Analyses Of The Characteristics Of Aerosols In Pearl River Delta Based On The MARG Data

In this paper, we study the physical and chemical characteristics of aerosols in the PearlRiver Delta, by using the high temporal resolution MARGA data. We conducted instrumentalobservation experiments, and the results showed that the water-soluble fraction accounted for44%in PM_2.5. Since the trend of MARGA is consistent with that of PM_2.5, the water-soluble partmeasured by MARGA is reliable. The data from SO₂analyzer is higher than that from theMARGA, with approximately28.7%higher. The uncertainty of MARGA in measuring SO₂may results in underestimation. In the Pearl River Delta, positive and negative ions of aerosol fitwell, with the square of the correlation coefficient as high as0.9795. A large proportion of theaerosols exist as the form of （NH₄）₂SO₄, followed by NH₄HSO₄and NH₄NO3. The averageconcentration of total water-soluble component in the Pearl River Delta is18.6μg/m³, indicatingthat the water-soluble component counts for40.6%in PM_2.5. In the rainy season （April toSeptember）, the total concentration of the water-soluble component is16.2μg/m³, accounting for48%in PM_2.5. During the dry season （October to March）, the total concentration of thewater-soluble component is20.9μg/m³, accounting for40.6%in PM_2.5, which is lower than thatfor the rainy season. NO3-, SO₄^2-=and NH₄+account for89.4%of the total water-solublecomponent, with NO3-, SO₄^2-=and NH₄+count for23.4%,43.5%and22.5%, respectively. Theannual average concentration of HNO₃is1.43μg/m³, and the diurnal variation is featured by twoor three peaks, and the concentration for rainy season is lower than that for dry season. Thediurnal variation HONO is obviously featured by two peaks, and maintains a high concentrationof at night. NO3-has no obvious diurnal variation, but has obvious seasonal variation, with theconcentration higher in the dry season and lower in the rainy season. The monthly variation ofSO₄^2-=and NH₄⁺are similar to that of NO3-, with the concentration distinct between dry and rainyseason. The metal element counts for about7.2%of the water-soluble component. Theconcentration of K+is lower in the rainy season than in the dry season. The concentration of Ca²⁺does not exhibit obvious seasonal and monthly variation, but the concentration in March ishigher than other months, resulting from sandstorms. The diurnal and seasonal variation of Mg²⁺ is similar to Ca²⁺.We analyzed three chemical processes including the Cl loss, the dust storm and the haze.The results showed that the Cl loss in Xichong （XC） is56.9%, in Zhuzilin （ZZL） is48.0%. Thesea salt Cl loss in XC and ZZL are mainly due to the reaction of NaCl and HNO₃, while inGuangzhou Nancun station industrial sources may also play an important role besides thereaction of NaCl and HNO₃. In addition, the Cl loss is more likely to occur when the relativehumidity is lower. Sandstorms affect the acidic of aerosols: the acidic is stronger on rainy daysthan on haze days and weakest on sandstorm days. The fitting slope of cation-anion is only0.24,demonstrating alkaline characteristics. Ca²⁺ plays an important role in the neutralization ofHNO₃, and H₂SO₄. The correlation coefficient of NO₃^-and SO₄^2- is better on rainy days than thatbefore and after sandstorm. The fitting slope on haze days and clear day is0.97and0.86,respectively, indicating that the positive and negative ions are basically in balance. Thedeteriorated motor vehicle emissions lead to a more important role of NO₃^-in aerosols byaccelerating the formation of haze.