Top PDF Sources and composition of urban aerosol particles

Carlo, P. F., Salcedo, D., Onasch, T., Jayne, J. T., Miyoshi, T., Shimono, A., Hatakeyama, S., Takegawa, N., Kondo, Y., Schneider, J., Drewnick, F., Borrmann, S., Weimer, S., Demerjian, K., Williams, P., Bower, K., Bahreini, R., Cottrell, L., Griffin, R. J., Rautiainen, J., Sun, J. Y., Zhang, Y. M., and Worsnop, D. R.: Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically-influenced Northern Hemisphere midlatitudes, Geophys. Res.

nation of thermal vaporization (∼ 600 ◦ C) under high vacuum (∼ 10 −8 torr), electron im- pact ionization (70 eV) of vaporized molecules, and mass spectrometric analysis of the resulting ions (Jayne et al., 2000). AMS can also provide information on the size distri- butions of species via a combination of aerodynamic lens, chopper, and Particle Time- of-Flight (PToF) detection. Five aerosol species in NR-PM 1 , i.e., sulfate, nitrate, ammo-

from photochemical oxidation of organic gases (Agarwal et al., 2010; Ram and Sarin, 2010; Salma et al., 2007; Wang et al., 2012a; Yu et al., 2004, 2005). Moreover, biomass burning is also an important source of WSOC. Thus a ma- jor peak in the fine mode was found in Xi’an during the non-dust storm period (Fig. 9a). The small peak of coarse mode of WSOC can be explained by a nature source such as pollen and soil (Fig. 9a), because water-soluble organic compounds like glucose (Graham et al., 2002; Wang et al., 2006b, 2009, 2011a, b) and humic acid (Brooks et al., 2004; Dinar et al., 2006; Havers et al., 1998) are enriched in these sources, in addition to deposition of anthropogenic pollu- tants onto dust. During the dust storm period WSOC still displayed a bimodal pattern, but the fine mode significantly decreased while the coarse mode sharply increased as a dom- inant peak. Our previous study (Wang et al., 2012b) found that during the DS II period secondary organic aerosols in the Mt. Hua air were mostly formed from the local sources rather than being transported from the upwind region, and are of a size within the fine mode. However, during the event primary organic aerosols such as water-soluble organic com- pounds, such as glucose and trehalose and water-insoluble organic compounds like high molecular weight (HMW) n- alkanes, fatty acids and fatty alcohols, were mostly derived from biota, e.g. pollen, spore, invertebrate animals and plants in Gobi desert (Wang et al., 2012b). Those Gobi dust de- rived organic aerosols are of larger sizes and dominated in the downwind atmosphere in the event, resulting in a sharp increase in OC in the atmospheres of Mt. Hua and Mt. Tai in comparison to those in the nonevent (Wang et al., 2011c;

ral variations are illustrated in Fig. 3. It should be noted that an empirical OC/POM conversion probably leads to an over- estimation of POM besides the errors in measurements and water content calculation. As a result, mass of the Residual in 10 of the 123 samples were calculated to small negatives. To avoid this matter affecting further calculation in the Mie Model, these negative values were assigned to zero. As il- lustrated in Fig. 3, of the total mass, inorganic species, wa- ter, POM, EC and the Residual accounted for 42–51 %, 10– 15 %, 17–23 %, 8–9 % and 10–22 %, respectively. Moreover, (NH 4 ) 2 SO 4 , Na 2 SO 4 , K 2 SO 4 and HNO 3 are the major inor-

volatile. High hygroscopicity is specific to sea environments only. The effect of me- teorology on the particle hygroscopicity is small, though HGF values in moist and re- cently marine air masses are generally lower. The aerosol particle hygroscopic growth factors are enhanced in polar, continental air masses mainly for two reasons: 1) Het- erogeneous aging of marine originated organic aerosol increases and 2) MSA volume

New particle formation events were detected on 21% of the classified days. A typical feature of the events is the preference of negative ions in the initial phase of the parti- cle formation. One event day was analyser further and ion and total particle formation rates were calculated. The to- tal 2 nm particle formation rate was 1.3±0.1 cm −3 s −1 and the maximum contribution from ion-mediated particle for- mation on that day was around 30%. Growth of <1.5 nm ions, as a first phase of new particle formation, was observed at the measurement site on 21 January. Direct detection of the growth of the smallest cluster ions indicates that nucle- ation in Antarctica can occur in the boundary layer and/or in the lower troposphere. In air masses of freshly nucle- ated particles the HGF values are decreased but will increase with time in subsequent particle growth. Thus, aging of the aerosol seems to increase the particle hygroscopicity. The variation of HGF values during new particle formation and growth can be explained by two factors: 1) increased organic aerosol contribution in the initial phase of particle formation and further organic aerosol heterogeneous oxidation and con- densation, and 2) decreasing organic contribution in compar- ison to other condensing vapours following the growth of the nucleation mode. However, both cases suggest that organics, or other less hygroscopic species, participate in the particle growth process.

categories. Here the total organic signal frames the aver- age mass fractions of each of the OA components (OOA I, OOA II, HOA, WBOA) as well as the residuum in the green pie. The fractional contribution of the four components dif- fers dependent on the air mass category. Nevertheless, low- volatile OOA I can be found in each air mass type as the major submicron aerosol fraction besides all marine influ- enced air masses where sulfate plays the most important role (Sect. 3.3). Referred to the OA fraction OOA I is approx- imately in the same order (35 % in “Portugal + Marine” up to 49 % in “Continental”) in all air mass categories. The less aged OOA II component appears as second most abun- dant fraction of the OA in all air mass types with a contri- bution of approximately 25 % beside the “Marine” category that has a lower OOA II fraction of 13 %. Over marine envi- ronments particle aging is a characteristic feature (Topping et al., 2004), resulting in a more oxygenated and a less volatile aerosol. In contrast, in continentally influenced air masses typically freshly produced biogenic and anthropogenic or- ganic material exists, resulting in OOA II aerosol after photo- chemical processing. HOA concentrations are expected to be most prominent downwind of the urban city Huelva, however HOA aerosol undergoes rapid losses due to oxidation while it is transported (Zhang et al., 2007). Like in the studies of Zhang et al. (2007), we also found OOA concentrations sim- ilar or even enriched when the air was transported downwind of urban areas, likely due to condensation of vapors onto the pre-existing particles and oxidation of HOA, respectively. In contrast to all other air mass types, the “Marine” cate- gory contained HOA as the second most abundant organic aerosol component (25 % of total OA) potentially originating from shipping emissions. In “Portugal + Huelva” air masses WBOA levels are more prominent and exceed HOA which is likewise the case for the city Zurich (Lanz et al., 2008). Due to the beginning of the winter season in the south of Spain with cooler temperatures and rain, domestic heating is an im- portant contributor to this aerosol type as people heat using wood. This becomes apparent in increased WBOA concen- trations especially in the evenings. In addition, as the mea- surement site is surrounded by pines and eucalyptus forests with agricultural activity WBOA average values around 7 %

Average concentration of IEPOX-OA at JST and LRK in- creased during summer. At LRK, the average concentration of IEPOX-OA reached a maximum in summer, but its relative contribution to total OA mass was lower due to the increas- ing concentration of 91Fac. Concentrations of IEPOX-OA at both sites are comparable (Fig. 8), suggesting that in summer this factor may become spatially homogeneous in the south- eastern US. Since measurements at JST and LRK were con- ducted during different years, meteorological changes might play a role in site-to-site comparison. At LRK, IEPOX-OA showed a small increase around noon, while at JST there was a local maximum in the mid-afternoon, suggesting an influx of IEPOX-OA likely transported from surrounding forested areas. The time series of IEPOX-OA was moderately cor- related with nitrate (r 2 ∼ 0.4) at JST, and at LRK, stronger

pogenic origin, consisting of both primary and secondary particles from a variety of sources (e.g., Seinfeld and Pandis, 1998). Its chemical and elemental composition, optical, hygroscopic and other important physical and chemical properties vary both spatially and temporally. Additionally, there is variation of all these quantities over parti- cle size. The assessment of climatic and adverse health effects of atmospheric aerosol

Carlo, P. F., Jayne, J. T., Mortimer, P., Worsnop, D. R., Kolb, C. E., Johnson, K. S., Zuberi, B., Marr, L. C., Volkamer, R., Molina, L. T., Molina, M. J., Cardenas, B., Bernabe, R. M., Marquez, C., Gaffney, J. S., Marley, N. A., Laskin, A., Shutthanandan, V., Xie, Y., Brune, W., Lesher, R., Shirley, T., and Jimenez, J. L.: Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with Aerosol Mass Spectrometry: results from the

comparison indicated the model was able to reproduce the measurements, we cannot conclusively state that the model managed to reproduce the aerosol chemical composition be- cause no measurement information on the exact aerosol com- position was available. However, given our efforts to accu- rately take into consideration the partitioning of emissions (including various VOCs) as well as the use of one of the most accurate aerosol–chemistry reaction schemes available at the present time (VBS scheme), the good match between the total aerosol mass concentrations modeled and observed yields some confidence in these results. We now turn our fo- cus on the composition of aerosol particles at the biomass burning emission location, along the plume, and in Singa- pore. Figure 5 shows the horizontal cross section of primary aerosol mass concentration on the left and SOA mass concen- tration on the right, at the surface level on 3 October 2006 at 12:00 LT (local time). Although being a snapshot, it is a rep- resentative one involving the interaction between remotely emitted biomass burning aerosols and freshly emitted urban aerosols in Singapore.

particles, is toxic to forests (Harrison et al., 2005) and rec- ognized as an important biomass burning SOA molecular marker (Iinuma et al., 2010). An OH exposure equivalent to only a few days of atmospheric exposure leads to an or- der of magnitude enhancement in MNC hygroscopicity. This implies that aged MNC is more susceptible to wet deposi- tional losses over atmospherically relevant particle transport timescales, e.g., through cloud formation, compared to fresh MNC. Calculations from Petters et al. (2006) indicate that substantial wet depositional losses can occur when κ > 0.01. The question of the utility of MNC as a molecular marker for source apportionment is raised since molecular markers are assumed to be inert over the course of its lifetime in the atmo- sphere. Clearly, OH oxidation of MNC influences its chem- ical composition, but in doing so also decreases its atmo- spheric lifetime by enhancing its CCN activity. However, our results strongly suggest that if the OA is WSOC-dominated, e.g., by LEV, the reaction products likely have similar CCN activity to the parent WSOC, and thus particle oxidation plays a very minor role in enhancing the CCN activity of WSOC. Indeed, only a minor enhancement in the hygroscop- icity of BBA, produced from controlled wood burning, was observed after several hours of photo-oxidation, likely a re- sult of significant BBA WSOC content (Martin et al., 2013). Much less is known of the effects of chemical aging on the CCN activity of internally mixed water-soluble and insoluble organic–inorganic particles. While oxidative aging can en- hance the hygroscopicity of single-component particles with initially low water solubility, atmospheric aerosol particles are not often pure and consist of both organic and inorganic compounds (Laskin et al., 2012; Knopf et al., 2014; Mur- phy and Thomson, 1997; Murphy et al., 2006; Middlebrook et al., 1998). Organic compounds alone can influence the hy- groscopicity of inorganic aerosol

Chow, J. C., Watson, J. G., Chen, L. W., Chang, M. C., Robinson, N. F., Trimble, D., and Kohl, S.: The IMPROVE A temperature protocol for thermal/optical carbon analysis: maintaining consistency with a long-term database, J. Air Waste Manage., 57, 1014–1023, 2007. Deng, X. J., Tie, X. X., Zhou, X. J., Wu, D., Zhong, L. J., Tan, H. B., Li, F., Huang, X. Y.,

3. The minimum temporal coverage for the trend estimate is a continuous 5-year set of the complete yearly data. Figure 3 shows the Taylor diagram, which describes three statistical metrics in one plot, viz. temporal correlation, nor- malized standard deviation, and normalized centered root- mean-square (rms) difference of the two data sets (Taylor, 2001; Solomon et al., 2007; Meehl et al., 2007). The monthly AERONET AOTs are resampled at the local equatorial cross- ing times of the instruments for the temporal pattern correla- tion analysis. The AERONET stations used in Fig. 3 are clas- sified by their regional dominant aerosol types (e.g., indus- trial/biomass burning, free troposphere, desert dust, and rural aerosols) and are listed in Table 2. The aerosol classification is explained in Yoon et al. (2012). At the stations influenced by desert and rural aerosols, the temporal pattern correlation is obtained for all the sampling times i.e. 0.91 ≤ temporal R ≤ 0.98, 0.87 ≤ normalized temporal STD ≤ 1.13, and 0.19 ≤ normalized centered rms difference ≤ 0.44. In con- trast, the correlation at the stations where industrial/biomass burning and free tropospheric aerosols are dominant is poorer (0.72 ≤ temporal R ≤ 0.94, 0.78 ≤ normalized tempo- ral STD ≤ 1.21, and 0.36 ≤ normalized centered rms differ- ence ≤ 0.80). As there is no difference in retrieval accuracy, cloud-filtering method, and spatial resolution, as previously mentioned, this difference can be only attributed to the dif- ferent and limited sampling times and it can relate to diurnal variation of the aerosol sources (Smirnov et al., 2002; Kocha et al., 2013; Arola et al., 2013). In particular, the temporal correlation coefficient at the Beijing station ranges from 0.72 to 0.83, and there is good chance of deriving different trends from the different/limited samplings over such a large urban agglomeration.

Rogge et al. (1991) explained the formation of PM from (meat) cooking activities by nu- cleation and growth of evaporated grease, which most likely yields spherical particles. For periods when BBOA dominates the organic composition, also ammonium nitrate concentrations are rather high. As shown in Fig. 4, BBOA is slightly increased during nighttime, when lower temperatures favor partitioning of semi-volatile species such as

The issue of the impact of optically active particulate mat- ter on the local energy budget in the Himalaya has been put forward by recent observations showing that pollution aerosol from India and Pakistan can be transported by moun- tain breezes up to the high altitude (Carrico et al., 2003; Ramanathan et al., 2007; Bonasoni et al., 2008; Venzac et al., 2008; Komppula et al., 2009). Measurements of aerosol chemical composition and aerosol optical depth in the Nepal Himalaya have clearly shown the build up of aerosols in the pre-monsoon season during the winter and early spring, with relatively high values of light absorbing particulate matter including dust and black carbon (Carrico et al., 2003). Very recently, new insight into the mechanisms of aerosol trans- port from dust and pollutions sources in central and south- eastern Asia to the Tibetan and Himalayan regions was also provided by Huang et al., 2007 and Ramanathan et al., 2007. These studies indicate that aerosol in-situ and columnar con- centrations over the south slope of Himalayas are strongly affected by the development of the boundary layer, responsi- ble for transporting pollution aerosols upward, contributing to changes in solar irradiance (Dumka et al., 2006; Dumka et al., 2008; Ramachandran, 2008). Assessing the impact of aerosol particle on the local energy balance in the high alti- tude regions of Himalayas is therefore of importance for the whole area of HKH regions.

of SOA in fine particle pollution in Beijing is not well known, in particular during win- tertime, a season with frequent occurrences of pollution episodes (Sun et al., 2013b; Zhang et al., 2014). Of particular interest, this study took place in the month with the most important holiday in China, i.e., the Spring Festival. The source emissions (e.g., traffic and cooking) had significant changes due to a large reduction of population and

Le Henaff, M., Lueb, R. A., Mckeen, S. A., Meagher, J. F., Murphy, D. M., Paris, C., Par- rish, D. D., Perring, A. E., Pollack, I. B., Ravishankara, A. R., Robinson, A. L., Ryerson, T. B., Schwarz, J. P., Spackman, J. R., Srinivasan, A., and Watts, L. A.: Organic aerosol formation downwind from the Deepwater Horizon oil spill, Science, 331, 1295–1299, 2011. 30578 DeCarlo, P. F., Kimmel, J. R., Trimborn, A., Northway, M. J., Jayne, J. T., Aiken, A. C., Go-

AC concentrations of these five species are plotted analo- gously, but with RH shown to identify recent contact with the surface (Fig. 5). All of the box plots in this work show the median and the inner quartiles by the center, bottom, and top cross bars of the rectangular boxes, and the 5 % and 95 % ranges by the whiskers. To present data patterns in a continu- ous fashion, to facilitate comparisons, we also include Lo- cally Weighted Scatter Smoothing (LOWESS) (Cleveland, 1979) lines as proxies for median values. The good agree- ment between these two approaches can be seen in Figs. 5 and 6 where the LOWESS lines are overlaid on the box plots. The LOWESS fits for BC concentrations of SO 2− 4 , NH + 4 , Org, and NO − 3 (Fig. 4) exhibit pronounced longitudinal gra- dients with concentrations lower offshore than near the coast. In contrast, the median of SSA represented by Na + , exhibits a rather uniform longitudinal distribution, increasing slightly offshore. These gradients are consistent with a continental source for SO 2− 4 , NH + 4 , Org, and NO − 3 . The median AC con- centrations of SO 2− 4 and NH + 4 (Fig. 5) also exhibited a land- to-sea gradient, showing the influence of nearby terrestrial sources, likely in Chile and Peru (Allen et al., 2011). Higher AC concentrations of SO 2− 4 , NH + 4 , as well as Org, near the coast (east of ∼ 73 ◦ W) were associated with moist air (RH

Figure 7a illustrates the averaged GF-PDFs in the newly forming ML. A first compar- ison between the two dry sizes probed by the WHOPS reveals a strong resemblance of the GF-PDF shapes for GF > 1.5, except for a small shift towards larger GFs for the smaller particle size. This suggests that hygroscopic particles of these two sizes have a similar chemical composition. When, however, comparing to the HTDMA SPC obvious