Submicron aerosol particles (PM₁) were measured in-situ using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer during the summer 2009 Field Intensive Study at Queens College in New York, NY. Organic aerosol (OA) and sulfate are the two dominant species, accounting for 54% and 24%, respectively, of the total PM₁ mass. The average mass-based size distribution of OA presents a small mode peaking at ~150 nm (<i>D</i>_va) and an accumulation mode (~550 nm) that is internally mixed with sulfate, nitrate, and ammonium. The diurnal cycles of both sulfate and OA peak between 01:00–02:00 p.m. EST due to photochemical production. The average (±σ) oxygen-to-carbon (O/C), hydrogen-to-carbon (H/C), and nitrogen-to-carbon (N/C) ratios of OA in NYC are 0.36 (±0.09), 1.49 (±0.08), and 0.012 (±0.005), respectively, corresponding to an average organic mass-to-carbon (OM/OC) ratio of 1.62 (±0.11). Positive matrix factorization (PMF) of the high resolution mass spectra identified two primary OA (POA) sources, traffic and cooking, and three secondary OA (SOA) components including a highly oxidized, regional low-volatility oxygenated OA (LV-OOA; O/C = 0.63), a less oxidized, semi-volatile SV-OOA (O/C = 0.38) and a unique nitrogen-enriched OA (NOA; N/C = 0.053) characterized with prominent C_xH_{2x + 2}N⁺ peaks likely from amino compounds. Our results indicate that cooking and traffic are two distinct and mass-equivalent POA sources in NYC, together contributing ~30% of the total OA mass during this study. The OA composition is dominated by secondary species, especially during high PM events. SV-OOA and LV-OOA on average account for 34% and 30%, respectively, of the total OA mass. The chemical evolution of SOA in NYC appears to progress with a continuous oxidation from SV-OOA to LV-OOA, which is further supported by a gradual increase of O/C ratio and a simultaneous decrease of H/C ratio in total OOA. Detailed analysis of NOA (5.8% of OA) presents evidence that organic nitrogen species such as amines might have played an important role in the atmospheric processing of OA in NYC, likely involving both acid-base chemistry and photochemistry. In addition, analysis of air mass trajectories and satellite imagery of aerosol optical depth (AOD) indicates that the high potential source regions of secondary sulfate and aged OA are mainly located in regions to the west and southwest of the city

[1] Measurements of ambient formaldehyde (HCHO), related gases and particulate matter were carried out from the SUNY Albany mobile platform at the Queens College site in New York City (NYC) from 15 July to 3 August 2009. Ambient HCHO was measured using a quantum cascade laser (QCL) trace gas detector. HCHO concentrations ranged from 0.4 to 7.5 ppb with a mean value of 2.2 AE 1.1 ppb. Daily HCHO peaks were nearly always found between 1100 EST (Eastern Standard Time) and noontime throughout the sampling period. HCHO correlated strongly with NOx and black carbon during the traffic rush hours, but around noontime HCHO correlated much better with total oxidants (Ox = O 3 + NO 2 ). Using the diurnal pattern of HCHO/BC ratios, we estimated that 70% of HCHO present between 1200 EST to 1500 EST was produced by photochemical reactions. Sources of photochemically produced HCHO were calculated using measured concentrations of hydrocarbons, their reaction kinetics with OH radicals, and HCHO yields. These calculations indicated that isoprene oxidation was the dominant source of HCHO for this period at this site, responsible for 44%, followed by methane (25%) and propene (18%). To assess the impact of HCHO as a radical source, the HOx production rates from HCHO, HONO, O 3 photolysis, and alkenes +O 3 were calculated as well. Daily averaged HOx production rates from HONO, HCHO, O 3 photolysis and alkenes +O 3 were 8.6 Â 10 6 , 2.3 Â 10 6 , 1.7 Â 10 6 , 2.1 Â 10 5 molecules cm À3 s À1 , respectively, contributing 67, 18, 13 and 2% to the overall daily HOx radical budget from these precursors.

Abstract.We have investigated an aerosol processing and evolution event from 21-22 July during the summer 2009 Field Intensive Study at Queens College in New York City (NYC). The evolution processes are characterized by three consecutive stages: (1) aerosol wet scavenging, (2) nighttime nitrate formation, and (3) photochemical production and evolution of secondary aerosol species. Our results suggest that wet scavenging of aerosol species tends to be strongly related to their hygroscopicities and also mixing states. The scavenging leads to a significant change in bulk aerosol composition and average carbon oxidation state because of scavenging efficiencies in the following order: sulfate > low-volatility oxygenated organic aerosol (LV-OOA) > semi-volatile OOA (SV-OOA) > hydrocarbon-like OA (HOA). The second stage involves a quick formation of nitrate from heterogeneous reactions at nighttime. During the third stage, simultaneous increases of sulfate and SV-OOA were observed shortly after sunrise, indicating secondary aerosol formation. Organic aerosols become highly oxidized in ∼ half day as the result of photochemical processing, consistent with previously reported results from the CO-tracer method (OA/ CO). The photochemical reactions appear to progress gradually associated with a transformation of SV-OOA to low-volatility species based on the evolution trends Correspondence to: Q. Zhang (dkwzhang@ucdavis.edu) of oxygen-to-carbon (O/C) ratio, relationship between f44 (fraction of m/z 44 in OA) and f43 (fraction of m/z 43 in OA), and size evolution of OOA and HOA. Aerosols appear to become more internally mixed during the processing. Our results suggest that functionalization by incorporation of both C and O plays a major role in the early period of OA oxidation (O/C < 0.5). Our results also show that photochemical production of LV-OOA during this event is approximately 2-3 h behind of sulfate production, which might explain, sometimes, the lack of correlations between LV-OOA and sulfate, two secondary aerosol species which often exist in internal mixtures over regional scales.

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This study examines age-related differences in inhibitory control as measured by stop-signal performance. The participants were 24 adults aged 20-30 years and 24 older adults aged 61-76 years. The task blocks were pure choice reaction-time blocks, global stop-signal blocks (with an auditory stop signal), and selective stop-signal blocks (with valid and invalid stop signals). There was a decline in reactive inhibitory control for the older group reflected by greater stop-signal reaction times and reduced P3 peak amplitudes in both global and selective stop-signal task blocks. The decreased reactive inhibitory control might result from speed-accuracy tradeoffs. Conversely, no age-related decline in proactive inhibitory control was observed. This was reflected by slower response times (RTs) and reduced P3 peak amplitudes during GO trials in blocks with stop-signals relative to those in blocks of pure choice reaction-time tasks, and in which the RT and amplitude differences were similar between groups. The results further show age-related compensation responses associated with proactive inhibition, such as increased activation at the frontal site among older participants, resulting in no differences in P3 peak amplitudes between electrode sites, and smaller differences at the Fz site than other sites compared with younger adults. For older adults, the P3 peak amplitude at the Fz site was significantly correlated with the RT of proactive inhibitory control. This shows that larger RT differences were associated with larger reductions in P3 peak amplitudes in the stop-signal blocks relative to the pure choice blocks. These results appear to support age-related compensation hypotheses.