| Hygroscopicity of atmospheric aerosol particle can influence scattering and absorbing solar radiation, and subsequently altering atmospheric energy balance (direct effects).Additionally, atmospheric aerosol particle can acted as cloud condensation nuclei (CCN)and subsequently changing reflectance and life time of cloud (indirect effects). Aerosol-cloud interaction is the largest uncertainty in accurately predicting climatic change. Over the past decades, a large number of aerosol/cloud studies including laboratory and field measurements, satellite observations,model estimation and intercomparison studies,the uncertainty due to aerosol-cloud interaction has not decreased base on the latest IPCC report. It is necessary to increase our fundamental knowledge of the importance of anthropogenic particles on aerosol-cloud interaction in the climate system and reduce such an uncertainty. A preliminary study on hygroscopicity of diesel emitted particles was performend using a Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) in the indoor smog chamber at Guangzhou Institute of Geochemistry. In addition, the HTDMA was also used to observe hygroscopicity of aerosol particles in urban Guangzhou and the Nanling Mountain Range (1,690 m a.s.l.), South China. Moreover, A single particle aerosol mass spectrometer (SPAMS) coupled with a ground-based counterflow virtual impactor (GCVI) and Scanning Mobility Particle Sizer (SMPS+C) was used to measure the chemical compositions of individual submicron fog/cloud droplet residues at urban Guangzhou and cloud droplet residues at the Nanling Mountain Range. In situ measurement is a good method for capturing accurate parameters, which can improve accurately prediction in climatic system. Main results are listed as follows:1) Hygroscopicity of diesel emitted particles: Hygroscopic parameters ? of Foton and JAC diesel emitted particles were 0.42 and 0.06, respectively, after 3 hours lights on. The? value of fresh and aged particles of JAC diesel were less than 0.02 under idling conditions.The ? decreased from 0.04-0.07 for JAC fresh particles to 0.02-0.04 for aged particles under the control of relative high RH(70%) for chamber. After injectting SO2 into chamber,the ? of JAC diesel-emitted particles was up to 0.69 after 3 hours light.2) Hygroscopicity and chemical composition of aerosol particles were simultaneously measured at urban Guangzhou: Growth factors (GF) of atmospheric dry aerosol particles were measured at relative humidity of 85%. Less-hygroscopic (LH) varied from 0.46 to 0.66. Average growth factor (GF*) varied from 1.25 to 1.33. Number fraction (NF) of the LH mode (NFLH) decreased while GF* increased with diameter increasing. GF* showed the largest value at 09:00, and decreased in the afternoon. Higher GF* (1.24-1.34) was found in northerly air masses compared with southerly air masses (1.25-1.31). Number fraction of K-rich particle type was 0.77 with GF* ? 1.4. Number fration of OC particle type decreased with increasing GF*. Number fration of EC particle type was 0.51 with GF*> 1.4.3) Hygroscopicity of aerosol particles in the Nanling Mountain Range:Hygroscopicity of particles at four diameters (dm) of 30,70, 110 and 250 nm was measured at 83% relative humidity. LH and MH modes were observed in this study. NFLH and GF*of the four dry diameters remained around 0.33 (0.31-0.35) and 1.29 (1.28-1.30),respectively. Hygroscopicity of the 30 nm particles was less influenced by air mass and cloud as well as cloud-free conditions. However, GF* of large particles (dm > 30 nm)reached the maximum value at noon (10:00-16:00), and decreased at late night (22:00-23:00) and early morning (04:00-05:00). Relative to east air mass origination(GF*=1.22-1.34), higher GF* of large particles was found for the south air mass origination(GF*=1.28-1.39). Lower GF* of large particles (GF* = 1.29-1.36) was observed during cloud conditions compared with cloud-free conditions (GF* = 1.33-1.41).4) The observation of individual submicron fog droplet residues at urban Guangzhou:Most of the fog droplet residues were composed of elemental carbon (EC) (67.7%),followed by K-rich (19.2%) and mineral dust/metal (12.3%) particles. Compared with interstitial and ambient aerosols,nitrate enhanced,sulfate was depressed,and ammonium-and organics-containing particles were hardly found in the fog droplet residues during fog events, suggesting that dust and metal particles containing nitrate may be preferentially activated and that ammonium and organics may not play important roles in fog formation in Guangzhou. A direct observational evidence show that trimethylamine and hydroxymethanesulfonate were not found within fog droplet residues, although enhanced gas-to-particle partitioning of these compounds by fog processing. Additionally, higher fraction or intensities of [K]+, [Fe]+, and [SiO3]- were found in fog droplet residues than those in ambient and interstitial particles.5) The measurement of cloud residue particles in the Nanling Mountain Range: (1)The cloud residues were classified into nine particle types: elemental carbon (EC),Potassium-rich (K-rich), Amine, Dust, Pb, Fe, Organic carbon (OC), Sodium-rich (Na-rich)and Other. The largest fraction of the cloud residues was the EC type (49.3% by number),followed by the K-rich type (33.9% by number). Abundant EC cloud residues (up to 60%)were found in air masses from northerly polluted areas. The number fraction (Nf) of the K-rich cloud residues significantly increased (up to 52%) within southwesterly air masses from fire activities in Southeast Asia. The Dust, Fe, Pb, Na-rich and OC particles had a low contribution (0.5-4.1 % by number) to the cloud residues. Sulfate intensity increased in the aged EC and OC cloud residues and decreased in the Dust and Na-rich cloud residues relative to both ambient and interstitial particles. A comparison of cloud residues with interstitial particles indicated that a higher Nf for K-rich particles and a lower Nf for the EC particles were found in the cloud residues; (2) Scavenging efficiency (SE) of aerosol particles varied from 0.01 to 0.63. Higher(0.28-0.63) SE was found in mature stage of cloud event relative to beginning and end of cloud event (0.06-0.30).More variablility for SE of small particles (0.01-0.63) was found in comparison of larger particles (0.03-0.50). |
PDF Full Text Request