Study On Particle Size Distribution Characteristics, New Particle Generation And Chemical Composition Of Atmospheric Aerosols In Ningbo Coastal Area

The coastal areas in China,including i.e.,the Yangtze River Delta,Pearl River Delta,are densely-populated,concentrated manufacturing industry,thus the atmospheric particle pollution was so serious.The coastal areas are affected by the continental-and marine-air masses.Severe eutrophication,algae farming in the coastal waters of China and the heterogeneous reactions on the seawater surface,all of them could produce a large number of volatile compounds and may be an important source of new particle formation.Under the circumstance of atmospheric combined pollution,studying the atmospheric size distribution,new particle formation and its chemical composition at the coastal site of eastern China,which is important for classify PM control strategy of Chinese coastal regions.This study presented the formation and dissipation process of particulate matter（PM）pollution in winter at a coastal industrial park in Ningbo city,China.The sampling period included prior to the heavy pollution period,the heavy pollution period,the new particle formation period and the Chinese New Year holiday period.Positive matrix factorization（PMF）analysis identified three PNSD factors and three organic aerosol（OA）factors.Contributions and potential source regions of these factors were investigated for four typical periods.Results show that the relative contributions from aged 250 nm-factor,fresh 35 nm-and 80 nm-factors were strongly affected by local fresh emissions and regional new particle formation.The contributions of NO₃^-and SO₄^2-to non-refractory submicron particulate matter were largely dictated by whether the air mass trajectory went over the sea or the continent.NO₃^-was abundant（up to 44%of NR-PM₁）in cold and dry continental air masses,while SO₄^2-formation（up to 39%of NR-PM₁）was preferred in humid and warm marine air masses.The more-oxidized oxygenated OA（MO-OOA）was the most abundant OA factor（44-66%of total OA）throughout the entire field campaign,while an enhanced contribution of 39%from hydrocarbon-like OA（HOA）was observed prior to heavy pollution period.On average,secondary components SO₄^2-,NO₃^-,NH₄⁺,MO-OOA and less-oxidized oxygenated OA（LO-OOA）contributed 90±7%of NR-PM₁,while primary components HOA and Cl^-only accounted for the remaining 10±7%.The study analyzed the particle number size distribution and NPF event measurements at the coastal industrial park of Ningbo city,China from the year of 2018 to 2019.The highest nucleation-mode particle number concentration(daytime maximum～4.9×10³ cm^-3 in average)and NPF frequency（8%of the observation days）were observed in the continental-marine air masses that originated from North China Plain and traveled along the coastline before arriving at the coastal site.The nucleation rates（J₂）at this coastal site are similar to those reported in the urban environments around the world,probably due to the influence of local industrial emission.Ion to total particle number concentration ratios in 2-7 nm and 7-20 nm were 1.5%and 12%,respectively,during the NPF periods.Neutral new particle formation pathway thus dominated over ion-mediated pathway at this coastal site.Our observation also showed that number concentration and formation rate of neutral new particles decreased monotonically with particle size in the size range of 2-25 nm,while those of newions increased with particle size.Such difference points to the mechanisms of ion-aerosol attachment and ion-ion recombination in the atmosphere.The behavior of appearance time-based growth rates,however,are similar for neutral particles and ions,which was attributed to the fact that the formation of ions over 2 nm was largely controlled by the attachment of air ions smaller than2 nm to larger neutral particles.Meanwhile,intense new particle formation（NPF）events were continuously observed in the mesolittoral zone during algae growth and farming season at Xiangshan gulf of the east China coast.High particle iodine concentrations during the NPF period were measured by soot particle aerosol mass spectrometry（SP-AMS）and ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry（UPLC/QTOF-MS）,5 inorganic iodine species and 45 organic iodine compounds were identified,confirmed that the NPF events were induced by iodine species.The concentrations and size distributions of iodine species were measured during the iodine-induced NPF,continental NPF,and non-NPF days at the coastal site.We found that the iodide compounds（except iodoacetic acid）have a nucleation mode distribution between 22 nm and 35 nm during the iodine-induced NPF events.However,the iodine concentration was relatively low in the continental NPF and non-NPF days.During the iodine-induced NPF events,the total iodine concentrations was 3.1 times as the continental NPF days.The most prominent iodine was IO₃^-,its molar concentration accounted for 42.5%of the total iodine.The HSO₄^-was detected in the iodine nucleation mode particles,indicating that sulfuric acid may play an important role in the iodide nucleation process.The iodine of continental NPF days is mainly distributed in the Accumulation mode between 500 and 700 nm,indicating that iodine could not be the nucleation composition in this NPF events.Our study provides important information on iodine speciation,size distributions,and its role in NPF in the context of heavy air pollution in China’s coastal areas.The new particle formation events are induced by iodine nucleation at Xiangshan gulf of east China,but the organic compounds accounts for most of its mass concentration,we investigated size-dependent molecular characteristics of coastal organic aerosols from<0.032to 3.2μm,proving the organic compounds plays important role during the growth of ultrafine particles.The Fourier transform ion cyclotron resonance mass spectrometry（FT-ICR-MS）was used to measure the different organic compounds（CHO,CHON,CHOS,CHONS,I-OC and Cl-OC）.The number of coastal organic molecules in different particle sizes showed a bimodal pattern,with one peak in<56 nm and other peak in 0.32-0.56μm.CHON has the highest signal intensity in ultrafine particles（<100 nm）,accounting for 55%and 80%of the organic molecules number in the ESI-and ESI+modes,respectively.The proportion of CHON decreased with particle size.CHO is the second largest contributor of the organic compounds in coastal ultrafine particles,which proportion increased with particle size.Strong connection between C_20-33H_hO_oand C_18,30H_hO_oN_n compounds in particles smaller than 0.10μm and the volatile organic compounds（Solid Phase Micro-Extraction-GC-MS analysis）emitted from local intertidal macroalgae suggests that the organic compounds（OC）in ultrafine particles are formed probably via the gas-phase oxidation of long-chain fatty aldehydes or acids during the coastal NPF events.CHN and I/Cl/Br-containing OC account altogether for only 4%of OC formulas.