Occurrence of Low Molecular Weight Organic Acids in the Aerosol Shui-Ping Wu, Meng-Meng Zhang, Xin-Hong Wang State key Laboratory of Marine Environmental Science Xiamen University http://mel.xmu.edu.cn Email: wsp@xmu.edu.cn
Content 1. Why do we study the organic acid? 2. How to measure the organic acid? 3. Size distribution, diurnal difference, inventory source of organic acid 4. Source identification 5. Conclusion
Why? Organic acid (fatty acid, dicarboxylic acid and aromatic acid) Effects on ambient environment Relationship between organic acids and haze
Organic Acid Fatty acid Stearic acid (C16),Palmitic acid (C18) Dicarboxylic acids C 2 -C 10 : oxalic,malonic,succinic,glutaric, adipic,pimelic,suberic,azelaic,sebacic The secret of memory : Oh my, such great apple pie! Sweet as sugar Aromatic acids phthalic,isophthalic,tetrephthalic
Effects on ambient environment Very likely to condense onto aerosol due to their low vapor pressure. Be much hygroscopic and have potential effects in direct cloud formation acting as cloud condensation nuclei (CCN), can reduce surface tension of CCN and affects cloud formation. Total dicarboxylic acids account for about 1 3% of the total particulate carbon in the urban areas and even above 10% in the remote marine environment, can contribute to the acidity of local acid rain. Sources of haze.
Source of dicarboxylic acids in airborne particulate matter Anthropogenic source Photochemical reaction of fossil fuel, waste gas, automobile exhaust. Biogenic emissions Oxidation and degradation of Monoterpene, Isoprene, Methyl butene diol emitted from trees and unsaturated fatty acids from ocean. Size distribution Size distribution and diurnal and nocturnal Variations data are useful in understanding the formation pathways and potential contributions to CCN.
How? Sample collection TSP sampler (high flow rate, Tianhong ),12-stage Micro-Orifice Uniform Deposit Impactor (MOUDI) (MSP-100) Teflon and quartz filter(φ47mm) ;glass filter(8 10inch) filter was cut into pieces, ultrasonically extracted with 25 ml 3 methanol for 15 min; further concentrated to almost completely dried by rotary evaporation. Derivative reaction 14% BF 3 /methanol mixture (0.3 ml) 100 reacted for 30 min. GC/MS analysis extracted with 5ml of n-hexane after adding pure water (3 ml) and acetonitrile (0.3 ml). The n-hexane layer was further washed with pure water(3ml) and concentrated to 1mL using high pure N 2.
Sampling site N Xiamen City Jinmen City the Ocean Building Taiwan Strait
Range of particle size for MOUDI Level Size(um) Level Size(um) S1 >18 S7 0.56-1.0 S2 10-18 S8 0.32-0.56 S3 5.6-10 S9 0.18-0.32 S4 3.2-5.6 S10 0.1-0.18 S5 1.8-3.2 S11 0.056-0.1 S6 1.0-1.8 S12 <0.056
Size distributions Particle size distributions. Size distribution of organic acid associated with particle. Organic distribute between coarse and fine particle.
Size distributions of particle 0.70 0.60 paticle 0.50 dc/cdlogdp/m 3 0.30 0.10 0.01 0.1 1 10 100 Core mode <0.1µ m Accumulation mode (0.1-2µ m) Coarse mode >2 µ m
Size distributions of organic acids-1 1.20 1.20 1.00 di-c2 1.00 di-c4 0.80 0.80 dc/cdlogdp/ug/m 3 0.60 dc/cdlogdp/ug/m 3 0.60 0.01 0.1 1 10 100 0.01 0.1 1 10 100 1.20 1.00 di-c5 0.80 0.70 di-c7 0.60 dc/cdlogdp/ug/m 3 0.80 0.60 dc/cdlogdp/ug/m 3 0.50 0.30 0.10 0.01 0.1 1 10 100 0.01 0.1 1 10 100
Size distributions of organic acids-2 0.60 0.50 di-c6 1.20 1.00 di-c3 dc/cdlogdp/ug/m 3 0.30 0.10 dc/cdlogdp/ug/m 3 0.80 0.60 0.01 0.1 1 10 100 0.01 0.1 1 10 100 dc/cdlogdp/ug/m 3 1.00 0.90 0.80 0.70 0.60 0.50 0.30 0.10 di-c8 dc/cdlogdp/ug/m 3 1.20 1.00 0.80 0.60 di-c9 0.01 0.1 1 10 100 0.01 0.1 1 10 100
Size distributions of organic acids-3 dc/cdlogdp/ug/m 3 0.45 0.35 0.30 0.25 0.15 0.10 0.05 di-c10 0.01 0.1 1 10 100 dc/cdlogdp/ug/m 3 0.90 0.80 0.70 0.60 0.50 0.30 0.10 Phthalic acid 0.01 0.1 1 10 100
Size distributions of organic acids-4 1.20 1.00 C16 fatty acid 0.90 0.80 0.70 C18 fatty acid dc/cdlogdp/ug/m 3 0.80 0.60 0.01 0.1 1 10 100 dc/cdlogdp/ug/m 3 0.60 0.50 0.30 0.10 0.01 0.1 1 10 100
Size distribution of C3/C4 5 4 Ratio of C3/C4 3 2 1 0 <0.056 0.1-0.18 0.32-0.56 1.0-1.8 3.2-5.6 10-18 0.056-0.1 0.18-0.32 0.56-1.0 1.8-3.2 5.6-10 Aerosol size (um) >18
20 Size distribution of C6/C9 16 Ratio of C6/C9 12 8 4 0 <0.056 0.1-0.18 0.32-0.56 1.0-1.8 3.2-5.6 10-18 0.056-0.1 0.18-0.32 0.56-1.0 1.8-3.2 5.6-10 Aerosol size (um) >18
Correlation between PM and organic acid C2 C3 C4 C5 C6 C7 P a rtic le 0. 72 0. 75 0. 87 0. 83 0. 90 0. 74 C8 C9 C10 P h C16 C18 P a rtic le 0. 71 0. 69 0. 31 0. 74 0. 63 0. 49 High correlation coefficient shows the carboxylic acids and PM have the same sources
Source inventory of dicarboxylic acids 100% 90% dic6: about 90% dic10:about 10% 80% 70% 60% 50% 40% 30% 20% 10% C10 C9 C8 C7 C6 C5 C4 C3 C2 0% beef pork chicken engine wood wood soot dic2,dic3 abundant sources dic2>75%,dic3<1%
变化趋势 Trend Aging process of organic acid in engine exhaust Espousing outdoor for 96h and sample every 12h Analyze the relative content of each component. c2 c3 c4 c5 c6 c7 c8 c9 c10 Ph c16 c18 R2 0. 67 0. 80 0. 87 0. 87 0. 58 0. 63 0. 75 0. 04 0. 66 0. 86 0. 11 0. 07 C6 C10 is attributed to the direct of vehicle exhaust, and can degrade into dic2-c5 and dic7-c8 in ambient air. The relative of Ph increased due to the new formation through reaction of benzene/toluene and OH/NOx radical. dic9, dic16 and dic18 mainly from biogenic source.
Diurnal difference of organic acid 1000 Day Night 100 Conc ng/m 3 10 1 0.1 di-c2 di-c3 di-c4 di-c5 di-c6 di-c7 di-c8 di-c9 di-c10 C16 C18 Ph
Source identification Ratios 20 18 16 14 12 10 8 6 4 2 0 > > > C2/C4 (D) C2/C4 (N) C3/C4 (D) C3/C4 (N) C6/C9 (D) C6/C9 (N)
Conclusion Different organic acids show different size distribution modal (bimodal for dic2-dic9,c16 and C18, multimodal for dic10, monomodal for Ph). Clear diurnal difference (day>night for dic2-dic8, dic10, Ph indicating vehicle direct emission or photochemical reaction; night>day for dic9, C16 and C18 suggesting biogenic source, such as plant, sea salt). Aging process indicate dic6 and dic10 can be degraded into dic2-dic5 and dic7-dic8, respectively.
Acknowledgement This Work was supported by National Natural Science Foundation of China.
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