal variation of aerosol hygroscopicity and ALWC tended to be somewhat anti-correlated, indicating that diurnal changes in aerosol hygroscopicity are not a primary factor resulting in ambient AWLC changes.
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•H-TDMA and SMPS data were used to calculate aerosol liquid water content (ALWC) and performed a comparison with ALWC modeled by ISORROPIA II.•Ambient relative humidity, PNSD and aerosol hygroscopicity were determined to be most prominent of affecting ALWC, in that order•The contribution of accumulation mode particles to ALWC dominated among all the aerosol particle modes.
•The measured light-scattering enhancement factors (f(RH)sp) agreed well with those simulated by Mie model.•The f(RH) of extinction, scattering and backscattering are more sensitive to Gf than PNSD ...and BC volume fraction.•For core-shell mixture, the f(RH)absp increases with Gf and reaches the highest value when Gf is around 1.3•Aerosol hygroscopicity could result in stronger “Towmey effect” with elevated RH.
The hygroscopic enhancement factor of extinction (a), scattering (b), backscattering (c) absorption (d), HBF (e) and SSA (f) calculated from the Mie model for external (black dotes), homogeneously internal (green dotes), and core-shell (red dotes) mixing states. Display omitted
Both the effects of aerosol hygroscopicity and mixing state on aerosol optical properties were analyzed using ground-based measurements and a Mie model in this study. The sized-resolved particle hygroscopic growth factor at RH = 90% (Gf(90%)) and the enhancement factor for the scattering coefficients (f(RH)sp) were measured by a self-constructed Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) and two nephelometers in parallel (PNEPs) respectively from 22nd February to 18th March 2014 in the Pearl River Delta, China. In addition, the particle number size distribution (PNSD) and BC mass concentration (MBC) were measured simultaneously.
During the observation period, the f(RH)sp increased sharply along with increasing RH (40%–85%) and the value of f(80%)sp was 1.77 ± 0.18. The mean Gf(90%) for all particles are 1.44 (80 nm), 1.48 (110 nm), 1.52 (150 nm) and 1.55 (200 nm), and the mean Gf(90%) for more-hygroscopic particles are 1.58 (80 nm), 1.63 (110 nm), 1.66 (150 nm) and 1.67 (200 nm) respectively. Based on Gf, PNSD and MBC, the enhancement factor of the aerosol optical properties (extinction (f(RH)ep), scattering (f(RH)sp), backscattering (f(RH)hbsp), absorption (f(RH)absp), and hemispheric backscatter fraction (f(RH)hbsp)) were calculated under three aerosol mixing state assumptions. The results show that the calculated f(80%)sp values agreed well with the ones measured by PNEPs, illustrating that the Gf size distribution fittings are reasonable. The f(RH)ep, f(RH)sp and f(RH)hbsp increased along with increasing RH for three mixtures, while f(RH)HBF decreased. The f(RH)absp increased for the homogenously internal mixture, but remained stable for the external mixture. For the core-shell mixture, the f(RH)absp increased from RH = 0 to 75% and then decreased, due to a decrease of light entering the BC core. The enhancement factor of aerosol direct radiative forcing (f(RH)Fr) increased sharply as the RH elevated for the external mixing state. However, f(RH)Fr increased or decreased along with the elevated RH for the homogenously internal mixture and the core-shell mixture depending on initial value of the aerosol direct radiative forcing (∆Fr) in a dry condition.
The lidar ratio (LR) is a key parameter for the retrieval of atmospheric optical parameters from lidar equations. In this study, we simulated the optical parameters to investigate the impact factors ...of the LR using a three-component optical aerosol assumption based on the Mie model. The simulated LR was generally related to the overall particle size of the aerosols, the proportion of elemental carbon (EC), as well as aerosol mixing states and hygroscopicity. The LR was positively correlated with the particle size and volume fraction of elemental carbon (fEC). The LR increased more than three-fold with the increase in fEC from 0% to 40%. The LR of the core-shell (CS) mixing state and homogeneously internal (INT) mixing state was greater than that of the external (EXT) mixing state. The LR of all mixing states increased monotonically with hygroscopicity when the fEC was below 10%, while the LR of the core-shell mixing state (homogeneously internal mixing state) initially decreased (increased) and then increased (decreased) with increasing hygroscopicity when the fEC was more than 20%. These results will help in selecting a reasonable LR for practical applications.
Hygroscopic growth can significantly affect size distribution and activation of aerosol particles, as well as their effects on human health, atmospheric visibility, and climate. In this study, an ...H-TDMA (Hygroscopic Tandem Differential Mobility Analyzer) was utilized to measure hygroscopic growth factor and mixing state of aerosol particles at the CAWNET station in Panyu, Guangzhou, China. A statistical analysis of the results show that, at relative humidity (RH) of 90%, for less-hygroscopic particles of 40–200 nm in diameter, the growth factor (gLH) was around 1.13, while the number fraction (NFLH) varied between 0.41 ± 0.136 and 0.26 ± 0.078; for more-hygroscopic particles, the growth factor (gMH) varied between 1.46 and 1.55 with the average equivalent ammonium sulfate ratio (ɛAS) ranging from 0.63 to 0.68. The differences in ɛAS among particle of different sizes reveal that more-hygroscopic inorganic salts, such as ammonium sulfate and ammonium nitrate, are of more effective condensation growth for Aitken mode particles. A combined analysis of the probability density function of growth factor (Gf-PDF) and simultaneous meteorological data shows that during clean periods with air masses moving from the north, the particles are more likely to have homogeneous chemical composition, while during polluted or pollution accumulation periods, variations in mean number weighted growth factor (gmean) and NFMH become more pronounced, indicating that locally-emitted aerosol particles tend to be in an externally mixed state and contain a certain proportion of less-hygroscopic particles. This study can help improve our understanding of aerosol hygroscopicity and its impact on the atmospheric visibility and environment.
•Size-resolved measurement of hygroscopicity of submicrometer particles were done.•Aerosol hygroscopicity in the Pearl River Delta differs from other megacities in China.•Aerosol hygroscopicity has a significant diurnal variation, and closely related to air mass origin.
In 2019–2020, an array weather radar (AWR) network consisting of seven X-band phased-array radars (PARs), with a detection spatial resolution of 30 m and a temporal resolution of 30 s, was built in ...the city of Foshan in China’s Guangdong Province. The detection time deviation in the same space is within 5 s. Through variational data assimilation, the three-dimensional wind field inside the storm can be obtained. This study selected instances of hail, thunderstorms, strong winds, and short-duration heavy precipitation in 2020 to conduct a detailed analysis. The results show the following: (1) The fine detection ability enables phased-array radars to detect the complete evolution process of convective storms, including development, strengthening, and weakening, providing a useful reference for judging the future variation trends of convective storms. (2) Through evolutionary analysis of the three-dimensional wind field, the dynamic mechanisms of storm strengthening and weakening could be obtained, which could serve as a reference to predict the development of storms. The gust wind index and convection index calculated based on the three-dimensional wind field could provide advanced warning for nowcasting. When the gust wind index was greater than 263, the probability of gale-force wind (above 17.0 m/s) was determined to be high. Moreover, the warning could be provided 10–20 min in advance. A convection index greater than 35 and the presence of concentrated contour lines were found to be conducive to the strengthening and formation of a convection, and the warning could be provided 20 min in advance. These results show that the application of PAR can provide important technical support for nowcasting severe convective weather.
We detected a severe haze process in Guangzhou area with lidar and microwave radiometer, performed an inversion to get boundary layer height by wavelet covariance transform, and analyzed the ...correlation between meteorological factors of boundary layer and visibility from the perspective of dynamical and thermodynamic structures. Our results indicate that the boundary layer height shows significant daily changes, consistent with ground visibility variation. During the cleaning process, the boundary layer height exceeded 1 km; during severe haze, the height was only 500 m. Temperature gradient of 50-100 m, which was 30 h lag, was remarkably correlated with visibility, with the correlation coefficient of 0.77. High layer visibility （255 m） and low layer stability were significantly anticorrelation, and the maximum anticorrelation coefficient was up to -0.76 in cleaning days and -0.49 in haze days. In the related boundary layer meteorological factors, surface ventilation coefficient was linearly correlated with ground visibility, with the greatest correlation coefficient of 0.88. The correlation coefficients of boundary layer height, ground wind velocity, relative humidity and ground visibility were 0.76, 0.67, and -0.77, respectively. There was a strong correlation between different meteorological factors. The dominant meteorological factor during this haze process was surface ventilation coefficient. In the area without boundary layer height sounding, ground visibility and wind ve- locity could be used to estimate boundary layer height.
An EF1 tornado associated with tropical cyclone (TC) Ewiniar hit Dali Town, Foshan, Guangdong Province at 06:03 UTC on June 8, 2018, and the first special tornado warning was issued to five towns at ...05:05 UTC. This article utilizes minute-scale observations from an X-band dual-polarization radar and measurements from an S-band Doppler radar to resolve the polarization characteristics associated with this tornado. In addition, second-scale atmospheric pressure data obtained from micropressure gauge and NCEP FNL (Final) Operational Global Analysis data are used to investigate the synoptic conditions and features of gravity waves (GWs). The conspicuous features of the descending reflectivity core, Doppler velocity couplet, Z <inline-formula><tex-math notation="LaTeX">_{\text{DR}}</tex-math></inline-formula> arc, K <inline-formula><tex-math notation="LaTeX">_{\text{DP}}</tex-math></inline-formula> foot, and the separation of the Z <inline-formula><tex-math notation="LaTeX">_{\text{DR}}</tex-math></inline-formula> arc and K <inline-formula><tex-math notation="LaTeX">_{\text{DP}}</tex-math></inline-formula> foot are detailed to quantify the tornadic evolution. The amplitude fluctuation of the GWs suddenly increased to 77.3 Pa, 2 h before the tornado occurred. Two focus regions with K <inline-formula><tex-math notation="LaTeX">_{\text{DP}}</tex-math></inline-formula> values greater than 6<inline-formula><tex-math notation="LaTeX">^\circ</tex-math></inline-formula>/km are discussed by combining the Doppler velocity couplet and Z <inline-formula><tex-math notation="LaTeX">_{\text{DR}}</tex-math></inline-formula> arc. The separation distance of the Z <inline-formula><tex-math notation="LaTeX">_{\text{DR}}</tex-math></inline-formula> arc and K <inline-formula><tex-math notation="LaTeX">_{\text{DP}}</tex-math></inline-formula> foot was approximately 2.1 km. The appearance of these features may be indicative of fundamental processes intrinsic to tornado storms.
The physical and chemical properties of aerosol particles were investigated during two dust storm events that occurred in March 20–21, 2010 (DS1) and April 26–27, 2010 (DS2), respectively, at ...Shanghai, China. Highest hourly mass concentrations of particulate matters with less than 2.5μm (PM2.5) and 10μm (PM10) in aerodynamic diameter reached 469 and 1700μgm−3, respectively, in DS1, whereas the corresponding highest values for PM2.5 and PM10 were 94 and 236μgm−3, respectively, in DS2. Profiles of hourly concentrations of water soluble ions show that anthropogenic air masses preceded dust plume by an interval of 10h during the two dust storm events. Anthropogenic air masses were characterized with high concentrations of SO42−, NO3−, and NH4+, whereas dust plume was dominated by Ca2+ in water soluble components. Together with back trajectories of air parcels arriving at Shanghai, analysis of surface weather chart shows that DS1 was characterized with the arrival of a cold front at Shanghai. In contrast, a chief feature of the cold front stimulated DS2 was that the cold-front did not extend to Shanghai, and dust particles traveled following the front and were transported to Shanghai by strong southeastward airstream although the front did not extend to Shanghai. Our results suggest that Asian dust particles are not homogeneously mixed with anthropogenic pollutants and consecutive transport of anthropogenic air masses and dust plumes occurs.
•Asian dust particles were not homogeneously mixed with anthropogenic pollutants.•Consecutive transport of anthropogenic and dust plumes occurred by an interval of 10hours.•Dust particles can be transported to Shanghai by strong airstreams between a high and a low.
We present measurements of submicron aerosols in Tijuana, Mexico during the Cal–Mex 2010 field campaign. A suite of aerosol instrumentations were deployed, including a hygroscopic–volatility tandem ...differential mobility analyzer (HV–TDMA), aerosol particle mass analyzer (APM), condensation particle counter (CPC), cavity ring-down spectrometer (CRDS), and nephelometer to measure the aerosol size distributions, effective density, hygroscopic growth factors (HGF), volatility growth factors (VGF), and optical properties. The average mass concentration of PM0.6 is 10.39 ± 7.61 μg m−3, and the derived average black carbon (BC) mass concentration is 2.87 ± 2.65 μg m−3. There is little new particle formation or particle growth during the day, and the mass loading is dominated by organic aerosols and BC, which on average are 37% and 27% of PM1.0, respectively. For four particle sizes of 46, 81, 151, and 240 nm, the measured particle effective density, HGFs, and VGFs exhibit distinct diurnal trends and size-dependence. For smaller particles (46 and 81 nm), the effective density distribution is unimodal during the day and night, signifying an internally mixed aerosol composition. In contrast, larger particles (151 and 240 nm) exhibit a bi-modal effective density distribution during the daytime, indicating an external mixture of fresh BC and organic aerosols, but a unimodal distribution during the night, corresponding to an internal mixture of BC and organic aerosols. The smaller particles show a noticeable diurnal trend in the effective density distribution, with the highest effective density (1.70 g cm−3) occurring shortly after midnight and the lowest value (0.90 g cm−3) occurring during the afternoon, corresponding most likely to primary organic aerosols and BC, respectively. Both HGFs and VGFs measured are strongly size-dependent. HGFs increase with increasing particle size, indicating that the largest particles are more hygroscopic. VGFs decrease with increasing particle size, indicating that larger particles are more volatile. The hygroscopicity distributions of smaller particles (46 and 81 nm) are unimodal, with a HGF value close to unity. Large particles typically exhibit a bi-modal distribution, with a non-hygroscopic mode and a hygroscopic mode. For all particle sizes, the VGF distributions are bimodal, with a primary non-volatile mode and a secondary volatile mode. The average extinction, scattering, and absorption coefficients are 86.04, 63.07, and 22.97 Mm−1, respectively, and the average SSA is 0.75. Our results reveal that gasoline and diesel vehicles produce a significant amount of black carbon particles in this US–Mexico border region, which impacts the regional environment and climate.
•Comprehensive measurements of aerosol properties during the Cal–Mex 2010 study.•An average black carbon mass concentration of 2.87 ± 2.65 μg m−3.•Gasoline and diesel vehicles produce a significant amount of BC particles.
Recent studies show that the rapid increases in urbanization and human activities in the PRD region have important impacts on regional air quality. In addition to local anthropogenic emissions which ...are major driving forces for poor air quality in this region, biomass burning in Southeast Asia has also important contribution on aerosol and ozone concentrations in the PRD region. In this paper, this effect is analyzed by using satellite data, ground measurements and models. MODIS aerosol optical depth (AOD) distribution in March 2006 shows a clear enhancement in AOD between Southeast Asia and the PRD region. With detail wind analysis, two distinguished conditions are classified, i.e., Condition-1 (PRD is under influence of the biomass burning from Southeast Asia) and Condition-2 (PRD is not under influence of the biomass burning from Southeast Asia). The characterizations of aerosol, UV, and ozone in Guangzhou city (located in the PRD region) under these two conditions are analyzed. The analyses suggest that aerosols and CO concentrations are higher in Condition-1 than in Condition-2; while the UV intensity and O
3 concentrations are lower in Condition-1 than in Condition-2. This result indicates that in Condition-1, the enhanced aerosol concentrations from the Southeast Asia biomass burning produce reduction of UV intensity, and thus decreases the formation of ozone in Guangzhou.
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