Geochemical Study Of Personal Exposed PM_2.5 In Typical Cities

The process of urbanization and industrialization has led to a surge in atmospheric particulate matter,which is a major threat to global public health.Ambient fine particulate matter(PM2.5)costs more than four million deaths in 2017,ranking sixth in the Global Burden of Disease.Present epidemiological studies on air pollution commonly use fixed-site measurements to estimate personal exposure levels.Considering influence from time-activity parten of each individual,personal monitoring is the gold method to estimate personal exposure.With the widespread use of personal monitors,baseline drift is still a problem in real-time monitoring data.Real-time data mining also needs further exploration.PM2.5 in both indoor and outdoor microenvironments(MEs)impact personal exposure while existing researches about personal exposure in MEs were mostly conducted when ambient PM2.5 concentrations were pretty low.It is important to characterize personal exposure under various ambient PM2.5 levels as well as to determine influence from indoor and outdoor particles.Air pollution is a major concern in China.Nanjing,the second largest city in Yangtze River Delta,has the most haze days among all provincial capitals in China in 2012.In comparison,New York City(NYC)is one of the few cities where annual PM2.5 concentrations meet WHO guidance(<10?g/m3).Based on comprehensive assessment and calibration of a prevalent real-time PM2 5 monitoring instrument,we conducted a series of studies in Nanjing and NYC.Personal exposed PM2.5 and black carbon(BC)were measured in multiple non-residential MEs under hazy and non-hazy days.With application of X-ray Fluorescence,Fourier-transform Infrared Spectroscopy,Scanning Electron Microscopy tests and Mass Reconstruction,we compared the influence from indoor/outdoor PM2.5 and personal activities on the concentrations and components of personal exposed PM2.5.Health risk of PM2.5 was estimated based on its trace element components.A peak analysis method was then developed to quantify personal PM2.5 exposure to indoor secondhand smoke(SHS).Based on these studies,we found out that:(1)The established running baseline and gravimetric calibration method(RBGC)successfully corrected baseline shift issue in real-time PM2.5 data.Baseline shift problems dropped from 48%for raw data to<10%after application of RBGC.(2)With the ratio of personal exposure to ambient PM2.5 levels(rp/a)around 1.70±1.94,personal exposed PM2.5 levels in most MEs were higher than the ambient levels in non-hazy days.The ratio(0.85±0.31)was lower and less variable in hazy days.Personal exposed PM2.5 level in MEs with point source(e.g.street food vendor)could be 3 times or more higher than the ambient in non-hazy days,and 12?17%than the ambient in hazy days.In MEs with good air filtration,personal PM2.5 exposure can be as low as 0.(3)Average BC exposure for people in Nanjing was 16.6?g/m3 in hazy days,3.2 and 11.1 times of that in non-hazy days in Nanj ing and NYC.The ratio of personal exposed BC to PM2.5 was barely influenced by transport MEs in Nanjing.In comparison,this ratio could reach 20%in NYC,more than 3 times of daily average.(4)Among multiple commuting methods,cycling contributed the highest particle exposure dose in Nanjing.The extra exposure from one-hour riding in hazy days was equivalent to an increase of 1.4?g/m3 in BC and 26.4?g/m3 of PM2.5 in ambient air.While in NYC,the highest BC and PM exposure dose was from underground metro station,which were 2.1 and 1.3 times of those when cycling.Impact on the exposure from high level of PM2.5 emission could overwhelm that from personal activity.(5)In personal exposed PM2.5,soil and sea salt contributed 2?17%in non-hazy days and decrease to 3?13%in hazy days.Heavy metals in personal exposed PM2.5 was 0.003?1.6?g/m3 in non-hazy days,about half the concentration of that in hazy days.When using BC to estimate change of anthropogenic source,secondary PM2.5 in personal exposed particle accounted for at least 40%.(6)In both non-hazy and hazy days,ambient PM2.5 explained 34%and 64%of the variability of personal PM2.5 components in Nanjing.While in NYC,ambient and residential PM2.5 explained 67%and 37%of personal PM components respectively.(7)Based on peak analysis of real-time PM2.5 data for NYC children,average SHS exposure duration accounted for 5%of total exposure time,but represented 13%of total PM2.5 exposure.Peak area for those from smoke families was 297?g/m3*hour,6 times of those from non-smoke families.In comparison,PM2.5 mass concentration for SHS exposed children was only 1.6 times of the unexposed ones.(8)In Nanjing,potential health risk from heavy metals was mainly from inhalation exposure.Via inhalation,the non-carcinogenic and carcinogenic risks from PM2.5 were 4.5 and 500 times of the safe limits.Among all heavy metal,Cr and Pb contributed the highest carcinogenic risks,the Incremental Lifetime Cancer Risk for Cr and Pb were 32 and 393 respectively.In NYC,the main risk was from ingestion exposure,non-carcinogenic and carcinogenic risks of which were 2.2 and 2.0 times of the safe limits.