The Impact Of Chemical Components Of Fine Particulate Matter On Regional Visibility Impairment And The Source Apportionment

The haze problem is one of focuses of air quality problems in the Pearl River Delta Region?PRDR?.Haze can cause visibility degradation and it also has potential health effect on human being.Therefore,it attracts much attention from researchers as well as the public.In thhis study,we investigated the relationship between concentrations of PM_2.5 and its major chemical components and visibility data at Tianhu,a regional site in PRDR.The influence of PM_2.5,themajor chemical components and meteorological parameters were analyzed.The IMPROVE formula was used to reconstruct the light extinction coefficients?bext?and the applicability of the IMPROVE formula was evaluated.By using PMF model,we obtained the major source factors of PM_2.5 and visibility degradation.The results of this study may give some clues to develop more scientific and effective pollution control measures.?1?The results suggest that aerosol pollution is more likely occur in autumn and winter.Nss-SO₄^2-is the predominant contributor to PM_2.5,contributing 27.2%,followed by OM and NH₄⁺,while the contribution by NO₃^-is relatively low,only accounting for 4.4%.?2?Statistical analysis on PM_2.5 and its chemical composition,meteorological parameters,and visibility shows that meteorological conditions have substantial effects on visibility,positively through diffusion and wet scavenging and negatively by high relative humidity.The net effect causes highest visibility in summer when PM_2.5 concentration is relatively small,while lowest visibility in spring although PM_2.5 concentration is lowest.PM_2.5 has been shown to have more contribution on the degradation of visibility in autumn and winter.The concentrations of PM_2.5 and its chemical composition are higher in haze days?visibility less than 10 km when excluding natural visibility-degrading phenomena?than in non-haze days?visibility ? 10 km?,especially for NO₃^-.From the significant correlations between visibility and nss-SO₄^2-,NH₄⁺,OM,it can seem that secondary aerosol have important effect on visibility impairment.?3?By comparing the fitness of calculated and measured bext respectively with original and revised algorithm,it shows that the revised algorithm is more reliable to evalue the average light extinction over one period with a slope close to 1,although the determination coefficient?R2?with original algorithm is better.The relationship between reconstructed bext and measured bext was investigated under the influence of seasonality,visibility and PM_2.5 concentration.We found that bext could be successfully reconstructed using revised IMPROVE formula in high PM_2.5 days,while the performance of the formula was unsatisfactory for bext reconstruction in low PM_2.5 days.Result of correlation analysis shows that in low PM_2.5 days,meteorological conditions have stronger impacts on visibility than PM_2.5.When PM_2.5 concentrations are high enough,PM_2.5 plays significant role in visibility impairment.The threshold value is 57.6 ?g m-3 by comparing the performance under different PM_2.5 concentration range in this study.?4?The 6 contribution factors obtained by PMF model are as follows: the largest contributor of industry accounting for 27.2%,followed by heavy oil combustion?25.4%?,secondary nitrate?15.3%?,biomass burning?8.7%?,vehicle?14.2%?,crustal dust?9.2%?.By comparing the results of three different methods of calculating factor contributions to light extinction,it shows that heavy oil combustion,secondary nitrate and industry factors make largest contribution,followed by coal combustion factor.The contribution of biomass burning factor is relatively small,and crustal dust factor is nearly negligible.