Atmospheric submicron particulate matter (PM₁) is one of the most significant pollution components in China. Despite its current popularity in the studies of aerosol chemistry, the characteristics, sources and evolution of atmospheric PM₁ species are still poorly understood in China, particularly for the two harvest seasons, namely, the summer wheat harvest and autumn rice harvest. An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was deployed for online monitoring of PM₁ components during summer and autumn harvest seasons in urban Nanjing, in the Yangtze River delta (YRD) region of China. PM₁ components were shown to be dominated by organic aerosol (OA, 39 and 41%) and nitrate (23 and 20%) during the harvest seasons (the summer and autumn harvest). Positive matrix factorization (PMF) analysis of the ACSM OA mass spectra resolved four OA factors: hydrocarbon-like mixed with cooking-related OA (HOA + COA), fresh biomass-burning OA (BBOA), oxidized biomass-burning-influenced OA (OOA-BB), and highly oxidized OA (OOA); in particular the oxidized BBOA contributes ~80% of the total BBOA loadings. Both fresh and oxidized BBOA exhibited apparent diurnal cycles with peak concentration at night, when the high ambient relative humidity and low temperature facilitated the partitioning of semi-volatile organic species into the particle phase. The fresh BBOA concentrations for the harvests are estimated as BBOA = 15.1 × (m/z 60–0.26% × OA), where m/z (mass-to-charge ratio) 60 is a marker for levoglucosan-like species. The (BBOA + OOA-BB)/ΔCO, (ΔCO is the CO minus background CO), decreases as a function of f₄₄ (fraction of m/z 44 in OA signal), which might indicate that BBOA was oxidized to less volatile OOA, e.g., more aged and low volatility OOA (LV-OOA) during the aging process. Analysis of air mass back trajectories indicates that the high BB pollutant concentrations are linked to the air masses from the western (summer harvest) and southern (autumn harvest) areas.

: By analyzing the data of urban air pollutant measurements from 2013 to 2015 in Nanjing, East China, we found that the correlation coefficients between major atmospheric compound pollutants PM_2.5 and O₃ were respectively 0.40 in hot season (June, July and August) and −0.16 in cold season (December, January and February) with both passing the confidence level of 99%. This provides evidence for the inverse relations of ambient PM_2.5 and O₃ between cold and hot seasons in an urban area of East China. To understand the interaction of PM_2.5 and O₃ in air compound pollution, the underlying mechanisms on the inversion relations between cold and hot seasons were investigated from the seasonal variations in atmospheric oxidation and radiative forcing of PM_2.5 based on three-year environmental and meteorological data. The analyses showed that the augmentation of atmospheric oxidation could strengthen the production of secondary particles with the contribution up to 26.76% to ambient PM_2.5 levels. High O₃ concentrations in a strong oxidative air condition during hot season promoted the formation of secondary particles, which could result in a positive correlation between PM_2.5 and O₃ in hot season. In cold season with weak atmospheric oxidation, the enhanced PM_2.5 levels suppressed surface solar radiation, which could weaken O₃ production for decreasing ambient O₃ level with the low diurnal peaks. Under the high PM_2.5 level exceeding 115 μg·m⁻³, the surface O₃ concentration dropped to 12.7 μg·m⁻³ at noon with a significant inhibitory effect, leading to a negative correlation between PM_2.5 and O₃ in cold season. This observational study revealed the interaction of PM_2.5 and O₃ in air compound pollution for understanding the seasonal change of atmospheric environment.

A PM_2.5-capable aerosol chemical speciation monitor (Q-ACSM) was deployed in urban Nanjing, China, for the first time to measure in situ non-refractory fine particle (NR-PM_2.5) composition from 20 October to 19 November 2015, along with parallel measurements of submicron aerosol (PM₁) species by a standard Q-ACSM. Our results show that the NR-PM_2.5 species (organics, sulfate, nitrate, and ammonium) measured by the PM_2.5-Q-ACSM are highly correlated (r² > 0.9) with those measured by a Sunset Lab OC / EC analyzer and a Monitor for AeRosols and GAses (MARGA). The comparisons between the two Q-ACSMs illustrated similar temporal variations in all NR species between PM₁ and PM_2.5, yet substantial mass fractions of aerosol species were observed in the size range of 1–2.5 µm. On average, NR-PM_1−2.5 contributed 53 % of the total NR-PM_2.5, with sulfate and secondary organic aerosols (SOAs) being the two largest contributors (26 and 27 %, respectively). Positive matrix factorization of organic aerosol showed similar temporal variations in both primary and secondary OAs between PM₁ and PM_2.5, although the mass spectra were slightly different due to more thermal decomposition on the capture vaporizer of the PM_2.5-Q-ACSM. We observed an enhancement of SOA under high relative humidity conditions, which is associated with simultaneous increases in aerosol pH, gas-phase species (NO₂, SO₂, and NH₃) concentrations and aerosol water content driven by secondary inorganic aerosols. These results likely indicate an enhanced reactive uptake of SOA precursors upon aqueous particles. Therefore, reducing anthropogenic NO_x, SO₂, and NH₃ emissions might not only reduce secondary inorganic aerosols but also the SOA burden during haze episodes in China.

To evaluate the effectiveness of measures to reduce the levels of volatile organic compounds (VOCs), which are important precursors of ground-level ozone formation, the real-time monitoring data of VOCs at the urban Zhaohui supersite (ZH), the Dianshan Lake regional supersite (DSL) and the urban Yixing station (YX) in the Yangtze River Delta region were analyzed from 23 August to 15 September 2016 during the G20 Hangzhou Summit. The average mole ratios of VOCs at the three sites were 6.56, 21.33 and 19.62 ppb, respectively, which were lower than those (13.65, 27.72 and 21.38 ppb) after deregulation. The characteristics of the VOCs varied during the different control periods. Synoptic conditions and airmass transport played an important role in the transport and accumulation of VOCs and other pollutants, which affected the control effects. Using the positive matrix factorization (PMF) method in source apportionment, five factors were identified, namely, vehicle exhaust (19.66–31.47%), plants (5.59–17.07%), industrial emissions (13.14–33.82%), fuel vaporization (12.83–26.34%) and solvent usage (17.84–28.95%) for the ZH and YX sites. Factor 4 was identified as fuel vaporization + incomplete combustion (21.69–25.35%) at the DSL site. The Non-parametric Wind Regression (NWR) method showed that regional transport was the main factor influencing the VOC distribution.

Atmospheric submicron particulate matter (PM₁) is one of the most significant pollution components in China. Despite its current popularity in the studies of aerosol chemistry, the characteristics, sources and evolution of atmospheric PM₁ species are still poorly understood in China, particularly for the two harvest seasons, namely, the summer wheat harvest and autumn rice harvest. An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was deployed for online monitoring of PM₁ components during summer and autumn harvest seasons in urban Nanjing, in the Yangtze River delta (YRD) region of China. PM₁ components were shown to be dominated by organic aerosol (OA, 39 and 41%) and nitrate (23 and 20%) during the harvest seasons (the summer and autumn harvest). Positive matrix factorization (PMF) analysis of the ACSM OA mass spectra resolved four OA factors: hydrocarbon-like mixed with cooking-related OA (HOA + COA), fresh biomass-burning OA (BBOA), oxidized biomass-burning-influenced OA (OOA-BB), and highly oxidized OA (OOA); in particular the oxidized BBOA contributes ~80% of the total BBOA loadings. Both fresh and oxidized BBOA exhibited apparent diurnal cycles with peak concentration at night, when the high ambient relative humidity and low temperature facilitated the partitioning of semi-volatile organic species into the particle phase. The fresh BBOA concentrations for the harvests are estimated as BBOA = 15.1 × (m/z 60–0.26% × OA), where m/z (mass-to-charge ratio) 60 is a marker for levoglucosan-like species. The (BBOA + OOA-BB)/ΔCO, (ΔCO is the CO minus background CO), decreases as a function of f₄₄ (fraction of m/z 44 in OA signal), which might indicate that BBOA was oxidized to less volatile OOA, e.g., more aged and low volatility OOA (LV-OOA) during the aging process. Analysis of air mass back trajectories indicates that the high BB pollutant concentrations are linked to the air masses from the western (summer harvest) and southern (autumn harvest) areas.

A single particle soot photometer (SP2) was deployed in urban Nanjing, located in the Yangtze River Delta (China), to investigate the mixing state and sources of ambient refractory black carbon (rBC) from 26 January to 25 February 2014, along with an in-situ measurement of submicron aerosol chemical species by an aerodyne aerosol chemical speciation monitor (ACSM). The results showed that anthropogenic activities associated with firework emissions can be a significant source for rBC-containing particles during the period of the Chinese New Year, resulting from the evident peaks of rBC at midnight. During the residual periods, namely regular day (RD), the diurnal cycles of rBC presented two typical peaks that can be attributed to a synergistic influence of local traffic emissions and boundary layer changes throughout a day. Three coating factors, including organics, sulfate, and nitrate (-rich), were resolved using a positive matrix factorization (PMF) approach to explain the potential contribution of non-rBC coatings (i.e., organics, sulfate, and nitrate) to the coating thickness of rBC-containing particles. As the results show, organic aerosols (OAs) might be a major contributor to the coating thickness of rBC-coating particles during the whole period. The relative coating thickness (a ratio between coated particle size to BC core) exhibited a positive relationship with sulfate, indicative of the favorable coating factor during the episode caused by firework emissions. Source apportionment of rBC was performed via a multiple linear regression between the total rBC mass and each ACSM-PMF factor (rBC-ACSM-PMF). On average, biomass burning emissions accounted for 43%, being the largest contributor during the RD period, whereas local traffic emissions played a major role during the new year time.