Morphological Distribution Characteristics And Health Risk Assessment Of Heavy Metals In PM_2.5 In The Northern Suburb Of Nanjing

Currently,the air pollution of fine particulate matters(PM_2.5)is becoming increasingly globally,which is a common environmental issue for all mankind.Because it is easy to enrich harmful substances such as heavy metals and seriously threatens human health,it has attracted wide attention at home and abroad.To understanding the pollution of heavy metals in atmospheric PM_2.5 in the northern suburb of Nanjing and it's health risks to the local crowd,setuping sampling points in the northern suburb of Nanjing and monitoring them for a long time,improved stepwise chemical extraction method?BCR?is used to analyzed the daily mean concentration,characteristics of occurrence forms and bio-availability of 13 heavy metals elements,including Al,V,Cr,Mn,Co,Ni,Cu,As,Se,Sr,Cd,Ba and Pb,with 4 occurrence forms?water-soluble forms F1?reducible forms F2,oxidizable forms F3,residual forms F4?in PM_2.5,and the sources of heavy metals in PM_2.5 were analyzed by using enrichment factor method and principal component analysis;Under the framework of the health risk assessment model proposed by the American Academy of Sciences,combining with Fourier transform and frequency-domain filtering method,the method of Long Short-Term Memory Neural Network?LSTM-NN,one of deep learning methods?is used to analyzed the change trend of 5 heavy metal elements with biologic available form over time,and a more reasonable and scientific assessment of the health risk of heavy metals in PM_2.5 is proposed by improving the method of value of relevant parameters.Main conclusions indicated that:?1?During the sampling period,the total concentration of heavy metals in the PM_2.5,from high to low,are Al,V,Cr,Mn,Co,Cu,Sr,Cd,Ba,Pb,Ni,As and Se in the northern suburb of Nanjing respectively.?2?There are differences in the occurrence forms distribution of 13 heavy metals:Al exists mainly in F4 and F2 forms;V,As,Sr mainly exist in F1 form;Cr distribution of four occurrence forms is more average;Mn and Se mainly exist in bio-available forms;Co,Cu and Pb mainly exist in F1 and F2 forms;Ni mainly exist in F3,F4 and F2 forms;Cd and Ba,exist in F1 form,and the other forms are more average.Among the main sources of heavy metals in PM_2.5 in the northern suburbs of Nanjing are?1?metal smelting,?2?fossil fuel combustion,?3?industrial processes,?4?dust raising and?5?other unknown or natural sources,with contribution rates of 49.0%,18.7%,10.9%,7.00%and 14.4%,respectively.The sequence of 13heavy metals is Sr,Mn,Se,Pb,V,Cu,Co,Ba,Cd,As,Cr,Ni,Al in order of bio-availability from high to low.?3?The change trend of the bio-available form concentration heavy metal in PM_2.5 was analysised using LSTM neural network,which obtained the well result,revealed the five heavy metal bio-available form concentration change trend:The decline of Al is slow;while the concentration of Ba?Pb?V three heavy metal elements decreases significantly;and Mn increases slow.?4?The non-carcinogenic risk of 10 heavy metals in PM_2.5 was Mn,Cd,Cr,Pb,Co,As,Cu,V,Ba,Ni from high to low,which Mn non-carcinogenic risk is highest and their bio-available form concentrations are slowly increasing.The four carcinogenic heavy metals are Cr,As,Cd,Ni from high to low.